The sun, your skin, and Vitamin D

What about the sun’s beneficial effects?  The sun plays a major role in the body’s synthesis of vitamin D.  Ultraviolet B radiation is absorbed in the epidermis where 70% of previtamin D is synthesized.  Almost 100% of the previtamin D is converted to vitamin D within 4 hours of sun-exposure.  So, how much sun is required, and could strict sun avoidance lead to vitamin D deficiency? 

As an aside, it should be noted that vitamin D synthesis also requires adequate dietary calcium intake.  The Minimal Erythema Dose, or MED is the amount of ultraviolet radiation, specifically UV-B for vitamin D metabolism that will cause redness of the skin.  Even if only 6% of the skin’s surface were exposed to only 1 MED, the body would be able to produce the equivalent of 600-1000 IU of vitamin D. 

How does this translate to real life practices?  The good news is that we do not need to experience redness or a sunburn to have adequate vitamin D metabolism.  Sub-erythemal sun exposure of the hands, face, and arms a mere 2-3 times per week is more than adequate.  90-95% of people obtain their vitamin D requirement from casual sun exposure.  This is often enough, even for people who live in climates where they can only make vitamin D in the spring, summer, and fall.   The reason is that vitamin D is fat-soluble and can therefore be stored in the fat and released when needed. 

Should we be concerned that strict sun avoidance and sunscreen use will cause vitamin D deficiency?  The answer is NO!  If the above statistics are not proof enough, most people do not ALWAYS use sunscreen before going outdoors, nor do they use the proper amount.  So again, incidental sun exposure in the spring, summer, and fall is more than adequate. 

Kenneth Mark, M.D.
Kenneth Mark Skincare, Inc.

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