Sunlight reduces the chances of developing tumours in the lymphatic glands

A new study from Karolinska Institutet and Uppsala University shows that, contrary to previous belief, sunlight reduces the chances of developing tumours in the lymphatic glands (malignant lymphoma). The study is to be published in the next number of The Journal of the National Cancer Institute.

The number of new cases of lymphoma per year has tripled over the past 40 years, and the reasons are largely still a mystery. One hypothesis is that frequent exposure to the sun might increase the risk of developing this kind of cancer, especially the more common non-Hodgkin’s form, but also the Hodgkin’s type as well. However, a fresh study by research scientists at Karolinska Institutet and Uppsala University together with researchers from Denmark shows, on the contrary, that frequent exposure to ultraviolet rays, not only from the sun but also from sun lamps and solariums, seems to reduce the chances of developing Lymphoma, particularly non-Hodgkin’s, by some 30-40 per cent.

“We find a similar correlation if we analyse responses by country or by skin-type,” says Karin Ekström Smedby, postgraduate at KI’s Department of Medical Epidemiology and Biostatistics. “This reduces the risk of systematic error and increases the credibility of our study.”

The study was based on telephone interviews with more than 3,000 patients who were newly diagnosed as having malignant lymphoma, either non-Hodgkin’s or Hodgkin’s, between 1999 and 2002 in Sweden and Denmark, and just over 3,000 randomly chosen healthy members of the public. Participants were also asked about previous forms of diagnosed cancer.

It is already known that frequent exposure to the sun can increase the risk of skin cancer. If the results of this study can be replicated and complemented with additional data, Ms Ekström Smedby believes that advice about sunbathing might have to be amended.

“But we haven’t looked into the mechanisms behind the effect of sunlight on lymphoma,” she says. “More research is needed before we can give advice about the dangers and benefits of sunbathing in a wider perspective.”

Researchers will now continue with other studies to identify the possible biological mechanisms behind this relationship.