Sun light vs. damage & Vit.D

[Kasper]

Indirect sunlight can also damage the skin.
Don't get too much UVB exposure, if it's direct or indirect, doesn't matter.
Too much UVB exposure (in the sense that you've signs of burning) won't help you width vitamin D.
I think everybody agrees here that you should not get burned.
Although... panacea wrote an interesting post about raw food/sunburn connection.

For the vitamin d, if you can't get it because you live too far from the equator and don't have the time, or are dark skinned and live far from equator which makes it even worse, your best bet is to stay 100% wai and then get a narrowband UVB lamp which will blast you for about 5 minutes per day while you wear protective eye goggles. If you don't stay 100% wai and you are prone to tanning then you can get sunburn and negative health affects from these lamps. Even eating a single potato chip can cause you to get a sunburn from these (or going to the beach). As long as you eat perfectly for atleast a month though, you can test it and go to the beach and try to get a sunburn and it won't happen. I'm sure RRM can confirm this and tell us he hasn't had a sunburn since being Wai unless he cheated.

Is this correct RRM?
Overkees also told me he didn't get sunburn when 100% Wai.

[overkees]

I think it has a lot to do with omega 3 vs omega 6 and the amount of antioxidants we ingest to counteract a sunburn. Also standing barefoot on the ground should have an impact. Also doing buteyko will help alot I guess. I think it's because the oxidative stress, and the prevention of it in other parts of the body. But I must add that I don't overdo sitting in the sun, like some people with sunscreen tend to do. I spend 3/4 to 1 hour max in the sun (30+ degrees) and I get in the shade for at least 15 minutes after that, because my body tells me to. I rarely go out in the sun for sunbathing alone. I did not use sunscreen or aftersun.

My mother has the same colour as me, she was exposed to the same sun, in the same vacation, only a lot less time than me, and she burned herself pretty bad. She did use aftersun. I was doing wai for 2.5 weeks 100% back then plus buteyko and walking alot barefoot.

But sunburning is totally not the issue here in my opinion. White people already get good amounts of vitamin D if only exposed for a short time, so sunburning will not be the case here.

looked for some research regarding sunburning and a good diet:

http://www.ncbi.nlm.nih.gov/pubmed/20854436
http://www.ncbi.nlm.nih.gov/pubmed/20219323
http://www.ncbi.nlm.nih.gov/pubmed/21733837
http://www.ncbi.nlm.nih.gov/pubmed/21217086
http://www.ncbi.nlm.nih.gov/pubmed/12807737

[RRM]

- Serum PTH×25(OH) D levels in 393 healthy adolescent females (12–18 years).
The data suggested that the change in the slope of the plot for serum 25(OH)D from negative to positive occurred at 90 nmol/l.
- Guillemant and colleagues found that when 25(OH) levels fell below 83 nmol/l when assayed using the CPB method, the increase in PTH concentration accelerated
- Chapuy and colleagues [14] reported that in French adults (35–60 years), serum PTH levels were stable at a 25(OH)D concentration of 78 nmol/l (CPB assay)

Ah, this is more like it!
I will look into these studies when i have some time.

Hmm. Found some more info on this issue, and lower levels.

Dose response to vitamin D supplementation in postmenopausal women: a randomized trial.
"[The] RDA [is] defined as meeting the needs of 97.5% of the population for vitamin D(3)".
"A vitamin D(3) dosage of 800 IU/d increased serum 25-(OH)D levels to greater than 50 nmol/L (> 20 ng/ml) in 97.5% of women;
however, a model predicted the same response with a vitamin D(3) dosage of 600 IU/d."
"The dose response was curvilinear and tended to plateau at approximately 112 nmol/L in patients receiving more than 3200 IU/d of vitamin D(3)."

So, here the maximum was about 112 nmol / L.

Vitamin D status in healthy Indians aged 50 years and above.
"PTH levels started rising at vitamin D level < 30 ng/ml (75 nmol/L).
However, more than 50% of subjects with severe Vitamin D deficiency (< 20 ng/ml or < 50 nmol/L) had PTH levels within normal range.

So, from these studies we may conclude that what officially constitutes as a severe vitamin D deficiency, may for some in practise not be a deficiency at all,
which makes sense, because the RDA has to meet the requirements for 97.5% of the population.
Whats also interesting:
"Normal bone mass was observed in only 18.6% of study subjects" (first study above)
Whereas their osteoporotic fractures rates are lower than in the Netherlands.
Moreover, what oficially constitutes a vitamin D deficiency, may not be so at all.
Very often there are no deficiency symptoms or adverse health effects at all,
and even PTH levels may get adjusted despite (too) low vitamin D levels:

Factors associated with elevated or blunted PTH response in vitamin D insufficient adults.
"Our results indicate that during vitamin D insufficiency, factors other than calcium and vitamin D may modify PTH response".

In rickets patients, PTH is extremely high:
"Mean (SD) PTH level was 23.59 (19.03) pmol/L in the rachitic group and 1.9 (1.05) pmol/L in controls" Al-Mustafa ZH et al
and yet, 10% of them dont lack sunexposure.
25% of them had vitamin D levels greater than 20 nmol/L.

