Longer breastfeeding duration tied to reduced diabetes risk
Women who breastfed their infants for a longer duration appeared to have a lower risk of diabetes compared with women who did not breastfeed, according to an observational study spanning three decades.
“We found a very strong association between breastfeeding duration and lower risk of developing diabetes, even after accounting for all possible confounding risk factors,” said study lead author Dr Erica P. Gunderson, a senior research scientist with the Kaiser Permanente Division of Research, Oakland, California, US.
The cohort comprised 1,238 women aged 18–30 years (mean age 24.2 years) from the multicentre, prospective US-based CARDIA* study who did not have diabetes at recruitment (1985–1986) but had ≥1 live births during follow up. The participants provided information on lactation duration and were screened for diabetes up to seven times over the 30-year follow-up period.
One hundred and fifty-five women reported gestational diabetes over the mean 24.7-year follow-up period. There were 182 cases of diabetes equivalent to an incidence rate of 6.6 cases per 1,000 person-years; the incidence rate of diabetes was higher among women previously diagnosed with gestational diabetes (18.0 per 1,000 person-years vs 5.1 per 1,000 person-years for women without prior gestational diabetes; p<0.001).
Women with a longer duration of breastfeeding across all births had a lower risk of diabetes compared with women who did not breastfeed, with a 25 percent decrease among women who breastfed for up to 6 months (adjusted** relative hazard [adjRH], 0.75, 95 percent confidence interval [CI], 0.51–1.09) to a 47 percent decrease among women who breastfed for ≥12 months (adjHR, 0.53, 95 percent CI, 0.29–0.98; ptrend=0.01). There was no effect modification exerted by race, parity, baseline body mass index, and gestational diabetes status. [JAMA Intern Med 2018;doi;10.1001/jamainternmed.2017.7978]
Compared with ≥12 months of lactation, no lactation was associated with an excess diabetes risk of 2.08 percent per year in women with a history of gestational diabetes, and a 0.48 percent per year increase among women without a history of gestational diabetes.
“The incidence of diabetes decreased in a graded manner as breastfeeding duration increased, regardless of race, gestational diabetes, lifestyle behaviours, body size, and other metabolic risk factors measured before pregnancy, implying the possibility that the underlying mechanism may be biological,” said Gunderson.
Among the potential mechanisms cited were the influence of lactogenic hormones as well as the beneficial effects of milk production processes on pancreatic β-cells.
“Unlike previous studies of breastfeeding, which relied on self-reporting of diabetes onset and began to follow older women later in life, we were able to follow women specifically during the childbearing period and screen them regularly for diabetes before and after pregnancies,” said Gunderson on the strengths of this study over previous ones.
However, the authors acknowledged that an absolute duration of lactation could not be ascertained owing to obtaining a maximum 6-month lactation duration per birth.
“We have known for a long time that breastfeeding has many benefits both for mothers and babies; however, previous evidence showed only weak effects on chronic disease in women,” said Dr Tracy Flanagan, director of women’s health for Kaiser Permanente Northern California, who was not involved in the study.
“Now we see much stronger protection from this new study showing that mothers who breastfeed for months after their delivery may be reducing their risk of developing type 2 diabetes by up to one half as they get older. This is yet another reason that doctors, nurses, and hospitals as well as policymakers should support women and their families to breastfeed as long as possible,” said Flanagan.