Minerva

Breast milk is better for babies than formula milk, but does it make them more intelligent? A meta-analysis concludes that breast feeding gives babies a three point advantage in IQ over bottle fed babies (American Journal of Clinical Nutrition 1999;70:433-4). The advantage is greatest in those born before term. Debate continues, however, over whether factors like social class and maternal education can ever be completely accounted for in studies of breast feeding, which can never be randomised trials.

The same arguments apply to emerging evidence that breast feeding reduces the risk of childhood leukaemia (Journal of the National Cancer Institute 1999;91:1765-72). A large case-control study of over 2000 children with leukaemia suggests that breast feeding reduces the risk of leukaemia by about 20%. The effect is strongest in children who were breast fed for more than six months. Well known immunological benefits of breast milk make these findings biologically plausible. Other investigators should try to confirm them.

Papers reporting odds ratios in double figures are unusual because medical research is rarely that conclusive. It's hard to argue, however, with an odds ratio of 74.6 describing the impact of smoking 40 cigarettes a day on young women's risk of heart attack (Heart 1999;82:581-3). The …