Women who gain weight between the age of 18 years and post-menopausal years may be twice as likely to develop breast cancer as those who do not. Zhiping Huang and his colleagues at the Harvard School of Public Health, Boston, USA, say that staying within 2-4 kg of one's weight at age 18 may reduce such risks. When the ovaries shut down after menopause, body fat is the main source of natural oestrogen. In such cases, weight gains severely affect women who are not supplemented with oestrogen pills. Non-hormone users who put on nearly 20 kg after age 18 double the risk of developing breast cancer. About 16 per cent of post-menopausal breast cancers are linked to weight gain.