At this point, it’s probably safe to say that we simply do not know how much sun early man got.
With this in mind, isn’t it a bit less plausible that, when it comes to the ability of the human body to naturally adjust its vitamin D levels for optimal health, current humans are a complete evolutionary bust and must be given truckloads of pills in order to remain healthy?
Dr. Michael Holick speaks on sunscreen and vitamin D
Dr. Michael Holick is a professor at Boston University, a medical doctor, and may be the world’s leading authority on vitamin D.
Since 2005, he has authored or co-authored 59 publications appearing in PubMed on vitamin D (26 more than Dr. William Grant, who is second in that category and a frequent co-author) and he has the distinction of being quoted on vitamin D in nearly every magazine, newspaper, television show and website ever.
In his 10-minute statement, Dr. Holick was critical of dermatologists, a group which he singled out for advising the public to avoid creating vitamin D by direct sun exposure. As it happens, Dr. Holick receives large amounts of funding from the UV Foundation, which is in turn
sponsored by the Indoor Tanning Association.
Entitled
The D-Lightful Vitamin for Health, Dr. Holick remarks sprinkled his speech with a number of pop culture references including mentions of Charlie Brown and Don King. And then there was the clip of Darth Vader telling Luke to come to the Dark Side. It has been a while since we have seen the Star Wars trilogy, but we don’t seem to recall Darth Vader’s evil stemming from his unnecessary prudence.
Dr. Holick went on to claim that sunscreen use blocks 99% of vitamin D production in the skin. This claim is a featured part of his argument, because there has to be a reason why what he views as vitamin D deficiency is so widespread. If there’s evidence to back up this statistic, then our search of the literature cannot find it.
What we did find were three small studies, one of which Dr. Holick authored himself.
One of these studies measured the vitamin D3 (a precursor of 25-D) levels of only eight subjects
[10] while
another performed no intervention but simply measured the 25-D levels of 20 sunscreen users.
[11]
The
third put only 27 subjects into tanning beds rather than into the sun, which could easily introduce bias.
[12] All three are by the same lead author, Dr. Lois Y. Matsuoka.
As it happens, several reviews have refuted the idea that real-world use of sunscreen entirely halts cutaneous production of vitamin D.
By real world, we mean people putting sunscreen on themselves for extended periods of time while exposed to the actual sun.
Dr. William L. Scarlett writes in
his review, “Several large
prospective studies have shown that vitamin D deficiency does not result from regular sunscreen use.”
[13]
One research team, studying patients with xeroderma pigmentosum, a genetic disorder in which patients are unable to repair damage caused by ultraviolet light,
found that vitamin D levels are maintained even when patients practice at least six years of rigorous photoprotection and not supplementing with vitamin D beyond their normal dietary intake.
Most importantly, the researchers also concluded that the clinical manifestations of vitamin D “deficiency” were absent.
In a
2007 review, Dr. Melanie Palm concludes real-world people tend not to consistently or repeatedly apply sunscreen.
[15] She writes: “Most people’s real-life experience with sunscreen is that despite its application, they still sunburn or tan after casual sun exposure.”
Dr. Palm goes on to explain, “
SPF [sun protection factor] is a strictly defined and Food and Drug Administration (FDA)-regulated measurement based on applying 2 mg/cm
2 of product.
Studies have shown that most users apply insufficient amounts of sunscreen to meet this FDA standard, and the true SPF obtained is usually less than 50% of that written on the package.”
Dr. Holick also proudly informed the committee of the manner and amount of his vitamin D intake. If you ask us, this is irrelevant.
It’s nice that Dr. Holick believes what he says enough to try it on himself, but this kind of data falls to the very bottom of Dr. Kramer’s evidence-based pyramid – the opinion level that should never be used to guide public health decisions.
In the remainder of his talk, Dr. Holick went on to say that no one living in a latitude north of Atlanta, Georgia can make vitamin D in their skin during the winter months. Based on everything else we have heard, maybe you can understand why we’re a bit dubious of this claim.
It seems that one of the unspoken rules of publishing a study on vitamin D is that you must cite Michael Holick – geez, even
we have done it. But in light of the conflicting data related to Dr. Holick’s claims, we have to wonder why the man has been accorded that authority and why more people don’t second-guess some of his more definitive statements.