I went to my dermatologist last week for my yearly checkup, an experience almost as pleasant as my semiannual trip to the dentist. I got checked over and we had a distracting conversation while he did his thing. On the way out he gave me some paper instructions and an interesting flier that is the topic of this post. I have attached it below. It is titled SUNSCREEN RECOMMENDATIONS and has this recommendation, “Boone Dermatology Clinic recommends daily sunscreen use for all patients over the age of 6 months. We recommend a broad-spectrum sunscreen with a minimum of SPF30.” It is important to notice how inclusive this is: everyone over 6 months with no exceptions, broad spectrum for all wavelengths, a SPF30 so that it is a complete blockage, and daily use with no exception for season or weather or time of day. This apparently means all day. Here is my problem with this statement as a nutritionist. This pretty much guarantees that all their patients will be vitamin D deficient.
Here is what pretty much any textbook will tell you about vitamin D. We get most of it from the sun. It is called the sunshine vitamin for a reason and is barely even a vitamin in the usual sense. The same UV radiation that gives you sunburns allows you to make vitamin D in your skin. But any SPF greater than about 6 completely blocks vitamin D synthesis in the skin. We only get the right UV from the sun between about 10AM and 3PM. All latitudes north of about 35 degrees (think Atlanta, Georgia) is too far north to get sufficient vitamin D from our usual exposure to the sun. Most Americans get almost no vitamin D from the sun in the winter both because the sun is too low and because we are so covered up. Just imagine what this says about the vitamin D status of Canadians. About 15 minutes in the full summer sun with bare arms and face will give most folks enough vitamin D for most of a week. As a rule of thumb, if you aren’t worried about getting a sunburn, then you aren’t getting vitamin D.
Vitamin D deficiency is surprising common around the world, with about a billion people affected. People who tend to stay out of the sun, people with darker skin, people north of Atlanta, and older people are all affected. There is a threshold for sun exposure. A sunbather on a sunny day in January in Boston could stay out all day and apart of the frost bite, would gain no vitamin D benefit.  But, a White person exposing only arms and legs, thinks short and a tee, need only stand in the Texas sun for 15 minutes for all the vitamin D for a couple weeks. A Black person would take about three times as long.
Now my dermatologist will counter that it would be so much easier and safer if we all just took a vitamin D supplement, and this is true. So, the full recommendation is to slather every citizen every day all day with sunscreen and also take a vitamin pill every day. How about this as an alternative? Don’t worry about the sun for 3 seasons of the year if you live north of Atlanta. In the summer, wear comfortable clothes and wait 15 minutes (if you are White and longer if you are Black) before putting on sunscreen in exposed areas. Easy to remember and will save you gallons of sunscreen.
The real issue here is the balance between the risks of melanoma, a very lethal skin cancer that is greatly enhanced by excess UV exposure, and the risks associated with vitamin D deficiency. Yes, the risks of melanoma are real. Recent data show that in the US there are about 106,000 cases annually with about 8,000 deaths. This makes it the 12th most lethal cancer in the country. Compare this to lung cancer with 235,760 cases and 131,880 deaths. In contrast to the effect of UV rays on melanoma, research has shown a strong possible role for vitamin D deficiency in breast cancer risk. A recent meta-analysis combining 22 studies showed that women with vitamin D deficiency had 91% increased odds of having breast cancer. Those that said they took supplements had a 3% decreased risk. So much for supplements.  In fairness, another similar study of supplements and breast cancer mortality showed a 14% reduction with vitamin D supplements.  The same study showed no effect on overall mortality. Others have found roles for vitamin D in possibly preventing colon cancer, prostate cancer, and lung cancer. If vitamin D can reduce the risk of these four big killers by only a small fraction, this might easily balance the effect of UV on melanoma. A recent meta-analysis of vitamin D clinical trials suggests that supplements may cause about a 20% reduction in overall cancer mortality. 
Now this may sound like I am an apostle of vitamin D. Not so. I have been around the field of Nutrition long enough to see things come in and out of vogue. Vitamin D was hot when we nutritionists and many in the general public thought it would prevent or cure everything from lupus to hangnails. That day has passed and a more sober view is setting in. Notice that I did not make any claims for vitamin D and COVID or for immune function. These are rather dubious claims. Even the 20% cancer reduction that I quoted above has been challenged. 
So, should we slather and supplement or just delay slathering and only in the summer? From the public health perspective, I think delaying in the summer is the better message because it has the added advantage of getting people outdoors where they can play, exercise, breath fresh air and lower risk of COVID. Some have suggested that insufficient sunlight is responsible for about 400,000 deaths per year in the United States.  While I personally think this may be an overestimate, it is interesting to compare this to the 8000 known melanoma deaths per year and the slather and supplement regimen my dermatologist recommends to prevent them.
Looks like I may need to have a talk with my dermatologist.
1. Hollis, B.W., Circulating 25-Hydroxyvitamin D Levels Indicative of Vitamin D Sufficiency: Implications for Establishing a New Effective Dietary Intake Recommendation for Vitamin D. The Journal of Nutrition, 2005. 135(2): p. 317-322.
2. Hossain, S., et al., Vitamin D and breast cancer: A systematic review and meta-analysis of observational studies. Clin Nutr ESPEN, 2019. 30: p. 170-184.
3. Zhang, Y., et al., Association between vitamin D supplementation and mortality: systematic review and meta-analysis. Bmj, 2019. 366: p. l4673.
4. Mahendra, A., et al., Vitamin D and gastrointestinal cancer. J Lab Physicians, 2018. 10(1): p. 1-5.
5. Trump, D.L. and J.B. Aragon-Ching, Vitamin D in prostate cancer. Asian J Androl, 2018. 20(3): p. 244-252.
6. Wei, H., et al., Associations of the risk of lung cancer with serum 25-hydroxyvitamin D level and dietary vitamin D intake: A dose-response PRISMA meta-analysis. Medicine (Baltimore), 2018. 97(37): p. e12282.
7. Manson, J.E., S.S. Bassuk, and J.E. Buring, Principal results of the VITamin D and OmegA-3 TriaL (VITAL) and updated meta-analyses of relevant vitamin D trials. J Steroid Biochem Mol Biol, 2020. 198: p. 105522.
8. Manson, J.E., et al., Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease. N Engl J Med, 2019. 380(1): p. 33-44.
9. Alfredsson, L., et al., Insufficient Sun Exposure Has Become a Real Public Health Problem. Int J Environ Res Public Health, 2020. 17(14).
5 thoughts on “Dermatology vs. Nutrition, the Case of Vitamin D”
Thanks so much for sharing, Marty! Thank you for your sources as well.
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Thanks Marty. I am going to print this and bring it to my dermatologist. Since I am a melanoma “survivor” I get to have those check ups more often. Your argument seems reasonable, I can sit in the sun ( in the summer) for a few minutes before putting on sunscreen and not burn. The trouble comes when I then forget to go put it on.
Yes, forgetting is a problem. For folks in the northern latitudes, a vitamin D supplement in winter is probably not a bad idea. I take one.
Wow! What a great blog!!!! Thrilled you are doing this Marty. I have a new “go to guy” for science! My first read is on Vitamin D which is a big issue in my life. Thanks so much!
Everyone who is retired and has something to say could have a blog. Great fun.