WHO has updated the longterm effects of breastfeeding
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Interpreting the results of the present meta-analyses jointly with those of the two randomized trials, our conclusions are outlined below.
Total cholesterol. There was no effect in the overall meta-analyses. In the 2007 review, there was a significant effect among adults, which is no longer present in the updated analyses. The UK trial of preterm infants showed a small protective effect (3), while the Belarus trial did not report on this outcome. We conclude that breastfeeding does not seem to protect against total cholesterol levels.
Blood pressure. The pooled estimate from the high-quality studies indicates a small reduction of less than 1 mmHg in systolic pressure among breastfed subjects, and no significant protection in terms of diastolic pressure. Residual confounding may be an important problem. The Belarus and UK preterm trials found no effect of breastfeeding (2,4). We conclude that the protective effect of breastfeeding, if any, is too small to be of public health significance.
Diabetes. There was substantial protection in the pooled analyses, with a 34% reduction, but few studies are available and their results were considerably heterogeneous. Only two high-quality studies were identified, with conflicting results (one showing an increase and another a reduction among breastfed subjects). The randomized trials did not present any results on these outcomes. Our conclusion is that further studies are needed on this outcome.
Overweight-obesity. In the pooled analyses of all studies, breastfeeding was associated with a 24% reduction in overweight and/or obesity, but the reduction was only 12% in the high-quality studies. Residual confounding may be still affecting these results, because protection is not evident in studies from low and middle-income countries where the social patterning of breastfeeding is not clear cut. The Belarus trial did not find an association (4). We conclude that breastfeeding may provide some protection against overweight or obesity, but residual confounding cannot be ruled out.
Intelligence tests. Breastfeeding was associated with an increase in 3.5 points in normalized test scores in the pooled analyses of all studies, and 2.2 points when only the high-quality studies are included. The two randomized trials also found significant effects (1,5). We conclude that there is strong evidence of a causal effect of breastfeeding on IQ, although the magnitude of this effect seems to be modest.