Sun exposure may give skin an attractive glow, but it also damages skin and causes skin cancer. Yet your body needs sunlight to produce vitamin D, an essential nutrient for healthy bones and the immune system. Too little time outside and heavy sunscreens that prevent the skin from absorbing sunlight may help prevent wrinkles and skin cancer but may also lead to vitamin D deficiency.
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Vitamin D maintains proper calcium levels in the body. The bones, nervous system and immune system depend on calcium for proper functioning. Without vitamin D, the body is unable to absorb and use calcium efficiently. Vitamin D deficiency weakens bones and leads to osteoporosis and rickets. People with vitamin D deficiency are prone to infection because of a poorly functioning immune system and are at an increased risk for cardiovascular complications.
Vitamin D and Sun
Your body manufactures vitamin D in a three-step process. The ultraviolet, or UV, radiation from sunlight stimulates skin cells to produce vitamin D precursors. The liver converts these precursors to calcidiol, which the kidneys change into the active form of vitamin D that the body can use. You may also obtain vitamin D through diet, although few foods naturally contain vitamin D.
Sunscreens block UV rays from penetrating the skin and damaging cells. Sun protection factor, or SPF, measures the amount of sun protection offered by sunscreens and sunblocks. The SPF number represents the amount of time the average person using the sunscreen can spend in the sun without being burned, compared with someone using no sun protection. The higher the SPF, the greater the protection and the longer you can remain outside without risking a sunburn.
SPF and Vitamin D
A high SPF not only prevents UV rays from damaging the skin, but it also prevents the absorption of vitamin D from sunlight. Using sunscreen with an SPF of 8 cuts the amount of vitamin absorbed from the sun by 95 percent, and those with higher SPF rates reduce vitamin D absorption to virtually zero. Skin protection offered by sunscreens offsets the risk of vitamin D deficiency caused by too little sun exposure. When sun exposure is limited or blocked with high-SPF sunscreens, dietary vitamin D intake must increase to compensate for the lack of the vitamin absorbed from sunlight.
Only 10 to 15 minutes of sun exposure daily provides adequate levels of vitamin D. People who stay indoors, wear high-SPF sunscreens or have dark skin pigmentation may not absorb enough vitamin D from sunlight and may be at risk for vitamin D deficiency. These people should increase their dietary vitamin D. Fish oil and fatty fish such as salmon and tuna contain the highest amounts of naturally occurring vitamin D, with smaller amounts found in egg yolks, beef liver and cheese. Dietary vitamin D is also found in fortified foods, such as milk, orange juice and breakfast cereals, and nutritional supplements. According to the American Academy of Dermatologists, getting vitamin D from supplements is preferable to synthesis in the skin from sun exposure.