EXECUTIVE SUMMARY

Breastfeeding for six months or longer cuts the risk of developing type 2 diabetes nearly in half for women throughout their childbearing years, according to results of a long-term observational study.
  • Women in the current analysis were ages 18-30 without diabetes during 1985-1986, the start of the study. Participants had one or more live births, reported their lactation duration, and were screened for diabetes up to seven times during 30 years of follow-up (1986-2016).
  • Findings from the investigation indicate that women who breastfed for six months or longer across all births had a 47% drop in their risk of developing type 2 diabetes in comparison to those women who did not breastfeed at all. Those women who breastfed for six months or less had a 25% decline in diabetes risk, figures suggest.

Breastfeeding for six months or longer cuts the risk of developing type 2 diabetes nearly in half for women throughout their childbearing years, according to results of a long-term observational study.1

To conduct the analysis, researchers focused on 1,238 women from the Coronary Artery Risk Development in Young Adults study, a national, multi-center investigation of cardiovascular disease risk factors. Women in the current analysis were ages 18-30 without diabetes during 1985-1986, the start of the study. Participants had one or more live births, reported their lactation duration, and were screened for diabetes up to seven times during 30 years of follow-up (1986-2016).

Findings from the investigation indicate that the women who breastfed their babies for six months or more across all births had a 47% decrease in risk of developing type 2 diabetes in comparison to women who did not breastfeed at all. Those women who breastfed for six months or less had a 25% decline in diabetes risk, figures suggest.1

“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 Erica Gunderson, PhD, MS, MPH, lead author and senior research scientist with the Kaiser Permanente Division of Research, in a statement accompanying the paper’s publication.

Although previous research on breastfeeding relied on self-reporting of diabetes onset and started to follow older women later in life, researchers involved in the current analysis followed women specifically during the period of childbearing and regularly screened them for diabetes before and after their pregnancies, Gunderson said. Scientists also accounted for pre-pregnancy metabolic risk, including obesity and fasting glucose and insulin, lifestyle behaviors, family history of diabetes, and perinatal outcomes, she noted.

What Could Lead to Benefits?

What are possible explanations for the lower risk of diabetes associated with lactation duration? Researchers in the current analysis note that lactating women have lower circulating glucose in both fasting and postabsorptive states, as well as lower insulin secretion, despite increased glucose production rates.2

Several plausible biological mechanisms could be responsible for breastfeeding’s protective effects, researchers note. These include the influence of hormones associated with lactation on the pancreatic cells that control blood insulin levels and thereby affect blood sugar. In the current study, the incidence of diabetes decreased in a graded manner as the duration of breastfeeding increased, regardless of race, gestational diabetes, lifestyle behaviors, body size, and other metabolic risk factors measured before pregnancy.1 This finding suggests that the underlying mechanism may be biological, Gunderson said.

Clinicians have known for a long time that breastfeeding provides many benefits to mothers and babies, but previous evidence indicated only weak effects on chronic disease in women, says Tracy Flanagan, MD, director of women’s health for Kaiser Permanente Northern California.

“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,” said Flanagan in the press statement. “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.”

What About Contraception?

According to the U.S. Selected Practice Recommendations for Contraceptive Use, postpartum women who are breastfeeding should not use combined hormonal contraceptives during the first three weeks after delivery (U.S. MEC 4 – should not be used) because of concerns about an increased risk for venous thromboembolism. During the fourth week postpartum, breastfeeding women generally should not use combined hormonal contraceptives (U.S. MEC 3 – use usually is not recommended unless other more appropriate methods are not available or acceptable) because of concerns about the potential effects on breastfeeding performance. New breastfeeding mothers with other risk factors for venous thromboembolism generally should not use combined hormonal contraceptives four to six weeks after delivery (U.S. MEC 3).3 Use of progestin-only methods (contraceptive implant, contraceptive shot, and progestin-only pills) prior to 21 days is classified as Category 2 (benefits outweigh theoretical or proven risks). Between 30 and 42 days postpartum and beyond, these methods are classified as Category 1 (no restrictions on use).4

Women who are breastfeeding exclusively (meaning, they are nursing at least every four hours during the day and every six hours at night, and they feed their infants only breast milk) can rely on the Lactational Amenorrhea Method of contraception. The Lactational Amenorrhea Method is the proactive application of exclusive breastfeeding during lactational amenorrhea for the first six months after delivery. If used perfectly, two out of 100 people who use breastfeeding as birth control get pregnant in the six months it can be used after a baby is born.5

REFERENCES

  1. Gunderson EP, Lewis CE, Lin Y, et al. Lactation duration and progression to diabetes in women across the childbearing years. The 30-Year CARDIA Study. JAMA Intern Med 2018; doi:10.1001/jamainternmed.2017.7978.
  2. Tigas S, Sunehag A, Haymond MW. Metabolic adaptation to feeding and fasting during lactation in humans.
    J Clin Endocrinol Metab 2002;87:302-307.
  3. Curtis KM, Jatlaoui TC, Tepper NK, et al. U.S. selected practice recommendations for contraceptive use, 2016. MMWR Recomm Rep 2016; 65(RR-4):1-66.
  4. Curtis KM, Tepper NK, Jatlaoui TC, et al. U.S. medical eligibility criteria for contraceptive use, 2016. MMWR Recomm Rep 2016;65:1-103.
  5. Hatcher RA, Trussell J, Nelson AL, et al. Contraceptive Technology: 20th revised edition. New York: Ardent Media; 2011.