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Soak Up Vitamin D While You Still Can!

vitamind-heartAs summer begins its inevitable dwindle into cooler nights and shorter days, it’s easy to forget that the sun’s potency is in full swing well into the fall. As your mind wanders watching the kids play soccer, you may find yourself wondering, how much sun is too much?

Vitamin D is a unique nutrient, as it is formed in the skin by UV light. Most tissues in the body including brain, skin, breast, prostate and colon have Vitamin D receptors. Vitamin D deficiency is important for healthy bone metabolism, and decreased levels are associated with an increased risk of hypertension, autoimmune disorders including Type I Diabetes, and an increased risk of mortality from breast, colon, ovarian and prostate cancer.

Additionally, Vitamin D is a necessary nutrient for the production of the neurotransmitter serotonin. In women with PCOS, low levels of Vitamin D are associated with obesity as well as metabolic and endocrine disturbances. Vitamin D stimulates the expression of insulin receptors, contributing to balanced blood glucose levels which play a role in healthy hormone metabolism for men and women.

Unfortunately, the UV light that provides the vitamin so essential to human health can also dramatically increase the risk of skin cancer at larger doses. So how do we know how much is too much?

The answer, as you might expect, depends on each individual skin type, as well as latitude and time of year. Establishment of the minimum erythemal dose (MED), the minimal amount of sun exposure required to cause redness in the skin, can be a good indicator for some people, however there is evidence that this measurement is significantly less accurate in darker skin types. Once an individual’s MED is known, exposure of the face, arms, hands and legs for 20-25% of that time should provide an adequate vitamin D dose. For example, if one develops a mild sunburn after 30 minutes of exposure, then exposure for 20-25% of that time (ie.: six to eight minutes) two to three times per week is adequate to satisfy the body’s vitamin D requirement. Keep in mind however that during the winter months at latitudes above the 35 parallel the sun is not at a sufficient angle to provide the adequate UV exposure. In some locations, this results in a short window of opportunity to produce vitamin D in the skin, and often inadequate stores of vitamin D to last throughout the winter.

However, skin cancer is the most common form of cancer found in the US, and the largest controllable risk factor is sun or UV exposure. Long-term exposure to the sun, and allowing the sun to burn, can dramatically increase the risk of all forms of skin cancer. For this reason, the use of sunscreen has become widespread. Unfortunately, a sunscreen with an SPF of only 8 reduces the ability to produce vitamin D by 97.5%! Many sunscreens also contain xenoestrogens and other endocrine disrupting chemicals which are readily absorbed via the largest organ of the body, the skin. To find out how toxic or safe your sunscreen is, refer to the Environmental Working Group’s Guide To Sunscreens.

What to do? As with many things, the most reasonable way to navigate the vitamin D/sun exposure/skin cancer debate is to take heed of your individual MED to ensure judicious Vitamin D absorption, covering up before the skin starts to pink, using long sleeves and sunshades rather than sunscreen when available, and measuring serum vitamin D levels in the fall to ensure that stores are adequate before winter. If serum levels are insufficient, supplementation is warranted regardless of the season.LabrixLogo


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  • National Cancer Institute. What You Need to Know About Skin Cancer. Bethesda, MD: National Institutes of Health, U.S. Department of Health and Human Services.
  • R. P. Patrick, B. N. Ames. Vitamin D hormone regulates serotonin synthesis. Part 1: relevance for autism. The FASEB Journal, 2014; DOI: 10.1096/fj.13-246546
  • Hoseini SA, Aminorroaya A, Iraj B, Amini M. The effects of oral vitamin D on insulin resistance in pre-diabetic patients. Journal of Research in Medical Sciences : The Official Journal of Isfahan University of Medical Sciences. 2013;18(1):47-51.

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