Sunshine Vitamin DThose long, dreary January days might do more than give you a case of the winter blues. New research finds that staying indoors too much might actually affect your risk of developing lung cancer. 

Although cigarette smoking is by far the biggest cause of lung cancer, accounting for more than 85 percent of cases according to the National Cancer Institute, a lack of vitamin D might play a significant role in most of the remaining cases, says Cedric F. Garland, DPH, professor in the Department of Family and Preventive Medicine at the University of California, San Diego.

Dr. Garland and his colleagues recently looked at lung cancer incidence rates for 111 countries using a global cancer database. After controlling for cigarette smoking, they found that lung cancer incidence was higher in northern latitudes, and exposure to the sun’s ultraviolet B (UVB) rays was associated with reduced rates of lung cancer in both men and women.

Cellular Glue

The majority of vitamin D in the body is produced when the skin is exposed to sunlight. Vitamin D affects cancer risk by regulating the secretion of a substance called e-cadherin, which is a sort of glue that causes cells to stick together, says Dr. Garland. “When cells are stuck tightly to one another, they inhibit one another’s growth. This is called contact inhibition,” he says.

Without adequate vitamin D, the cells start to separate, giving them room to reproduce. As they reproduce, the cells have to compete for limited resources. “Some cells divide faster than others. Those that divide fastest will eventually predominate as a crowded, disorganized mass of rapidly-dividing cells competing for nutrients and oxygen,” Dr. Garland says. “The most aggressive cells overwhelm the more normal cells. The mass develops a blood supply and becomes a malignancy [cancer].”

This isn’t the first study to find a connection between vitamin D and cancer. Previous research by Dr. Garland and his colleagues linked adequate vitamin D to reduced rates of colon, breast, kidney, ovarian, and endometrial cancers. Research also has found that vitamin D intake can improve survival rates in people who already have lung cancer.

Get Outside

The best way to ensure that you’re getting enough vitamin D is to get outside in the sun for 10-15 minutes every day between the peak sun hours of 11 a.m. and 1 p.m., says Dr. Garland (African American people should stay out twice as long, because they only make one-fifth the amount of vitamin D as Caucasians).

Sounds easy, but there are a couple of catches: First, at least 40% of your body must be exposed to sunlight in order for it to be absorbed appropriately. That means you’d have to wear shorts and a t-shirt (or no shirt for men), which is difficult to do if it’s 25 degrees in the middle of January.

You also can’t wear sunscreen, because it will block your skin’s ability to absorb sunlight. Considering that prolonged sun exposure can lead to skin cancer, Dr. Garland recommends always wearing a wide- brimmed hat when you’re outside, and putting on sunscreen and protective clothing as soon as you’ve gotten your 15 minutes of unprotected sun exposure. “The sunscreen should have a protection factor of at least 15 in the ultraviolet A (UVA) part of the sun’s spectrum, as well as the usual protection in the ultraviolet B spectrum,” says Dr. Garland. “UVA is about 97% of solar ultraviolet, and blocking it after the short time spent making vitamin D daily is a key to preventing skin cancer. Clothing blocks UVA better than sunscreen.”

If you live in a northern climate, or you have a history of skin cancer or sensitivity to the sun that would preclude you from getting outside, ask your doctor about taking a vitamin D supplement. Although research still needs to determine the optimal dose, 2,000 IU daily should give you what you need. Also add food sources of vitamin D, such as milk and yogurt, to your diet.

The best advice when it comes to lung cancer is to quit smoking. “But for non-smokers, vitamin D is the best thing they have. There isn’t any other practical way to reduce risk of lung cancer in nonsmokers,” Dr. Garland says.

Before embarking on any supplement, dietary, or solar health program you should consult with your professional clinician.

Mohr SB, Garland CF, Gorham ED, Grant WB, Garland FC. Could ultraviolet B irradiance and vitamin D be associated with lower incidence rates of lung cancer? J Epidemiol Community Health, 2008;62:69-74.

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