Sun Exposure May Reduce Malignant Lymphoma Risk

At last, some positive health effects of sitting in the sun! Physicians have found that recreational sun exposure is apparently associated with reduced risk for cancers of the lymph system, or malignant lymphomas, German researchers report in the International Journal of Cancer.

They also found that the association is stronger for some types of lymphoma than for others.

However, this must still be balanced against the strong association between sun exposure and skin cancers, including melanoma, a potentially lethal cancer that can spread and be hard to treat.

Reports investigating an association between ultraviolet (UV) light exposure and lymphoma risk have yielded conflicting results, the authors explain, probably because of difficulties in assessing exposure.

Dr. Thomas Weihkopf from Johannes-Gutenberg University, Mainz, and colleagues therefore examined the relationship between malignant lymphoma and lifetime exposure to UV in different settings, including outdoor leisure activities, vacations, sunbed use and occupational exposures.

The investigators recruited 710 patients with malignant lymphoma from six regions of Germany and matched them with individuals drawn from population registries.

The number of vacations spent in sunny climates was inversely associated with a diagnosis of lymphoma, the researchers report, especially for Hodgkin lymphoma and B-non-Hodgkin lymphoma. After accounting for other factors associated with lymphoma risk, the researchers found that individuals who spent more than 1,190 cumulative days in sunny locations had a 60-percent lower risk than those in sunny locations for 350 days or less.

Outdoor leisure and occupational activities had no statistically significant association with a lymphoma diagnosis, the results indicate. One exception was high UV exposure during outdoor leisure activities up to age 15 years, which was associated with an increased risk of lymphoma.

Frequent outdoor leisure activities were also significantly associated with an increased risk of T-non-Hodgkin lymphoma and follicular lymphoma.

There was a trend toward fewer lymphoma diagnoses among frequent sunbed users, the researchers note, and frequent sunbed or sunlamp use was negatively associated with B-non-Hodgkin lymphoma and diffuse large B-cell lymphoma.

When all potential lymphoma risk factors were considered in the analysis, the findings "point to a possible independent protection against malignant lymphoma from vacations at sunny places and from the use of sunbeds," the authors conclude.

"Possible explanations for this protective effect lie in the stimulation of vitamin D production or in the modulation of T-cell immunology" that are stimulated by UV exposure, they suggest.

SOURCE: International Journal of Cancer, June 1, 2007.