Recreational sun exposure could help prevent a type of blood cancer involving the lymph nodes called non-Hodgkin’s lymphoma (NHL), according to pooled data from 10 studies.

“These results … could be taken to suggest that if sun exposure does protect against NHL it is an intermittent pattern of sun exposure that is the most protective,” Dr. Anne Kricker of the University of Sydney in New South Wales, Australia and colleagues note in the International Journal of Cancer.

Sun exposure could exert its anti-cancer effects by boosting vitamin D production in the skin, according to the researchers.

Some investigators have proposed that sun exposure increases the risk of NHL, given that people with skin cancer have a higher risk of the disease and that rates of melanoma have risen in tandem with NHL.

However, four studies conducted between 2004 and 2007 that directly investigated the relationship found sun exposure appeared to protect against NHL; a fifth study, in women only, showed an increased likelihood of NHL with sun exposure.

To systematically evaluate NHL risk and sun exposure, Kricker and colleagues looked at these five studies and an additional five from an international lymphoma study group. The studies included a total of 8,243 people with NHL and 9,697 people without the disease.

Recreational sun exposure between the ages of 18 and 40, as well as in the 10 years before a person was diagnosed with NHL, reduced the risk of the disease, the researchers found. They defined recreational sun exposure as the number of hours spent in the sun on non-working days.

There was no association between work-related sun exposure and NHL risk. Total sun exposure was linked to reduced risk, but the relationship wasn’t statistically significant.

Sunlight exposure causes the skin to produce vitamin D, which might help explain how sunlight could be protective against NHL, Kricker and colleagues suggest.

However, other factors could account for the relationship, they note, such as exercise, given that people with more recreational sun exposure would likely be more physically active.

Studies comparing the amount of vitamin D people have in their blood and their NHL risk will likely “provide a more certain answer.”

— From Reuters, The Vancouver Sun and Canada.com