Summary: Sunlight exposure during leisure activities and risk of prostate cancer in Montréal, Canada, 2005-2009
Jennifer Yu, Jérôme Lavoué, and Marie-Élise Parent
Prostate cancer is the leading cause of cancer in men in many developed countries, but no modifiable risk factors have been identified. This means that there are no known risk factors that lend themselves to disease prevention. One clue is that migrants have been shown to take on the prostate cancer risk of their host countries, implying that the environment might play a role. Sunlight exposure is just one type of environmental influence that has been investigated thus far.
Scientific evidence remains sparse – and conflicting – in terms of the role of sunlight exposure in prostate cancer. These researchers investigated adult leisure-time sunlight exposure and prostate cancer risk, in the largest such study to date that has taken into account individual sunlight-related behaviour, and found little proof of any association. Men who were never exposed to sunlight (about 2.8% of both cases and controls) showed slightly higher risk than those who were, but the numbers were not significant. These conclusions were the same for both non-aggressive and aggressive prostate cancer.
Information for this study was gleaned from in-person interviews with 1904 men with prostate cancer from the Montreal area, and 1962 men without the disease of about the same age. These interviews asked about the frequency, seasonality, and duration (in total years) of participation of leisure activity during adulthood. Duration in cumulative hours was assessed according to time typically spent doing each activity. The researchers then had to judge whether these activities were indoors or outdoors. Other questions were also asked that allowed the researchers to account for age, ancestry, family history of prostate cancer, prostate cancer screening, education, solar protection, body mass index and physical activity in their analyses. Few other studies have taken into account such an extensive range of possible factors that might skew the results, especially the use of solar protection. This investigation did not, however, take into account sunbathing or exposure while traveling to work or elsewhere. Also, while they did examine workplace exposure, it did not affect the findings.
Since the study was based in Montreal, Canada, the findings might not be comparable to areas with greater solar radiation intensity, nor in a population composed of those from different ancestries (this population was of primarily European descent). These variations would also align with the possibility that vitamin D is the means through which sunlight exerts a protective effect against cancer. If this is the case, studies would also need to consider clothing coverage, skin type, geographical location, weather conditions, and diet. In this study, each recreational sunlight event was considered to provide an equal dose of exposure. If not vitamin D, sunlight might affect cancer incidence through UV-induced nitric oxide.
Future studies of prostate cancer should use more precise individual assessment of sunlight exposure. If sunlight exposure is indeed shown to be linked to prostate cancer risk, the findings would have great significance for public health. Given the increasing numbers of new cases, and the lack of strong leads in the search for the causes of prostate cancer, efforts to identify risk factors based on strong study designs must be pursued.