A more recent study in the Journal of Epidemiology, found that exercise results in greater melatonin production during the following night, whilst the effect was greatest when exercise was taken later in the day. This could be the mechanism, which explains the anti-cancer value of physical activity.
Breast cancer is the worst fear for most women and it is widely evident that the disease is on the increase. The increased incidence of this diagnosis is most noticeable in western women. There have been a number of differing estimates of how rapid the increase has been in the western world. More in the main article.