Research found a link between the risk of developing breast cancer and average exposures to sunlight based on latitude (the further from the equator, the weaker the sun, the lower the body’s vitamin D production), the higher the incidence of breast cancer).

Whilst accepting that the 'Breast Cancer-Sunlight' hypothesis was supported by internal US cancer statistics (there was less breast cancer in sunny South-west US than in cloudy North-east US), Dr. Michael Thun, head of epidemiology research at the American Cancer Society, said that the study is too general. For instance, there are dietary sources of vitamin D, particularly fish, a factor ignored by the hypothesis. In the winter months at least, people living in the northern parts of the US, where more fish is eaten, have higher blood levels of vitamin D.