And even in secondary HPTH its not a clear case.
Causes of secondary hyperparathyroidism in a healthy population: the Tromsø study.
"serum 25-hydroxyvitamin D levels were significantly lower in the secondary hyperparathyroid (SHPT) group but only in nonsmokers..."
"in most subjects with SHPT all tests were within the normal range, and the cause is therefore probably a combination of several factors".

Logically, how much vitamin D is needed, is also debatable:
Regulation of PTH secretion by 25-hydroxyvitamin D and ionized calcium depends on vitamin D status: a study in a large cohort of healthy subjects.
"Our results indicated that PTH levels were highly conditioned by those of 25OHD in subjects with 25OHD values lower than 16.35 ng/mL"[/i] (40.9 nmol/L)

High prevalence of vitamin D deficiency in the sunny Eastern region of Saudi Arabia: a hospital-based study.
"Serum 25(OH)D levels ...were low [10.1 (SD 4.6) ng/mL and 9.9 (SD 4.5) ng/mL respectively] (25 nmol/L). When subjects with elevated PTH levels were excluded, serum 25(OH)3 levels were still in the deficiency range."

Serum parathyroid hormone in healthy Japanese women in relation to serum 25-hydroxyvitamin D.
"Intact PTH increased with age" ... "there is no association between serum 25(OH)D and PTH levels in this Japanese population,
supporting a cutoff level of 25(OH)D less than 37.5 nmol/L for the elevated PTH level."

The 25(OH)D/PTH threshold in black women.
"Black women have lower 25-hydroxyvitamin D [25(OH)D] and higher PTH than white women".
"Black women (14.8 ng/ml = 37 nmol/L) have an increase in serum PTH at a lower 25(OH)D level than white women (23,6 ng/ml = 59 nmol/L)."

Optimal vitamin D status and serum parathyroid hormone concentrations in African American women.
"breakpoint between (16 and 20 ng/ml) 40 nmol/L and 50 nmol/L for serum 25(OH)D."

Prevalence of vitamin D deficiency among adult population of Isfahan City, Iran.
[ii]"the cut-off point of serum 25-OHD was determined to be 30 ng/mL" (75 nmol/L)"[/i]

Reference range for serum parathyroid hormone
"Serum PTH was significantly higher in black study subjects than in white study subjects"

Vitamin D status in a sunny country: where has the sun gone?
"After the winter, median s25(OH)D was 21.4 ng/mL and 77.4% of the population presented hypovitaminosis D. ...
Significant increase in s25(OH)D was verified after summer [10.6 (3.7-19.3 ng/ml); p<0.001]...
We also observed a significant decrease in hyperparathyroidism prevalence (20.8% vs. 4.9%; P<0.0001)."

Effect of different dress style on vitamin D level in healthy young Orthodox and ultra-Orthodox students in Israel.
"PTH was normal in 87% of vitamin D-deficient subjects from Yeshiva-A and Yeshiva-C (mean age 20), compared to 52% of Yeshiva-B students (mean age 33)."

Assessment of vitamin D status in healthy children and adolescents living in Tehran and its relation to iPTH, gender, weight and height.
"Severe [vitamin D] deficiency was detected in 25% of subjects, deficiency in 27% and insufficiency in 26%...
The subjects did not have any signs or symptoms of rickets....
The curve of iPTH began to rise when 25(OH)D reached 75 nmol/L"

Predictors of vitamin D status and its association with parathyroid hormone in young New Zealand children
"When 25(OH)D concentrations were >60-65 nmol/L, a plateau in PTH was evident."

Prophylactic vitamin D in healthy infants: assessing the need.
"breast-fed infants aged 3 months had the lowest value (20.2 ng/mL)" (50.5 nmol/L)
"The clinical relevance of these findings is probably negligible because serum 25OHD levels spontaneously increased with age and were not associated with high serum PTH."

Even consuming only 2.25 ug/day, being indoors most of the day, some individuals will still not have inadequate blood vitamin D. (not that we recommend it!)
Prevalence of hypovitaminosis D and folate deficiency in healthy young female Austrian students in a health care profession.
"Mean daily ingestion of vitamin D was 2.25 μg/day .... 6.9% had hypovitaminosis D (25-OH-vitamin D(3) <30 nmol/L) and 89.3% were vitamin D insufficient (<75 nmol/L)."

This one is 'funny':
Impact of two regimens of vitamin D supplementation on calcium - vitamin D - PTH axis of schoolgirls of Delhi.
"Despite supplementation with 60,000 IU of Vitamin D₃(monthly or two-monthly), only 47% were vitamin D sufficient at the end of one year."

Both skin types show that there is a mechanism which makes sure vitamin D production in the skin is stopped at a certain level.

"Stopped"? At what level?
You really mean as in: "no further increase whatsoever"?
Any evidence to back this up?
(or do you mean "plateau on average at...")

