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Do breast fed babies have lower blood pressure as adults?

 

Clinical bottom line

Only small studies show that breast feeding reduces blood pressure in later life. Larger studies show no such association. This paper has a clear message: small studies showing positive results need to be treated very cautiously.


Background

Studies have suggested that breast feeding in infancy may protect against high blood pressure in later life. As most of these studies have been small, this paper performs a meta-analysis to examine whether breast feeding, compared with bottle feeding formula milk, is associated with lower blood pressure in adulthood.

Reference


CG Owen et al. Effect of breast feeding in infancy on blood pressure in later life: systematic review and meta-analysis. British Medical Journal 2003: 1-7.


Systematic review

The literature was searched using Embase, MEDLINE and Web of Science databases for studies showing the effects of feeding in infancy on blood pressure in later life.

Twenty-four studies were identified with 26 estimates of systolic blood pressure and 23 estimates of diastolic blood pressure. Twelve were case-control studies, eleven were cohort and one was a randomised controlled trial.

Results

With all studies in the analysis, mean systolic blood pressure was lower in breastfed participants than in bottle fed participants (-1.1 mmHg, 95% CI -1.8 to -0.4 mmHg).

Performing the analysis by study size, only small studies found systolic blood pressure to be lower in breastfed participants (shown in Table 1). No associations were found between diastolic blood pressure and type of feeding in infancy.

Table 1. Differences in systolic blood pressure between breastfed and bottle fed participants by study size.

Study size
Number of estimates of systolic blood pressure
Mean difference (95% CI)
<300 participants
13
-2.05 (-3.30 to -0.80)
300-1000 participants
9
-1.13 (-2.53 to 0.27)
>1000 participants
4
-0.16 (-0.60 to 0.28)

 

Comment

This meta-analysis has a powerful message about interpreting results from studies with small sample sizes. Small studies found an association, larger studies did not. Smaller studies finding significant associations are likely to get published, but it is difficult to draw reliable conclusions from them (as they are more likely to find significant results based on chance). The situation here with observational studies (larger effect size with small studies) is exactly the same as is found with clinical trials. Sensitivity analysis based on size makes sense in most meta-analysis.

With reference to this paper, mothers unable to breastfeed (but wanted to) need not feel guilty that they are adversely affecting their child's blood pressure in later life.