30-year study shows effects of breastfeeding on diabetes incidence in women of child-bearing age.
Insulin resistance is common in pregnancy, leading to hyperglycemia and an increase in insulin secretion. During lactation, insulin levels are decreased due to reduced plasma glucose levels. Milk production has been linked to decreased activity for pancreatic beta-cells, preserving their function. Previous studies, based on self-reported diabetes from post-reproductive women, have shown the association between post-weaning and better metabolic profiles without weight loss differential. These studies have reported weak reductions in diabetes risk, 3%-15% with one year of lactation or 20% with one and a half years or more. Longitudinal studies lack the use of biochemical assessments. These assessments could provide a stronger association between lactation duration and diabetes progression. Evaluating gestational diabetes status could also give a better yield due to its strong correlation to the development of type 2 diabetes. One study showed that an increase in intensity and duration of lactation in women with gestational diabetes had a 34%-57% reduction of diabetes progression.2 This is the only study that accounts for reverse causation and confounding, which is a limitation in most studies. To break down these limitations, the following study focused on strengthening the protective association between breastfeeding and diabetes risk.
A 30-year prospective cohort study was designed to evaluate the association between lactation duration and the progression of diabetes in women of child-bearing age. 1,238 women were evaluated from the Coronary Artery Risk Development in Young Adults (CARDIA) study. These women were black and white, ranged from 18-30 years of age, and did not have a diabetes diagnosis at baseline. Biochemical testing was conducted before and after pregnancy using the homeostasis model assessment (HOMA-IR) and the National Cholesterol Education Program Adult Treatment Pane lII (NCEP-ATP III). Pre-pregnancy cardiovascular and metabolic status was recorded as well as the development of gestational diabetes and associated lifestyle. Testing was conducted up to seven times in the childbearing timeframe from pre-pregnancy to post-weaning. The primary outcome that was assessed was the reported lactation duration and if diabetes was developed during this 30-year study. This was measured using time-dependent lactation duration categories: None, >0-6 months, >6-<12 months, and ³ 12 months. Adjusted relative hazards was used to measure diabetes incidence while proportional hazards were used to measure biochemical, demographic, and reproductive risk factors.
Lactation was reported as 26% of women did not breastfeed, 33.8% breastfed up to six months, 21.6% breastfed for more than six months but less than a year, and 21.6% breastfed for 12 months or more. There were 182 overall incidences of diabetes with a higher rate reported in black women (9.9; 95% CI, 8.2-11.6) than white women (3.5; 2.5-4.5); (P<0.001). These women also had other confounding conditions, including a higher BMI, fasting glucose and triglycerides, lower physical activity and poor diet habits. Gestational diabetes was reported for 155 women (12.5%) resulting in a higher prevalence of diabetes in comparison to those without gestation diabetes (18; 13.3-22.8) vs. (5.1; 4.2-6.0) (P<0.001). Lactation duration proved to be inversely related with diabetes incidence. The lowest incidence report for lactation was a duration of more than 12 months 47% (P=0.02). Protective association between lactation duration and diabetes risk did not differ by race. Women who did not breastfeed tended to be younger black women with less education and a higher prevalence of metabolic syndrome. When assessing 12 months or more of lactation, non-lactating women had an increased risk of incident diabetes 2.08% higher than women with a history of gestational diabetes, and 0.48% higher than women without a history of gestational diabetes.
In conclusion, duration of lactation shows an independent relationship to lower incidence of diabetes, even when other risk factors are considered. Lactation results in lower circulating glucose levels, resulting in lower levels of insulin secretion. Prolactin stimulated milk production has also been linked to decreased activity for pancreatic beta-cells, preserving their function. It is also important to note the relationship between pre-pregnancy obesity, gestational diabetes, and their effect on delayed lactation. Although these findings do correlate with one another, they do not refute the protective association between lactation and the reduced risk of diabetes incidence. Strengths of this study were generalizability, longitudinal cohort analyzes, and controlling risk factors and observation window to minimize reverse causation. Some limitations include lack of randomization, timing of assessments, self-reporting, and inability to assess absolute lactation duration.
- Racial discrepancies in breastfeeding affect both the mother and child.
- Breastfeeding offers many benefits, including reducing the risk of diabetes in women.
- Breastfeeding may stop the progression from gestational diabetes to type 2 diabetes.
Gunderson, Erica P., et al. “Lactation Duration and Progression to Diabetes in Women Across the Childbearing Years.” JAMA Internal Medicine, 16 Jan. 2018, pp. 1–10., doi:10.1001/jamainternmed.2017.7978.
Gunderson, Erica P., et al. “Lactation and Progression to Type 2 Diabetes Mellitus After Gestational Diabetes Mellitus.” Annals of Internal Medicine, vol. 163, no. 12, 15 Dec. 2015, pp. 889–898., doi:10.7326/m15-0807.
Adrianna Jackson, Doctor of Pharmacy Candidate: Class of 2018; LECOM College of Pharmacy