To estimate the circulating 25(OH)D concentrations prevalent in humans of the late Paleolithic period, we need to focus on people in sun-rich environments who regularly expose most of their skin surface to the sun.

Nonsense. In Europe, vast areas of land were covered by thick forests.

The Paleolithic period ends around 10,000 BP.
The last glacial period was the most recent glacial period within the current ice age occurring from approximately 110,000 to 10,000 BP.
Ecological zones in Europe at the last glacial maximum, ca 18,000 BP, are estimated to look like this:...
...Only at some coastal regions, we see a lot of forest.

In the last Paleolithic period, the ice was retreating.
The forests came back.
From 18,000 BP to 10,000 BP a lot of forest may have grown.
But if you still insist that there was little forest in Europe around 10,000 BP anyway,
then lets look a little further in the history of evolution of mankind in Europe (as we are both white europeans).
What we see then (until very recently), is a lot of forest, covering vast areas of land.
Hence much less UVB exposure.
So, again, to even estimate UVB exposure in the evolution of white europeans, is pure speculation,
and very much depends on what period of time in history is the subject of our speculations.

Most forest in europe originated after the last glacial period. First signs of agriculture are around the same period.
It's more likely that our DNA adopted to agriculture, than it adopted to living predominantly in thick forests width limited UVB exposure.

Huh?
Are you really claiming that since 10,000 BP there were no hunter gatherers in Europe anymore?
Only farmers?

On most days, the sun may have been blocked by clouds, dont you think?

According to you: "Cloud cover reduces UV levels, but not completely; you [can] get burned on a cloudy day."

So, much less UVB exposure.

I don't think that on MOST days the sun was blocked, but I don't know the climate back than.

Wise words, acknowledging another point of speculation in this issue.

Of course, its speculation. In some sense, that's what all science is.
It's about making the best guess (model)

In this case, there is too much speculation, which makes it very unconvincing.
I dont think that guessing is good enough.
So, we better stick to the more scientific way to determine the required level of a vitamin.
(by establishing the levels of deficiency / insufficiency / sufficieny via the presence/absence of deficiency symptoms)
"Serum 25-hydroxyvitamin D (25-[OH]D) is considered the best biomarker of clinical vitamin D status". Gallagher JC et al

Indirect sunlight can also damage the skin.

Of course, if you expose yourself too long, but with direct sun exposure, it happens much faster.
So, if you want to minimize UVB induced damage, i advice to avoid direct sun exposure.

[overkees]

The antioxidants are of course linked immediately to the prevention of sunburn, as you can see in a couple of the articles I linked to. But I added the latter part of the sentence for the omega 3s vs omega 6. Omega 6 is inflammatory and omega 3 anti inflammatory. And they need the same enzymes, therefore ingesting a lot less omega 6 oils and eating more fish in general will result in a better ratio and therefore less inflammation of for example our GI. Therefore, anti oxidants are less needed in that place and can counteract the sunburning effect much better. That was my point.

But in the article below there is some very good evidence that it can also lead to a more direct protection against skin cancer and aging of the skin.

http://cebp.aacrjournals.org/content/20/3/530.long

There are a lot of anecdotal reports that people on raw diets rarely burn in the sun, even when overexposed. This does not mean that it's healthy to stay in the sun too long, but that its effects are less damaging than on a normal diet, due to several factors.

That omega 6 fatty acids are pretty bad for sun damage is also very evident: http://www.ncbi.nlm.nih.gov/pubmed/1502 ... t=Abstract

Too bad there is only little research on this subject on humans..

[Kasper]

Are you really claiming that since 10,000 BP there were no hunter gatherers in Europe anymore?
Only farmers?

No, I didn't say that. Please read my words more carefully.

In this case, there is too much speculation, which makes it very unconvincing.
I dont think that guessing is good enough.
So, we better stick to the more scientific way to determine the required level of a vitamin.

You might find it very unconvincing, many think it's quite convincing.
Every other way of determining the optimal level of vitamin D is as much a guess as this one.
If you are convinced that another way of determining the optimal level of vitamin D is a much better guess than what I did, than I'm interested of course.

I won't be able to spend much time on the wai forums the next few weeks, as I need to focus for 1000% on my study.
But I'll be back after that :)

[RRM]

Therefore, anti oxidants are less needed in that place and can counteract the sunburning effect much better. That was my point.

Yes, one of the effects of UVA and UVB is the formation of free radicals and reactive oxygen species,
and antioxidants counteract this.
UVB however, also causes direct damage to DNA (not via free radicals and ractive oxygen species),
which cannot be counteracted/prevented by antioxidants.

[RRM]

It's more likely that our DNA adopted to agriculture, than it adopted to living predominantly in thick forests width limited UVB exposure.

Are you really claiming that since 10,000 BP there were no hunter gatherers in Europe anymore?
Only farmers?

No, I didn't say that. Please read my words more carefully.

I know you didnt say that. Im just trying to figure out what your reasoning is here.
So, if there were hunter gatherers living in these thick european forests with limited UVB exposure, for thousands of years,
couldnt it be that their DNA adapted to that?

