Does the duration of breast feeding matter?

Maybe—but not enough to counter current support for breast feeding

Any suggestion that breast feeding could confer long term disadvantage seems immediately counterintuitive. It is also controversial. A paper in this week's BMJ contains evidence to suggest, however, that extended breast feeding may lead to later adverse cardiovascular outcomes (p 643).1

In developing countries exclusive breast feeding is associated with reduced mortality and improved growth. In developed countries it also confers advantages: in addition to reducing childhood infections, breast feeding may also protect against later diseases such as insulin dependent diabetes mellitus, inflammatory bowel disease, coeliac disease, and lymphoma.2 More recently, breast milk consumption by preterm infants has been shown to be associated with lower blood pressure in early teens.3 The superiority of breast feeding is therefore unchallenged, but its optimal duration has not been adequately investigated, and breast feeding is currently recommended for “as long as is mutually desired.”2 Several challenging strands of evidence now point to the need to reappraise that view.

Over a decade ago epidemiological studies showed an association between disproportionate fetal growth resulting from fetal undernutrition and an increased incidence of an unfavourable constellation of adult cardiovascular disease, hypertension, glucose intolerance, and hyperlipidaemia.4 They also showed an increased risk of death from ischaemic heart disease in men who had been breast fed and not weaned at one year (standardised mortality ratio 97) compared with those who were weaned at one year (SMR 79) and those who had been breast and bottle …