Monday, February 28, 2011

Vitamin D production from UV radiation: The effects of total cholesterol and skin pigmentation

Our body naturally produces as much as 10,000 IU of vitamin D based on a few minutes of sun exposure when the sun is high. Getting that much vitamin D from dietary sources is very difficult, even after “fortification”.

The above refers to pre-sunburn exposure. Sunburn is not associated with increased vitamin D production; it is associated with skin damage and cancer.

Solar ultraviolet (UV) radiation is generally divided into two main types: UVB (wavelength: 280–320 nm) and UVA (320–400 nm). Vitamin D is produced primarily based on UVB radiation. Nevertheless, UVA is much more abundant, amounting to about 90 percent of the sun’s UV radiation.

UVA seems to cause the most skin damage, although there is some debate on this. If this is correct, one would expect skin pigmentation to be our body’s defense primarily against UVA radiation, not UVB radiation. If so, one’s ability to produce vitamin D based on UVB should not go down significantly as one’s skin becomes darker.

Also, vitamin D and cholesterol seem to be closely linked. Some argue that one is produced based on the other; others that they have the same precursor substance(s). Whatever the case may be, if vitamin D and cholesterol are indeed closely linked, one would expect low cholesterol levels to be associated with low vitamin D production based on sunlight.

Bogh et al. (2010) recently published a very interesting study. The link to the study was provided by Ted Hutchinson in the comments sections of a previous post on vitamin D. (Thanks Ted!) The study was published in a refereed journal with a solid reputation, the Journal of Investigative Dermatology.

The study by Bogh et al. (2010) is particularly interesting because it investigates a few issues on which there is a lot of speculation. Among the issues investigated are the effects of total cholesterol and skin pigmentation on the production of vitamin D from UVB radiation.

The figure below depicts the relationship between total cholesterol and vitamin D production based on UVB radiation. Vitamin D production is referred to as “delta 25(OH)D”. The univariate correlation is a fairly high and significant 0.51.


25(OH)D is the abbreviation for calcidiol, a prehormone that is produced in the liver based on vitamin D3 (cholecalciferol), and then converted in the kidneys into calcitriol, which is usually abbreviated as 1,25-(OH)2D3. The latter is the active form of vitamin D.

The table below shows 9 columns; the most relevant ones are the last pair at the right. They are the delta 25(OH)D levels for individuals with dark and fair skin after exposure to the same amount of UVB radiation. The difference in vitamin D production between the two groups is statistically indistinguishable from zero.


So there you have it. According to this study, low total cholesterol seems to be associated with impaired ability to produce vitamin D from UVB radiation. And skin pigmentation appears to have little  effect on the amount of vitamin D produced.

I hope that there will be more research in the future investigating this study’s claims, as the study has a few weaknesses. For example, if you take a look at the second pair of columns from the right on the table above, you’ll notice that the baseline 25(OH)D is lower for individuals with dark skin. The difference was just short of being significant at the 0.05 level.

What is the problem with that? Well, one of the findings of the study was that lower baseline 25(OH)D levels were significantly associated with higher delta 25(OH)D levels. Still, the baseline difference does not seem to be large enough to fully explain the lack of difference in delta 25(OH)D levels for individuals with dark and fair skin.

A widely cited dermatology researcher, Antony Young, published an invited commentary on this study in the same journal issue (Young, 2010). The commentary points out some weaknesses in the study, but is generally favorable. The weaknesses include the use of small sub-samples.

References

Bogh, M.K.B., Schmedes, A.V., Philipsen, P.A., Thieden, E., & Wulf, H.C. (2010). Vitamin D production after UVB exposure depends on baseline vitamin D and total cholesterol but not on skin pigmentation. Journal of Investigative Dermatology, 130(2), 546–553.

Young, A.R. (2010). Some light on the photobiology of vitamin D. Journal of Investigative Dermatology, 130(2), 346–348.

24 comments:

J. A. Deep said...

Any guess as to whether (or why) HDL or LDL, might correlate with Vitamin D production?

Also, does this finding run contrary to the big pharma push to reduce cholesterol with statins?

Great post! I've tried to read extensively on Vitamin D and sun, and would have never guessed at this.

Jake said...

I know that saturated fat consumption is necessary for Vitamin D production as it is for all hormones.

Saturated fat raises HDL and so it would raise total cholesterol.

The correlation then is the lack saturated fat consumption with the lack of Vitamin D production.

I believe the lack saturated fat consumption is one of the main drivers of Vitamin D deficiency in 70% of Americans.

Anonymous said...

Since Vit D production isn't better in light-skinned people, why did lighter skin evolve when people left Africa?

Ned Kock said...

Hi J.A. I think LDL particles play a positive role, as they seem to do also with cardiovascular disease:

http://healthcorrelator.blogspot.com/2010/09/china-study-ii-cholesterol-seems-to.html

It doesn’t look like HDL is the only good guy around, fighting against disease the ravages of the evil LDL particle …

Ned Kock said...

Hi Anon. Perhaps for the same reason that birds evolved all kinds of weird ornaments eh?

Ole Darwin was right about so many things, maybe he got this one right too:

http://www.ncbi.nlm.nih.gov/pubmed/12573076

Ned Kock said...

This may require a separate post, but I should point out that sexual selection is the “venture capitalist” of evolution.

Let’s say a few hundred ancestors reached a new land thousands of years ago. All it would take would be a single high-fertility man to have developed a preference for a trait, by chance, with the trait being coded by a genotype that was also present in female offspring. (This is only one of many possible scenarios.)

As a result, the preference and trait could easily spread to the entire population descending from that initial population. This new population may have grown to millions of people displaying both the preference and the trait.