If you are convinced that another way of determining the optimal level of vitamin D is a much better guess than what I did, than I'm interested of course.

I already told you; by establishing at what levels all vitamin D deficiency symptoms are absent.

BTW, you didnt answer this one:

Both skin types show that there is a mechanism which makes sure vitamin D production in the skin is stopped at a certain level.

"Stopped"? At what level?
You really mean as in: "no further increase whatsoever"?
Any evidence to back this up?
(or do you mean "plateau on average at...")

I hope you can answer it next time, as its quite essential.

[Kasper]

So, if there were hunter gatherers living in these thick european forests with limited UVB exposure, for thousands of years,
couldnt it be that their DNA adapted to that?

Well IF these hunter gatherers were living predominantly in these thick European forest, for thousand of years, it could be that their DNA adapted to that. I agree.
It could be that their skin became more white. It could be that their DNA adapted so that they enjoyed direct sunlight much more than before.
BUT that ALL the necessary genes completely adapted to a way lower hormone (vitamin D) level... that seems absolutely impossible to me.

I already told you; by establishing at what levels all vitamin D deficiency symptoms are absent.

If you look at deficiency symptoms, you may find a good level to prevent those deficiencies.
But I really doubt if only looking at deficiency symptoms are enough to find the optimal level of vitamin D.
It's much more complex than most vitamins, as it is hormone which many different functions.
Therefore I would say, that as long as the details of the biochemical functions of vitamin D in our body aren't revealed.
Estimating our natural vitamin D level, would give us a much better guess than when we only consider deficiency symptoms.

I hope you can answer it next time, as its quite essential.

In four weeks, sorry, I need to really stop this discussion now.. I'm spending way to much time on this ..

[RRM]

the fact that we needed to get out in the sun everyday during that period.

Many native peoples live(d) in thick forests.
Our evolution confines long periods of time when the lands were substantially covered by forests.
Only during relatively short periods of time, some of that land was covered by ice.

The plateau where vitamin D synthesis in the skin is in an equillibrium for me

What level is that?

[overkees]

I have found some interesting articles, this one is about people of hawaii who spend alot of time outdoors http://jcem.endojournals.org/content/92/6/2130.long that have a vitamin D status that still is pretty low.

Also this article http://www.circumpolarhealthjournal.net ... ml#CIT0030 the northern people who almost get no vitamin D in the diet and also not from the sun. They had 15000 years to adapt.
They also state that darker skinned people can cope better with low vitamin D levels than white people. Because they can prevent the bone loss via other mechanisms of increasing the calcium absorption and phosphorus absorption rates.

Also this research is really interesting: http://cancerpreventionresearch.aacrjou ... ts/PL04-05

I think the optimum can be established but it depends heavily on your ancestors and skin colour. I still think that, with the added researches, for white people the optimum will be higher than what the RDA recommends. I still stay with my previous assumption that eating fatty fish regularly and not overdoing it in the sunlight, but not neccesarily avoiding it either with result in a healthy vitamin D balance that is very natural. This seems the most reasonable conclusion.

[RRM]

So, if there were hunter gatherers living in these thick european forests with limited UVB exposure, for thousands of years,
couldnt it be that their DNA adapted to that?

... that ALL the necessary genes completely adapted to a way lower hormone (vitamin D) level... that seems absolutely impossible to me.

Maybe they did not have to adapt to a way lower hormone level at all.
It might be that they just had to adapt to the much lower UVB exposure, in such a way that they could still get sufficient vitamin D from that,
and/or that they increased the sensitivity of the receptors.
That is what usually happens:
If the availability of a certain vitamin / mineral is low, our body tries to increase the absorption rate (or receptor sensitivity in case of hormones) accordingly.
So, if UVB exposure decreases, our body tries to compensate for that by utilizing dietary vitamin D more efficiently,
and / or by increasing the efficiency of UVB induced vitamin D production.

But I really doubt if only looking at deficiency symptoms are enough to find the optimal level of vitamin D.

I agree.
But we can find out.
What is the average vitamin D level in healthy people that get various levels of sun exposure?

What is that equilibrium?

The amount of vitamin D we synthesize when exposed to the sun.

What is that amount?
Some claim its about 250 µg (10,000 IU) per day (from 20 minutes up to 2 hours of sun exposure)
Its also claimed that the relationship between circulating vitamin D and 25(OH)D may define how much vitamin D we need,
based on the idea that 25{OH}D plateaus (at about 135 nmol/L) relative to circulating D3 levels.

A serum level of 25-hydroxyvitamin D lower than 15 nanograms per milliliter (ng/mL)—equivalent to 37.5 nanomoles per liter (nmol/L)—is generally considered inadequate.

Also this article http://www.circumpolarhealthjournal.net ... ml#CIT0030 the northern people who almost get no vitamin D in the diet and also not from the sun. They had 15000 years to adapt.

