But there is a "healthy" aspect to our skin's absorption of the sun's ultraviolet (UV) rays. It's called vitamin D synthesis. The UV rays from the sun catalyze a chemical reaction in our bodies to synthesize an inactive form of vitamin D. This inactive variation of vitamin D is then converted by our kidneys to the active, more usable form. This active form is what helps our bodies to absorb calcium from the small intestine and deposit it into our bones and teeth. The suggested amount of vitamin D intake for infants, children, teens, and adults is 50 to 200 international units (IU). Adults 51-70 should increase their intake to 400 IU and older individuals are recommended to take 600 IU. This equates to about 5, 10, 15 micrograms (mcg). But don't be fooled into thinking that you need lots of sun exposure to get your vitamin D. You only need about 10-15 minutes, three times a week in the United States. Other parts of the world will vary in UV intensity, making appropriate exposure time in the US inappropriate elsewhere. Be sure you check your location's UV intensity levels before making your outdoor plans. If you can't get outside in the sunshine, try supplements or foods that contain vitamin D.
The unhealthy aspect of UV rays is the threat of skin cancer. There are three types of cells that develop skin cancer: basal cells, squamous cells, and melanocytes. Basal and squamous cell cancers occur on skin that's been exposed to the sun over a cumulative period of time and mostly affects people with light skin and eyes. Naturally darker skinned people may be less susceptible to burning, since their pigmentation may block up to 95% of UV rays emitted. This doesn't eliminate the risk of skin cancer, though. For those who are naturally fair haired and light-eyed, tanning and burning will not only damage your skin immediately, it may increase your risks for skin cancer. Remember that the effect of skin cancer is cumulative, which means that skin damage builds up year after year.
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