The sun provides one of the best sources of vitamin D. Just 15 minutes of unprotected sun exposure yields up to 10,000 IU or more of this vital nutrient. Sun exposure triggers chemical reactions in the skin that convert vitamin D to a usable form.
This vitamin is critical for calcium absorption, thus its pivotal role in bone health and prevention of osteoporosis. The quandary comes from unprotected time in the sun, i.e., without sunscreen. The same ultraviolet rays that can cause a sunburn are also necessary to stimulate the chemical reactions in the skin.
Finding Other Sources of Vitamin D
The problem is that there are few dietary sources of vitamin D. Healthy dietary sources include salmon, mackerel and sardines, not necessarily the most popular food choices. Egg yolks also contain vitamin D; however, the American Heart Association recommends limiting dietary cholesterol consumption because of possible effects on heart disease risk.
Sun Exposure and Cancer Risk
Ultraviolet radiation includes both UVA and UVB rays. Both have been linked to skin cancer. More than one million new cases were diagnosed in 2010, according to the National Cancer Institute. The concern is that sun exposure for vitamin D may inadvertently be increasing the risk for cancer.
Exposure to UVB rays can damage DNA. Areas of the skin that are regularly exposed to the sun are at the highest risk. To decrease the risk, sun exposure must be limited or a suitable sunscreen applied prior to exposure. Sunscreen will block UVB rays, the same rays that help the skin produce vitamin D. The paradox however, does not end here.
Vitamin D and Cancer
Research has yielded an interesting contradiction regarding vitamin D and cancer. Cancer varies with the type. Each one may have certain environmental and genetic triggers. Cigarette smoking, for example, leads to lung cancer.
Circumstantial evidence exists that inadequate intake of vitamin D can increase the risk for certain types of cancer including colon cancer. A 1999 study by the University of California found evidence of rickets history coincided with the incidence of colon cancer. Rickets describes a condition caused by a vitamin D deficiency. A similar association was found between breast cancer and vitamin D.
Changes in Vitamin D DRI
While the scientific evidence is mixed and still emerging, enough compelling research fueled the change in the dietary reference intake by the Institute of Medicine from the previous 400 IU to 800 IU for adults until age 51 in 2010. The DRI for adults over 51 years of age is 1,000 IU.
Caution is necessary when taking a vitamin D supplement. If the body absorbs too much calcium, the risk for kidney stones and calcification of heart and lung tissue exists. Blood levels of vitamin D can be determined through a simple blood test to monitor intake.
The role of the sun in vitamin D synthesis shows how humans have evolved with the conditions of their environment. The need for sun exposure shows the vital role in plays in good health. However, because of its risk, sun exposure remains a double-edged sword when it comes to cancer prevention. In the end, an individual's health status and genetic history may have the final say on what is appropriate and safe.
Sources
Drugs: Vitamin D drugs.com
Garland, C., et al. (1999). Calcium and vitamin D. Their potential roles in colon and breast cancer prevention. Annals of the New York Academy of Sciences, 889:107-19.
Grant, W. (2002). An ecologic study of dietary and solar ultraviolet-B links to breast carcinoma mortality rates. Cancer, 94(1):272-81.
Linus Pauling Institute: Vitamin D lpi.oregonstate.edu