Yes, it has been shown many times that healthy Inuit (low PTH) and Amerindians may have very low vit.D levels.
30% having a 25(OH)D level lower than 37.5 nmol/L Weiler AH et al
The idea is that their 25(OH)D receptors may be more sensitive, and that more 25(OH)D is converted into 1,25(OH)2D. Rejnmark L et al
They conclude that:
"Clearly, humans have successfully adapted to environments where vitamin D is much less available through solar UVB synthesis in the skin or through dietary intake. Such adaptation has probably come about through a number of physiological changes, given the complexity of vitamin D metabolism and the possibilities for alternate metabolic pathways.
... Our vitamin D norms may simply reflect what is normal for humans whose physiology has adapted to lighter skin, lower latitudes and more solar UVB.
... if lower serum 25(OH)D levels simply reflect a lower optimal range, dietary supplementation might push treated individuals into a zone of suboptimal or even adverse outcomes."

you fail to make the point when there is an excess of vitamin D.

Too much vitamin D may result in too high blood calcium levels, which may cause calcium precipitation in the arteries and calcification of various organs.

[RRM]

Modern humans who live in sunny countries and spend much time in the sun have at least 100-140nmol/L, and more likely 135-225nmol/L in the summer.

Data from some sunny countries:

Tanzania
Traditionally living populations in East Africa have a mean serum 25-hydroxyvitamin D concentration of 115 nmol/l.
"The mean serum 25(OH)D concentrations of Maasai and Hadzabe were 119 (range 58-167) and 109 (range 71-171) nmol/l, respectively."
Serum 25-hydroxy-vitamin D3 concentrations increase during tuberculosis treatment in Tanzania.
"Median serum 25[OH]D concentrations increased from 91 nmol/l at baseline to 101 nmol/l after 2 months of TB treatment ...
Improved dietary intake and increased sunlight exposure may have contributed to the increased 25[OH]D concentrations."

Ethiopia
Low levels of serum calcidiol in an African population compared to a North European population.
"median values ...young Ethiopians 23.5 nmol/L ... pregnant Ethiopians 25 nmol/L"

Nigeria
Vitamin D status of seminomadic Fulani men and women.
"83% of the women and 45% of the men had serum 25-hydroxyvitamin D levels in the hypovitaminosis D range; 10-30 ng/mL (25-75 nmol/L)."

Gambia
Vitamin D status does not influence the breast-milk calcium concentration of lactating mothers accustomed to a low calcium intake.
"plasma 25-hydroxy-vitamin D concentration of the Gambian women (60 Gambian mothers ) ...64.4 nmol/L"

Hawaii (found by overkees)
N. Binkley et al 93 healthy adults (37 white, 27 asian, 18 mix, 7 hawaiian), Honolulu. Average sunexposure: 4.1 hours / day.
results:
average 25(OH)D: 31.6 ng/ml. (79 nmol/L).
highest 25(OH)D: 62 ng/ml. (155 nmol/L)
51% of this population had low vitamin D status (below 30 ng/ml = 75 nmol/L).

California
Plasma 25-hydroxyvitamin D and its determinants in an elderly population sample.
"290 men and 469 women aged 67-95 y... Mean 25(OH)D concentrations were 82 nmol/L in men and 71 nmol/L in women...
None of the known or suspected determinants of vitamin D status could explain the lower 25(OH)D concentrations in women"

Florida
Vitamin D status and Framingham risk score in overweight postmenopausal women.
"Mean serum 25(OH)D concentration was 65.3 nmol/L (range 7.0-147.6 nmol/L); 66% (<75 nmol/L) and 32% (<50 nmol/L) of subjects were vitamin D insufficient."

Brazil
Vitamin D status in a sunny country: where has the sun gone?
"After the winter...77.4% of the population presented hypovitaminosis D...
After the summer, median s25(OH)D was 32 ng/mL (80 nmol/L)"
Prevalence of vitamin D insufficiency in Brazilian adolescents.
"mean 25(OH)D concentration was 73.0 nmol/l (29.2 ng/ml]. Vitamin D insufficiency was observed in 60% of adolescents"

Argentina
Vitamin D deficiency and osteoporosis in a rural population of Cordoba province, Argentina
"Córdoba High mountains... over 50 years old... Mean blood Vitamin D level was 24.54 ng /ml (61.35 nmol/L)"

Guatamala
Older Mayan residents of the western highlands of Guatemala lack sufficient levels of vitamin D.
"residences in areas receiving ample sunlight at high altitudes and latitudes near the equato... 108 healthy older Mayans (mean age, 69 years)
Mean serum 25(OH)D values were 53.3 nmol/L... 50% (n = 54) had values between 50 and 80 nmol/L, and 46.3% (n = 50) had levels less than 50 nmol/L."[/i]

Mexico
Serum vitamin D and breast density in breast cancer survivors.
"426 postmenopausal breast cancer survivors ... 24% vitamin D deficiency (serum [25(OH)D], < 40 nmol/L ...
those with sufficient status (23%; serum [25(OH)D], > or = 80 nmol/L .... 53% > 40 nmol/L but < 80 nmol/L ...[/i]"

Puerto Rico
Determinants of vitamin D status among overweight and obese Puerto Rican adults.
"31% had levels between 20 and 30 ng/ml (50 and 75 nmol/L) and 14% had levels <20 ng/ml (<50 nmol/L".

