Breastfed boys do better in school?
Breastfed baby boys may outperform their peers in reading, writing and arithmetic.
The research, which followed more than 1,000 children, found that 10-year-old boys who had been predominantly breastfed until at least the age of 6 months did somewhat better on a set of academic tests.
Compared with boys who'd been breastfed for less time, they scored an average of 10% higher in math and writing, 8% higher in spelling and 6% higher in reading.
However, no clear advantage was seen among breastfed girls.
The findings, reported in the journal Paediatrics, do not prove that breastfeeding itself boosted boys' academic achievement. Indeed, the most important predictor of the boys' performance was how much time parents spent reading with the child from an early age.
Nonetheless, even after accounting for such factors that could explain the link, including family income and mothers' education levels, the association between breastfeeding and boys' test performance remained.
The researchers say the results bolster what experts already recommend on breastfeeding.
"We know that breast milk, if the mother has a good diet, is the optimum and 'best' way of feeding a newborn baby - boys and girls - until at least 6 months and beyond," said lead researcher Wendy H. Oddy.
Breastfeeding is believed to lower infants' risk of diarrhoea, ear infections and sudden infant death syndrome (SIDS), and possibly to have longer term health benefits as well. Some studies have found that breastfed babies go on to have lower rates of asthma, obesity and diabetes.
Breast milk also contains essential fatty acids involved in brain development, noted Oddy.
In line with that, some studies have linked breastfeeding to higher childhood IQ and better school performance. But not all have found that link, and questions remain about whether the advantage comes from breast milk.
For their study, Oddy and her colleagues began following mothers during pregnancy, and then assessed their children periodically through the age of 10. They were able to collect information such as how often parents read to their kids, to try to account for other factors that could explain any link between breastfeeding and academic prowess.
With those influences taken into account, longer term breastfeeding was still linked to better test scores in math, reading, writing and spelling in boys.
According to Oddy, it is plausible that breastfeeding could affect academic performance differently in boys and girls.
There is evidence that boys are more vulnerable to "adversity" during critical periods of brain development than girls are. It's possible that the estrogens in breast milk have a protective effect on brain cells, benefit boys more than they do girls.
Another theory is that boys might gain more from the mother-child bonding that comes with breastfeeding.
Still, even if breastfeeding was responsible for the higher test scores in boys, the effects were modest.
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