New evidence points to a strong link between raised progesterone levels and the eventual development of breast cancer.
Using data collected from several countries, researchers analysed progesterone levels in women aged 25-35 during the mid luteal phase of their cycles (from five to nine days preceding the next period). This phase is when progesterone levels are known to be at their highest.
They found that, during this phase, an increase in progesterone of more than 70 per cent coincided with a more than eightfold rise in the rate of breast cancer.
The authors also noted that a higher calorie intake often correlated with higher levels of progesterone. They concluded that an increase in physical activity and a decrease in caloric intake may help to keep levels of both progesterone and oestrogen in check (BMJ, 2001; 322: 586-7).