Australia
Does a high UV environment ensure adequate vitamin D status?
"10.2% of the participants had serum 25(OH)D levels below 25 nmol/l (considered deficient) and a further 32.3% had levels between 25 nmol/l and 50 nmol/l (considered insufficient)"
Vitamin D status of adults from tropical Australia determined using two different laboratory assays: implications for public health messages.
"...ambulatory adults ... Mean levels were 68.3 (range 26-142) by DiaSorin Radioimmunoassay and 83.0 (range 30-184) by DiaSorin Liaison® one."
"6.2% had 25(OH)D levels between 25 and 50 nmol/L "

New Zealand
Vitamin D insufficiency and health outcomes over 5 y in older women
"mean age of 74 y... 50% of women had a seasonally adjusted 25(OH)D concentration <50 nmol/L. ...
not at risk of adverse outcomes over 5 y after control for comorbidities"
The effects of seasonal variation of 25-hydroxyvitamin D and fat mass on a diagnosis of vitamin D sufficiency.
"postmenopausal... 73% of women and 39% of men were predicted to have trough 25(OH)D concentrations < 50 nmol/L, according to the demonstrated seasonal variation".

Korea
High prevalence of vitamin D insufficiency or deficiency in young adolescents in Korea.
"vitamin D insufficiency (<50 nmol/L)) or deficiency (52-72 nmol/L) was found in 98.9 % of boys and 100 % of girls"

South Asia
Vitamin D deficiency in UK South Asian Women of childbearing age
"Serum 25(OH)D <25 nmol/L was highly prevalent in South Asians in the winter (81 %) and autumn (79.2 %)."

Japan
Low serum concentrations of 25-hydroxyvitamin D in young adult Japanese women: a cross sectional study.
"mean serum 25(OH)D concentration in women younger than 30 y was 34.0 nmol/L ... less than 30 nmol/L was 42.1%
...in women 30 y and older 50.0 nmol/L. ... less than than 30 nmol/L was 10.3%"
Summer/winter differences in the serum 25-hydroxyvitamin D3 and parathyroid hormone levels of Japanese women.
"subjects with higher summer 25(OH)D3 values having greater reductions in winter 25(OH)D3 concentrations."

Malaysia
Vitamin D status and its associated factors of free living Malay adults in a tropical country, Malaysia.
"Their mean age was 48.5±5.2years and the mean 25(OH)D for males and females were 56.2 nmol/L and 36.2 nmol/L respectively."

India
Presence of 25(OH) D deficiency in a rural North Indian village despite abundant sunshine.
"even with five hours of daily sunshine exposure only 31.5% had serum 25(OH)D levels > or = 50 nmol/L"
Vitamin D Status in India – Its Implications and Remedial Measures
"All Indian studies uniformly point to low 25(OH)D levels in the populations studies despite abundant sunshine."
Vitamin D status in healthy Indians aged 50 years and above.
"more than 50% of subjects with severe Vitamin D deficiency; < 20 ng/ml (< 50 nmol/L)"
High prevalence of hypovitaminosis D in young healthy adults from the western part of India.
"70% of the study population had hypovitaminosis D; <20 ng/ml (< 50 nmol/L)

Spain
Vitamin D deficiency in South Europe: effect of smoking and aging.
"Mean levels of 25(OH)D were 24.0 ng/ml (60 nmol/L).
76% was <30 ng/ml (75 nmol/L), including 4.5% < 10 ng/ml (25 nmol/L)."
Influence of sun exposure and diet to the nutritional status of vitamin D in adolescent Spanish women
"Serum levels of 25(OH)D were higher during the summertime (61.55 nmol/L) than in winter (45.81 nmol/L)
During the summer, vitamin D insufficiency (< 50 nmol/L) affected 17% of the population, going up to 63% in the winter."

couldnt it be that their DNA adapted to that?

... that ALL the necessary genes completely adapted to a way lower hormone (vitamin D) level... that seems absolutely impossible to me.

Maybe they did not have to adapt to a way lower hormone level at all.

It seems that humans are highly adaptive, regarding UVB exposure and 25(OH)D levels...
Exposed to less sunlight, with every generation their capacity to convert sunlight/dietary D into circulating D, became more potent.

Blood vitamin D levels in relation to genetic estimation of African ancestry. (in the USA)
"The mean serum 25(OH)D levels among Whites (68 nmol/L) and among African-Americans of low (48.8 nmol/L), medium (45.8 nmol/L), and high (41.3 nmol/L) African ancestry were 27.2, 19.5, 18.3, and 16.5 ng/mL, respectively. Serum 25(OH)D was estimated to decrease by 1.0 to 1.1 ng/mL per 10% increase in African ancestry. The effect of high vitamin D exposure from sunlight and diet was 46% lower among African-Americans with high African ancestry than among those with low/medium ancestry."

