Lactation Duration Linked to Diabetes Incidence

Erica P. Gunderson, PhD, MPH, MS

There now exists longitudinal biochemical evidence showing that lactation duration is impartially linked to the incidence of diabetes, according to new data.

CARDIA, a 30-year observational study led by Erica P. Gunderson, PhD, MPH, MS, an epidemiologist and senior research scientist from Kaiser Permanente Northern California, in Oakland, has shown that an increased duration of lactation was associated with a 25% to 47% relative reduction in diabetes incidence.

This reduction was observed even after pre-pregnancy biochemical measures, clinical and demographic risk factors, the presence of gestational diabetes, lifestyle, and weight gain were accounted for—factors unaddressed by previous studies.

"We have only just begun to characterize the lasting biological effects of lactation on women’s future cardiometabolic health," Gunderson told MD Magazine. "Research studies are needed to elucidate the mechanisms that could underlie the association between lactation and lower diabetes risk. This is unlikely to be due to obesity because 30-year weight gain did not weaken the association of breastfeeding with diabetes risk in our study."

The study analysis included 1238 women (615 black, 623 white) without diabetes before the time of pregnancy, who delivered 2302 infants post-baseline. Follow-up was done at years 7, 10, 15, 20, 25, and 30, with lactation duration reported at year 7 for all previous births (subsequent births were reported at later follow-up).

Women were assigned to 4 different categories of lactation duration: none (n = 322; 26.0%), >0 to 6 months (n = 418; 33.8%), >6 to <12 months (n = 268; 21.6%), and ≥12 months (n = 230; 18.6%).

Those with longer lactation duration showed a lower rate of diabetes (P = .02 for trend). Those in the ≥12 months group reported 10 cases of diabetes (2.7 incidence rate, 3753 person-years; 95% CI, 1.0—4.3). Meanwhile, the >6 to <12 months group reported 18 cases (3.4 incidence rate, 5367 person-years; 95% CI, 1.8–4.9), and both the >0 to 6 months group (5.5 incidence rate, 8866 person-years; 95% CI, 4.0–7.1) and the none group (7.5 incidence rate, 6506 person-years; 95% CI, 5.4–9.6) reported 49 cases.

All told, 86% of diabetes cases occurred from 15 to 30 years post-baseline, while 93% of post-baseline births occurred within 15 years post-baseline.

"The strong relative reduction in the risk of type 2 diabetes for women may provide greater impetus for physicians and health care systems to provide increased education and staffing for lactation support to pregnant women at greatest risk for future diabetes, and those who may have greater difficulty breastfeeding," Gunderson said. "Specifically, obese women often require greater lactation support, those with limited social support, and women with complications and medical conditions without contraindications to breastfeeding."

Gestational diabetes (GD) was reported by 155 (12.5%) women post-baseline (mean follow-up, 24.7 years [SD, 6.6]). Women with GD reported a higher incidence rate of diabetes per 1000 person-years (18.0; 95% CI, 13.3—22.8) compared to those without GD (51.; 95% CI, 4.2–6.0).

Diabetes was reported in 182 cases, at a rate of 6.6 cases per 1000 person-years (95% CI, 5.6—7.6). Black women reported 132 cases (73.0%) in 13,369 person-years for an incidence rate of 9.9 cases per 1000 person-years (95% CI, 8.2–11.6), while white women reported 50 cases (27.0%) in 14,229 person-years for an incidence rate of 3.5 cases per 1000 person-years (95% CI, 2.5–4.5; P <.001).

Recommendations from the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists point to a 1-year breastfeeding period, although data from the 2 institutions indicate that 70% of women in high- or middle-income countries do not meet that duration. In the US, only 55% of mothers reach a 6-month duration, with that number dropping to 33% by the 1-year mark, according to the CDC.

"Women face many barriers to breastfeeding in the modern society," Gunderson said. "Social policies, such as extended paid maternity, may potentially enable more women to breastfeed their children beyond 1 to 2 months. If longer breastfeeding lowers diabetes risk, then it could potentially reduce health care costs. Social policies that support women breastfeeding longer could be cost-effective."

The study, “Lactation Duration and Progression to Diabetes in Women Across the Childbearing Years,” was published in JAMA Internal Medicine.

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