Researchers from Sweden and Denmark have reported that ultraviolet (UV) exposure does not increase the incidence of malignant lymphomas, but instead is associated with a lower incidence of non-Hodgkin’s lymphoma (NHL). The details of this report appeared in the February 2, 2005 issue of the Journal of the National Cancer Institute .
The incidence of malignant lymphoma has been increasing over the past several decades in the US population. The reasons for this increase are unknown. In fact, the causes of most lymphomas are unknown, except for the relatively few that are associated with specific bacteria (Helicobacter pylori in gastric lymphoma), or viruses such as the Epstein-Barr virus (Burkitt’s lymphoma), HIV-related lymphomas, body cavity lymphomas (human herpes virus-8) or T-cell lymphoma (HTLV-1). However, none of these specific causes explains the increased incidence of lymphomas observed in recent years. There is speculation that exposure to chemicals, such as certain solvents, pesticides, herbicides, and water contaminated with nitrate, are responsible for the increased incidence of lymphomas. Another speculation is that the increased incidence of lymphomas is due to an increase in sun exposure.
Researchers carrying out the current study looked at sun exposure in 3,740 patients with non-Hodgkin’s lymphoma, Hodgkin’s lymphoma or chronic lymphocytic leukemia and 3,187 individuals without lymphoma. They found that different types of sun exposure were associated with a decreased incidence of NHL. The types of sun exposure associated with a 30-40% decrease in the incidence of NHL included high frequency of sun bathing, sun vacations and sunburns. They also reported a greater effect for increasing sun exposure. The decreased incidences of chronic lymphocytic leukemia and Hodgkin’s lymphoma were not statistically significant, but there was no indication that sun exposure increased the incidence of these two diseases. Paradoxically, they found an increased incidence of Hodgkin’s and NHL in patients who were diagnosed with basal cell cancer, squamous cell cancer or melanoma.
This study shows clearly that increasing sun exposure is not the cause of the increased incidence of malignant lymphomas in the general population. The authors also speculate that the correlation between skin cancers and increased number of lymphomas is not mediated by the sun exposure.
Reference: Ekstrom K, Hjalgrim H, Melbye M, et al. Ultraviolet Radiation Exposure and Risk of Malignant Lymphomas. Journal of the National Cancer Institute. 2005:97:199-209.
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