Explain the potential difficulties in obtaining the recommended amounts of vitamin D from the sun.

Question

What will be an ideal response?

Answer 1

Most of the world’s population relies on natural exposure to sunlight to maintain adequate vitamin D nutrition. The sun imposes no risk of vitamin D toxicity; prolonged exposure to sunlight degrades the vitamin D precursor in the skin, preventing its conversion to the active vitamin.
Prolonged exposure to sunlight can, however, prematurely wrinkle the skin and cause skin cancer. Sunscreens help reduce these risks, but sunscreens with a sun protection factor (SPF) of 8 and higher can also reduce vitamin D synthesis. Still, even with an SPF 15 to 30 sunscreen, sufficient vitamin D synthesis can be obtained in 10 to 20 minutes of sun exposure. Alternatively, a person could apply sunscreen after enough time has elapsed to provide sufficient vitamin D synthesis. For most people, exposing hands, face, and arms on a clear summer day for 5 to 10 minutes two or three times a week should be sufficient to maintain vitamin D nutrition. Avoiding sun exposure completely may be harmful to health.
The pigments of dark skin provide some protection from the sun’s damage, but they also reduce vitamin D synthesis. Dark-skinned people require more sunlight exposure than light-skinned people—perhaps as much as 4 to 6 times longer. Latitude, season, and time of day also have dramatic effects on vitamin D synthesis and status. Heavy cloud cover, smoke, or smog block the ultraviolet (UV) rays of the sun that promote vitamin D synthesis. People who stay in the shade and wear long-sleeved clothing are twice as likely to develop vitamin D deficiency as those who rarely do so. Vitamin D deficiency is especially prevalent in the winter and in the Arctic and Antarctic regions of the world. To ensure an adequate vitamin D status, supplements may be needed. The body’s vitamin D supplies from summer synthesis alone are insufficient to meet winter needs.
Depending on the radiation used, the UV rays from tanning lamps and tanning beds may also stimulate vitamin D synthesis. The potential hazards of skin damage, however, may outweigh any possible benefits. The Food and Drug Administration (FDA) warns that if the lamps are not properly filtered, people using tanning booths risk burns, damage to the eyes and blood vessels, and skin cancer.