Chasing the Sun

Back in the day, working on the gym floor, I used to love it when body building season came around as we would get the best baking brought into the gym by those on their chicken and broccoli diets.  The more the diet was biting them, the more obsessed they would become with food and the more they would bake.  And of course, because they couldn’t eat what they had made (in theory), us non-body building PT’s benefitted.  Which may have gone some way, at least, in explaining the good set of kidney warmers I was building up at the time…

Now, as we approach our shortest day, I can somewhat understand the mindset of those dieters.  It has been nearly two weeks since we have had any real prolonged bright light here in Christchurch and I find my mood slipping as low as the sun in the sky.  The less sun we have had, the more I have pined for it, and the more I have been reading and writing on aspects of sun exposure.  Writing about the sun seems to have become that tray of muffins that the dieters could never have…

 

Reports such as this one suggesting that populations in our (relatively sunny) region have impaired vitamin D status, and this one going some way to explaining why this might be the case, vitamin D insufficiency seems to be increasingly common.  One of the commonly held ‘just so’ stories that go along with sun exposure and vitamin D production is that those with darker skin pigmentation have lower vitamin D production rates.  But a 2010 paper on the topic challenges this.  It also underscores the common link between vitamin D and cholesterol, which I touched on in a previous post on cholesterol and heart disease.

Vitamin D production after UVB exposure depends on baseline vitamin D and total cholesterol but not on skin pigmentation.

The authors of this paper looked at three different groups.  The first group of 50 subjects had their vitamin D production response measured, after exposure to UVB radiation, with a wide range of starting baseline levels.  What they found, unsurprisingly, was that the less 25(OH)D you are starting with, the more responsive you are to UVB radiation exposure.  Conversely, the more you had at baseline, the less you made with UVB exposure.  Sounds like a classic regulatory mechanism to me.  Perhaps one that we override when we take oral vitamin D supplements…

As this first group contained individuals with varying amounts of previous sun exposure, the authors sought to measure the response amongst a smaller group of non-sun worshippers.  Amongst this group of 28, skin pigmentation – either the baseline pigmentation or the pigmentation induced by tanning – did not have any effect on 25(OH)D levels.  However, baseline cholesterol levels did.  This is again unsurprising as vitamin D is, for intent and purposes, produced from cholesterol…

Notably, we also found a significant positive relation between D25(OH)D and baseline total cholesterol levels. The synthesis of vitamin D starts in the bowel epithelial with the oxidation of cholesterol from food or bile to pro-vitamin D3 (7-dehydrocholesterol), which is then transported to the skin, mainly the epidermis, wherein it is isomerized to pre-vitamin D3 (cholecalciferol) by UVB radiation.

Following from the above, the authors make an interesting observation with regard to statin therapy…

A recent study also reports a significant positive relation between baseline vitamin D and total cholesterol level. However, there is no indication of a fall in vitamin D status after statin therapy. Statin therapy inhibits the enzyme hydroxymethylglutaryl-CoA (HMG-CoA) reductase, which is believed to increase the level of 7-dehydrocholesterol, a precursor of vitamin D.

Which begs the question, is any of the benefit obtained from statin therapy (albeit in a narrow band of the population), related to their ability to increase vitamin D precursors rather than any specific cholesterol-lowering effect?  Is it just adding to the diversion of cholesterol precursors toward vitamin D production?

The final group studied here consisted of nine matched pairs of dark and fair-skinned individuals whose baseline 25(OH)D levels were identical.  Despite significant differences in skin pigmentation levels, no significant differences in 25(OH)D were seen, showing that 25(OH)D production is unrelated to skin pigmentation and supporting similar findings from previous research.

So what might explain the lower vitamin D status of dark-skinned individuals compared to fair-skinned individuals?

…it might be possible that vitamin D insufficiency among certain ethnic groups results from other factors than skin pigmentation such as behavior or diet.

We found a remarkable difference in sun habits between the dark-skinned group, who were non-sun worshippers with limited levels of sun exposure, and the fair-skinned group, in which the main part was sun worshippers with excessive levels of sun exposure. These differences in sun habits may explain why dark-skinned persons are reported to have lower vitamin D levels than fair-skinned persons.

