Sunscreen Use and Vitamin D
A number of you have mentioned to me that the reason you do not use sunscreen is because you do not want to block vitamin D production in your skin. In fact, if you expose your skin to 20-30 minutes of sunshine 3 times a week, this is more than enough sun exposure to provide adequate vitamin D levels. Also, thesurface area ofskin that needs to be exposed to the sun to provide an adequate vitamin D supply does notneed to be much larger than the surface area of your forearms. Therefore, it is irrational to remove most of your clothing and lie in the sun for several hours to stimulate vitamin D synthesis. Cutaneous vitamin D production is limited to 10-20% of the original epidermal 7- dehydrocholesterol (pre-vitamin D3) concentration. Additional UVB transforms skin pre-vitamin D3 into inactive metabolites; namely tachysterol and lumisterol. However, UV damage of skin cells increases linearly with continued exposure.
It does not make good sense to engage in a behavior that will potentiate the development skin cancer and rationalize that it will be good for your bones. Would you start smoking so you can stay thin?
Studies have shown that vitamin D supplements are perfectly acceptable solution to maintaining healthy vitamin D levels. Current recommended doses are 400-2000 international units per day, depending on one's age and skin type. Dietary sources of vitamin D include milk, salmon, tuna, sardines, mackerel, and fortified orange juice. To fulfill a daily requirement of vitamin D 1000 IU, you need to drink 10 eight oz. glasses of milk or eat 3 servings of salmon daily. Your vitamin D level can be measured by blood test, to determine if you need to take supplementation.