So, when exposed to less sunlight, in just a few hundreds years, humans can adapt to the extend of 7 nmol / L.
Potentially, thats about 170 nmol / L of adaptation in 10.000 years...
Why is it then that the difference between white and black people (living in the same country) is so much smaller? (only 27 nmol / L)
Obviously because there is no ultimate benefit in going higher than that. (68 nmol/L in this case)

What is our optimal level of vitamin D?

Evolutionary, it may have been much lower than you think.
Sure, higher levels may be optimal for certain conditions (eg breast cancer, lung cancer) compared to very low levels,
but elevated vitamin D levels are equally harmful:

Overview of the Cohort Consortium Vitamin D Pooling Project of Rarer Cancers.
"Across each cancer site, there was no evidence of a protective association between higher concentrations of 25-hydroxyvitamin D (>75 nmol/L) and cancer outcome. ... An increased risk at very high levels (> or =100 nmol/L) was noted for pancreatic cancer"

Vitamin D and osteogenic differentiation in the artery wall
"there is a narrow range of vitamin D levels in which vascular function is optimized".

Vitamin D and aging
"a high vitamin D activity showed features of premature aging that include retarded growth, osteoporosis, atherosclerosis, ectopic calcification, immunological deficiency, skin and general organ atrophy, hypogonadism and short lifespan."
"25(OH)D serum concentrations show a U-shaped risk of prostate cancer suggesting an optimal serum concentration of 40-60 nmol/L for the lowest cancer risk."

Premature aging in vitamin D receptor mutant mice.
"Hypervitaminosis vitamin D(3) has been recently implicated in premature aging... Vitamin D(3) homeostasis regulates physiological aging."

Hypervitaminosis D and premature aging: lessons learned from Fgf23 and Klotho mutant mice.
"excessive vitamin-D activity and altered mineral-ion homeostasis could accelerate the aging process"

Vitamin D, nervous system and aging.
"The relationship of many of these diseases and aging-related changes in physiology show a U-shaped response curve to serum calcidiol concentrations."

Vitamin D: panacea or a Pandora's box for prevention?
"In women from the USA, Finland and China, mortality for 7 types of cancer (endometrial, esophageal, gastric, kidney, non-Hodgkin's lymphoma, pancreatic, ovarian) increases below 45 nmol/L and above 124 nmol/L"

Plasma 25-hydroxyvitamin D and prostate cancer risk: the multiethnic cohort
"a suggestive increased (prostate cancer) risk for higher concentrations 25(OH)D"

Optimal level of 25-(OH)D in children in Nanjing (32°N Lat) during winter.
"The optimal 25-(OH)D level may be (20-24 ng/ml) 50-60 nmol/L for bone health in Nanjing children"

Modelling the seasonal variation of vitamin D due to sun exposure.
"Messages concerning sun exposure should remain focused on the detrimental effects of excessive sun exposure
and should avoid giving specific advice on what might be 'optimal' sun exposure."

What you and your patients need to know about vitamin D.
"current evidence supports the conclusion that protection from UV radiation does not compromise vitamin D status or lead to iatrogenic disease."

Intensity of lipid peroxidation and antioxidant enzyme activity in arterial and venous walls during hypervitaminosis D
"increase in the amount of the intermediate and final lipid peroxidation products has been found in the (blood) vessels of all types".

Serum 25-hydroxyvitamin D3 levels are elevated in South Indian patients with ischemic heart disease.
"Serum levels of 25-OH-D3 above 222.5 nmol/l was observed in 59.4% of cases with ischemic heart disease compared to 22.1% in controls"

Vitamin D, adiposity, and calcified atherosclerotic plaque in african-americans.
"positive associations exist between 25(OH)D and aorta and carotid artery calcified atherosclerotic plaque in African-Americans"

Elevated serum levels of Vitamin D in infants with urolithiasis.
"Serum levels of 25-hydroxyvitamin D3 were significantly higher in the infants with urolithiasis than in the controls (84,6 nmol/L vs 45,7 nmol/L)."

Women's Health Initiative Study
"Long term daily supplementation of calcium with vitamin D ... increased the risk of kidney stones"

[RRM]

The study about lifeguards in Israel (average 148 nmol/L) is particularly interesting.

I agree.
They seem to have a lot more kidney stones than normal... Shabtai M et al
"Eleven of 45 (24%) Lifeguards had proven N (= nephrolithiasis = kidney stones). This is approximately twenty times the incidence of N in the general population". Better OS et al

So, a darker skin protects you against excessive vitamin D production.
Thats what im trying to tell you.

No, a darker skin protects you against excessive UVB exposure.
A white skin protect as good as an black skin against excessive vitamin D production by UVB exposure.
Both skin types show that there is a mechanism which makes sure vitamin D production in the skin is stopped at a certain level.