Based on the above, it would seem that dark-skinned individuals exhibit different behavioural patterns around sun exposure, sheltering from the sun rather than being out amongst it like their fair-skinned counterparts.  The exposure levels of dark-skinned individuals living in equatorial regions, eating a traditional diet, may well be enough to hold vitamin D levels up at sufficient levels.  But place dark-skinned individuals, who may well tend to naturally avoid the sun, at more northern/southern latitudes, in combination with a change in dietary patterns, and this may be the drivers for the differences in vitamin D status rather than the skin pigmentation per se.

Overall this was a good study, emphasising the need to have the basic building blocks in place (cholesterol, a healthy gut, and sufficient UVB exposure), in order to make sufficient vitamin D.  It wouldn’t be too much of a stretch to suggest that if any combination of those basic building blocks weren’t in place, with gut health being a particularly intriguing part of the picture, that vitamin D status is likely to be impaired.

Our study shows that both fair-skinned and dark-skinned persons without any underlying medical condition should be able to produce sufficient vitamin D from a few low doses of UVB (…equivalent to ~30 minutes of sun exposure in the middle of a clear summer day in Denmark, 561N)…

…we found that baseline vitamin D level is an important determinant of vitamin D production after UVB treatment. We also found that constitutive or facultative skin pigmentation in winter is of no importance for the vitamin D production in the skin. Furthermore, this study revealed a relation between total cholesterol and vitamin D production, indicating that a low natural cholesterol level might be problematic.

However, this paper wasn’t without its WTF? moment…

…due to its skin-carcinogenic effect, we would not recommend UVB treatment to be used as a source of vitamin D to the general population, because sufficient vitamin D levels can be re-established with vitamin D supplements.

Head.Bang.Desk.Repeat.

8 thoughts on “Chasing the Sun

  1. Pingback: Chasing the Sun | THAT PALEO GUY | Primal in Poole

  2. Richard

    I am a naturally very white skinned person living in the tropics (about 10 degrees north…) , and the last time I checked I had Cholesterol level of 245, with LDL at about 170 and Triglycerides of about 70… So lately I have been doing my sun exposure on a regular basis but about all I can handle is 10 minutes. It’s not just hot and sticky, it’s incredibly intense.

    In any event, I’m not distressed with the levels, but it does raise an interesting point, about what a person’s body is trying to do with cholesterol production, and why.

    I also think that you may miss the point that many people here, with beautiful colored skin, sort of medium brown, want to be white and avoid the sun like the plague. They want to be white. They take glutathion to get white and stay inside during the day. The idea of deliberately exposing yourself to the sun is just not considered.

    And cancer and diabetes are rampant.

  3. Louise Baker

    Awesome post! And great song. Wasn’t today just the biggest relief; seeing the sun again made me feel 100x better than I have for weeks!

      1. Louise Baker

        Yep, Mr 4 and I had a leisurely Paleo picnic in the sun on the balcony. Bliss! (Although strictly speaking I suppose carrots dipped in Marmite isn’t Paleo, lol.) Just the relief of being outside without a winter coat for a few hours was restorative.

  4. Alex J

    Interesting. If cholesterol is essential for vit D formation, do you think that FH might have been adaptive for more sun-deprived populations?

  5. Pingback: La Revue du Net Paleo #3 | Paléo Lifestyle: Manger et Vivre Paléo

  6. Cassiel

    The final paragraph (and your response) reminds me of an interview I read awhile back. It was with a guy who’d done really definitive studies into the importance of B12 in the diet and was advocating supplementing. The interview was filled with really complicated sciencey stuff that made my head spin, but was really interesting. The guy obviously knew his stuff and had smarts. Then right at the end, the interviewer asked if people should get their B12 from their diet instead of supplements. The guy replied, and I believe this is almost word for word, “no, because you get B12 from meat and meat is bad for you”. I nearly had a literal headdesk moment. XD

    Really enjoying your sun posts lately, by the way. We’re not getting enough sun here in Sydney, either, particularly with all the rain lately, and I sorely miss it!

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