Fisher was probably the first to fully describe this process mathematically. The process is sometimes called “runaway sexual selection”.

http://en.wikipedia.org/wiki/Runaway_sexual_selection

Runaway sexual selection may even lead to the evolution of traits that are costly. These are traits that impair survival – e.g., the male peacock’s train.

malpaz said...

thats interesting... i get REALLLL tan in the summer with no effort whatsoever on my part and dont really lose it in the winter...but seems it isnt correlated either way with vitamin D level in me. i took vitamin D in the winter this year b/c i get a massive hate for life when it gets cold and it did seem to keep me sane. i still had problems, but no relapse for the first time in like 6 years!

Jack C said...

Ned and Ted,

Great post! Of particular interest to an old guy like me is that there was no correlation between age and delta vitamin D. Fat guys would be interested that no correlation was found between delta vitamin D and BMI. It appears, according to the article, that the decreased vitamin D synthesis from sun exposure that has been attributed to age, obesity and darker skin color is mainly due to sun habits.

I was surprised at their conclusion, based on other studies, that statins do not decrease vitamin D status. Really? That conclusion seems inconsistent with the finding that reduced cholesterol levels result in decreased delta vitamin D synthesis from sun exposure.

The study found that at 56 degrees latitude 30 minutes of summer noontime sun exposure can provide adequate vitamin D. That equates to the sun exposure in mid March at 31 degrees latitude where I live.

I was amused by the fact that the authors, who are dermatologists, do mot recommend sun exposure to maintain vitamin D status because of "cancer risk", but instead recommend vitamin D supplements. That conclusion is expected as they need to keep their jobs!

Ned Kock said...

Thanks Mal for sharing, as always.

Ned Kock said...

Hey Jack, now you know why I like to look at numbers. Sometimes the text entirely contradicts what the numbers say.

Ned Kock said...

Btw, Jack - old guy!? I thought you were a young lad in his 20’s who happened to have a PhD in biochemistry ;-)

Ned Kock said...

Another interesting thing about this article is the use of the term “sun worshippers”. I don’t know if this is common in dermatology research, but it sounds funny to me, especially in an academic journal article.

David Csonka said...

Interesting theory, though there are so many confounding factors it will be hard to determine if it is just the vilification of saturated fat which is the cause, or is it the reduced sun exposure, or decrease consumption of milk for soft drinks, etc.

Helen said...

My cholesterol seems genetically low, which my doctors love (with just the "right" spread between HDL and LDL). I'm soon to find out my vitamin D status. It being early March, this would be mainly from supplementation. Maybe I should wait until the summer for my test, though, to see what I make on my own.

I wonder if those who have less cholesterol need less vitamin D? Any information on this possibility, or is that just wishful thinking on my part? There seem to be ethnic differences between ideal amounts - maybe there are individual differences, too.

Ned Kock said...

Hi Helen. I suggest you wait for the tests and keep in mind that there are major individual variations even in the sample in the study.

Even though TC and delta D are strongly correlated, the second highest delta D in the sample is for a person who seems to be in the first tercile of TC levels. You can see that on the plot of delta D against TC.

Also, since TC is measured after an overnight fast it completely ignores the contribution of chylomicrons. These are lipoproteins that transport some cholesterol from dietary sources to tissues as well, even though their content is mostly triglycerides.

David Isaak said...

"I was surprised at their conclusion, based on other studies, that statins do not decrease vitamin D status. Really? That conclusion seems inconsistent with the finding that reduced cholesterol levels result in decreased delta vitamin D synthesis from sun exposure."

Umm, actually, there has been some speculation that the only benefits of statis are that they somehow preserve or increase Vitamin D levles, and that cholestrol has nothing to do with it.

Google 'statins' "Vitamin D" and 'pleiotropic.'

You can't get at the whole Grimes editorial in the Lancet here, but check out:

http://www.springerlink.com/content/3252535263362294/

It's pretty funny becasue iot casually mentions that no serious researchers any longer accept the cholesterol-heart disease hypothesis, even though it persists in public health and "folklore."

Says it all.

Kris @ Health Blog said...

Vitamin D3 is produced from cholesterol in the skin, I never knew though that low cholesterol levels would actually impair the production of D3.

This is an interesting point and definitely a good argument on one of the shortfalls of having too low cholesterol levels.

PK said...

In regards to sexual selection and skin tone, perhaps it was only when we moved to higher latitudes that the preference for lighter skin could become successful. Perhaps our ancestors in Africa who were born with lighter skin ability to survive long enough to reproduce well were too adversely affected by the inability to block UV rays as much as others. But once migration began, people lighter skin mutations could do fine in the new climate and even be selected for and reproduce more than the average.

Anonymous said...

can u tell me how uv light can effect the vitamin process?

sorry if i'm off the topic. rly curious. help me please? :)

gwarm said...

It looks like DrGreger changed his VitD recommendation from 4000IU/day to 2000IU/day (or 15-30min sun) yesterday:
http://www.facebook.com/NutritionFacts.org/posts/193068787424836

I think these are his studies changing his decision for 20-30ng/ML is safest and not 50-70 for Vitamin D:
http://is.gd/vT4Ogh
from 'too much.pdf'

And he may have seen more in 2011 as these are the 2010 studies.

character limit more...

wedding dresses said...
This comment has been removed by a blog administrator.
Ned Kock said...

Spam comment above deleted.

India Pharmacy said...

The effects of this kind Vitamin D production can be terrible for our body!

EyeWearBuzz said...

UV rays is very harmful to eyes as well! Thanks for sharing this info. Godbless to your blog.