Grand Rounds

The 30-Year CARDIA Study: Does Breast Feeding Reduce the Risk for Diabetes?

BACKGROUND AND PURPOSE:

Longer length of lactation has been weakly linked to lower diabetes incidence in older women, solely through self-reported cases
- These studies are subject to recall bias and do not provide actual biochemical evidence of diabetes
No studies considered gestational diabetes (GDM), which is a major risk factor for type 2 diabetes in young women
Gunderson et al. (JAMA Intern. Med., 2018) evaluated the association between lactation and progression to diabetes in older women

Multicenter, community-based 30-year prospective cohort study
Subjects were derived from the Coronary Artery Risk Development in Young Adults (CARDIA) study
Current study was designed to evaluate progression to diabetes among young black and white women through multiple assessments of glucose tolerance and other risk factors through prepregnancy to the postweaning years
Participants
- Aged between 18 and 30 years at baseline
- Gave birth ≥1 times following baseline
- Reported lactation duration
- Underwent screening for diabetes up to 7 times during 30 years after baseline
Lactation duration categories
- None
- >0 to 6 months
- >6 to <12 months
- ≥12 months
Primary outcome
- Diabetes incidence rates per 1000 person-years and adjusted relative hazard ratio (RH)
Proportional hazards regression models were adjusted for confounding variables such as biochemical and reproductive risk factors

1,238 women were included in analyses
- mean [SD] age was 24.2 [3.7] years
Overall diabetes incidence rate of 6.6 cases per 1000 person-years (95% CI, 5.6-7.6)
Rates were significantly different when taking in to consideration GDM (P for difference < .001)
- With GDM: 18.0 (95% CI, 13.3-22.8)
- Without GDM: 5.1 (95% CI, 4.2-6.0)
Lactation duration was inversely related to diabetes incidence with the following RH values compared to 0 days lactation (Pfor trend = .01)
- 0.75 for > 0 to 6 months (95% CI, 0.51-1.09)
- 0.52 for > 6 months to < 12 months (95% CI, 0.31-0.87)
- 0.53 (0.29-0.98) for ≥12 months (0.29-0.98)
There was no evidence of effect modification by race, GD, or parity

This study demonstrated a strong, graded inverse association between lactation duration and diabetes incidence
The authors state that this study provides evidence that lactation may lower risk of diabetes and lead to further research into glucose intolerance

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