NEW YORK (Reuters Health) - In women, ultraviolet radiation exposure from time spent in the sun appears to boost the risk of non-Hodgkin's lymphoma -- a type of cancer involving the body's lymphatic system, according to a large "population-based" study.

It's been suggested that increasing exposure to ultraviolet radiation may be responsible, at least in part, for the observed increase in the incidence of non-Hodgkin's lymphoma.

To investigate, Dr. Yawei Zhang of Yale University, New Haven, Connecticut and colleagues examined data from a case-control study of women living in Connecticut. The study involved 601 women with confirmed non-Hodgkin's lymphoma and female controls who were also Connecticut residents.

A history of suntan was generally associated with an increased risk of lymphoma. In particular, compared to women who had never had a suntan, those who had had a suntan for less than 3 months per year for more than 60 years were at almost 3 times the risk.

However, there appeared to be no increased risk in women who reported having a suntan for 3 or more months per year. The researchers consider a lower suntan duration to have been indicative of irregular exposure. A regular suntan, they suggest, may have provided protective pigmentation that would reduce ultraviolet radiation absorption.

In addition, women with the greatest exposure to strong sunlight between 9 a.m. and 3 p.m. in the summer had a 70 percent increased risk compared to those with the lowest exposure.

The investigators think further studies are warranted "to investigate whether genetic susceptibility may modify the relation between sun exposure and risk of non-Hodgkin's lymphoma."