Getting enough vitamin D can significantly reduce the risk of several different types of cancer, and ecological studies done over the past decade have confirmed that sun exposure is a critical source of this vitamin, according to a recent report in Annals of Epidemiology.
Researchers have been looking at the connection between vitamin D from sunlight and cancer risk since 1980, when researchers Cedric and Frank Garland looked at geographic maps of cancer deaths and found that mortality from colon cancer was highest in places where residents got the least amount of sun exposure (such as in high latitudes).
William B. Grant, PhD., Director of the Sunlight, Nutrition, and Health Research Center (SUNARC) in San Francisco, California, has been one of the foremost researchers on vitamin D and cancer incidence since 2000. In a 2002 study, he identified 14 different types of cancers that were linked to insufficient UVB exposure, and estimated that between 17,000 and 23,000 people die prematurely each year in the U.S. due to a lack of vitamin D from the sun.
The strongest associations between vitamin D from the sun and cancer have been with colon and breast cancers, but links have also been found with non-Hodgkin lymphoma, ovarian cancer, and kidney cancer. Studies have also connected vitamin D to a reduced incidence of other diseases, such as colds and flu, coronary heart disease, stroke, and congestive heart failure.
People can get vitamin D in two ways: from the diet (in foods such as salmon, milk, and eggs) and through sunlight exposure (the skin produces vitamin D when exposed to the sun’s UVB rays). Yet diet supplies only about 200 to 300 IU of vitamin D each day; a fraction of the recommended dose for cancer prevention, according to Dr. Grant. “The amount of vitamin D in diet is just not sufficient to have an impact, he says.
The sun is a much more potent source of vitamin D. “In the United States in the summer, people can make 1,500 IU of vitamin D just from casual [sun] exposure,” Dr. Grant says. For people who are relatively young, as little as five to 10 minutes of midday sun exposure without sunscreen is enough to produce the 4,000 IU of vitamin D he recommends daily for disease prevention. Those who are over age 60 may need to spend a few extra minutes outside each day because their bodies don’t produce the vitamin as efficiently.
Despite the mounting evidence that a few minutes of daily sun worshipping is good for the health, dermatologists and cancer investigators have been at odds when it comes to sun advice. For years, dermatologists have been warning Americans to stay out of the sun when possible, and to wear sunscreen when exposed, to avoid developing melanoma—the deadliest form of skin cancer. Yet Dr. Grant says melanomas tend to be caused by UVA rays, which are highest during the morning hours, rather than the cancer-protective UVB rays, which increase at around 1 p.m. “You go out for a shorter time at midday and make your vitamin D, and then cover up,” he advises.
During the winter months or in more northern climates where sun exposure is generally lower, Dr. Grant advises taking vitamin D supplements to ensure that you’re getting enough.
To learn more about getting the optimum levels of vitamin D for your individual situation talk to your licensed healthcare provider.
Grant WB, Mohr SB. Ecological studies of ultraviolet B, vitamin D and cancer since 2000. Annals of Epidemiology, 2009.
Garland CF, Garland FC. Do sunlight and vitamin D reduce the likelihood of colon cancer? International Journal of Epidemiology. 1980;9:227-231.