We have seen healthy, but officially 'vitamin D deficient' people with healthy PTH levels.
We have seen that the cutoff level of 25(OH)D for PTH ranges from being less than 37.5 to 90 nmol / L.
We have seen that those cutoff levels may be 22 nmol / L lower in black people than in white people.
We have seen that with high sun exposure for some 25(OH)D may be 155 nmol, while half of the rest of the participants may still be low on D.
So, there is no such a level.

25(OH)D levels can get too high. (not regarding toxicity, but regarding any adverse health effects)
Elevated serum vitamin D increases calcium absorption (and subsequent excretion) rates, which may result in kidney stones.
Unfortunately, there are no studies about kidney stones in the Maasai and Hadzabe in Tanzania.
(both peoples consume a lot of milk products and have high 25(OH)D levels).
To prevent kidney stones, the body transforms proteoglycans into glycosaminoglycans (GAGs), which inhibit calcium oxalate crystallization,
and reduce calcium oxalate stone formation.
It has been shown that the body excretes about 50% more GAGs in the summer than in the winter. Hesse A et al

With elevated calcium intakes (and due to elevated serum vitamin D in the summer), urine calcium and phosphate excretion is higher in the summer than in the winter. Williams CP et al Urinary calcium excretion is also higher in whites compared to blacks (in the USA) Taylor EN et al, Osorio AV et al
So is the risk of kidney stones in the summer compared to the winter. Cupisti A et al, Baker PW et al, Gluszek J et al, Hesse A et al
("may be due to a relative D hypervitaminosis") Torres Ramírez C et al
The same was concluded in Saudi Arabia al-Hadramy MS and it was also higher in Saudi Arabians compared to immigrants.Khan AS et al
Many of those immigrants have a darker skin, hired to do the dirty work.
"skin pigmentation, assessed by measuring skin melanin content, showed an inverse relationship with serum 25(OH)D". Gozdzik A et al
Living in the same conditions, people with a lighter skin (higher serum 25(OH)D) are more prone to kidney stones than people with a darker skin. Scales CD Jr et al, Akoudad S et al, Rodgers AL et al, Beukes GJ et al, Rodgers AL et al

So, yes, a darker skin is a better protection against elevated serum 25(OH)D.
In as much that a lighter skin is better for preventing too low levels of serum 25(OH)D.

[overkees]

Okay my line of reasoning:

With the fact that darker skinned people (the research I posted on top of this page) tend to have better calcium regulatory systems than white people, I must say that we have looked too much of the research done in the general population.

Darker skinned people were, evolutionary, spending alot of their time in the sun. Sun is good for vitamin D, but bad for the aging of the skin. They needed to get a better protected skin, so they produce more melanin, which is induced by DNA damage in the skin. The side effect of this, is that they make less vitamin D, but that is not a big problem, because they also spend alot of time in the sun.
Vitamin D, however, is needed for calcium regulation. So that in times they aren't spending alot of time outside for a while, they still need to regulate their caclium levels, because melanin stays for quite a while. Therefore, they developped these mechanisms to control calcium better. So they need less vitamin D than white people.
This is the reason alot of the researches state that they are 'deficient'. Because they have other levels needed for vitamin D than white people, who need a higher level.

Therefore we need to focus much more on research done, that takes skin tone in to consideration. So, we need to search for white people's adverse health effects when having too high levels of 25 OHD in the blood. Black people, if I am correct, will have these adverse effects much much faster.

[RRM]

Overkees, did you not read about kidney stones?
There were black people before there were white people. So that this different calcium regulatory system in white people is an adaptation,
compared to the original calcium regulatory system as it functions in black people.
There is another adaptation of white people vs black people; the capacity to cope with lactose in adults.
Both these adaptations were because of white people consuming milk; because of the much higher calcium intakes,
the calcium regulatory system had to be adapted to prevent too high calcium levels.
Because what do elevated calcium levels cause?
Kidney stones.
Sure, instead, white people could have adapted to a way lower vitamin D level (to inhibit stimulus of calcium uptake by vitamin D),
but as Kasper pointed out, we need vitamin D for more reasons than just for calcium uptake.
Hence the 'poorer' calcium uptake by white people independent of vitamin D,
which is therefore an improvement (an adaptation), because it enables maintaining relatively high vitamin D levels while preventing too high calcium levels.

So, when (relatively) white people spend too much time in the sun, their 25(OH)D level will increase too much,
and as white people tend to consume much calcium (drinking milk etc),
this may result in kidney stones, as the studies about lifeguards in Israel show.
In black people spending equally much time in the sun, 25(OH)D (and calcium) levels will be a bit lower, making them less likely to get kidney stones.

So, we need to search for white people's adverse health effects when having too high levels of 25 OHD in the blood.

Kidney stones.
Obviously, serum 25(OH)D in these lifeguards in israel was too high...
We now know when serum 25(OH)D is definitely too high (average 148 nmol/L).

Black people, if I am correct, will have these adverse effects much much faster.

Regarding an increase of PTH, yes, at a lower level.
But, no, they are protected by the color of their skin, so that they will not make as much vitamin D as white people.
Hence less kidney stones in black people (despite efficient calcium uptake independent of vitamin D).