CARDIA Study: Lactation Duration Inversely Associated with Diabetes Progression in Women across the Childbearing Years

Background

Studies have demonstrated a weak association between lactation duration and reduction in the risk of incident diabetes (3%-15% lower incidence per year of lactation) in middle-aged to older women. With the lack of biochemical evidence to support this association, the risk estimates appear to be biased due to various confounding factors including gestational diabetes (GD), perinatal outcomes, and differences in lactation duration across the childbearing years.

Aim

The CARDIA (Coronary Artery Risk Development in Young Adults) study assessed the association between lactation and progression to diabetes using biochemical testing both before and after pregnancy

Study Participant Profile

• Young black (n=615) and white (n=623) women (age; 18 to 30 years) without diabetes at baseline with 1 or more live births after baseline and reporting lactation duration (n=1238)
• Participants were categorized as per the time-dependent lactation duration as follows:
  • None (n=322, 26%)
  • More than 0 to 6 months (n=418, 33.8%)
  • More than 6 months-to less than 12 months (n=268, 21.6%)
  • 12 months or more (n=230, 18.6%)

Screening/Follow-up

• Study participants were screened for diabetes up to 7 times during 30 years after baseline

Method

Study Design

• Multicenter, community-based 30-year prospective cohort study

Outcomes

• Diabetes incidence rates per 1000 person-years
• Relative hazards (RH) of diabetes, adjusted for biochemical, sociodemographic, and reproductive risk factors and other factors such as family history of diabetes, lifestyle, and weight change during follow-up.

Results

• One hundred and eight two incident diabetes cases were reported during 27598 person-years. This corresponded to an overall incidence rate of 6.6 cases per 1000 person-years.
• Incidence rate (/1000 person-years) of diabetes was higher in women with GD vs. those without GD (18.0 vs. 5.1, P for difference < 0.001).
• Lactation duration had a strong, graded inverse association with diabetes incidence (P for trend = 0.01) (Table 1)

• No lactation was associated with a per year excess risk of incident diabetes of 2.08% in women with GD history and 0.48% in women without GD history as compared to lactation for a duration of 12 or more months.

Conclusions

• Lactation duration was independently associated with lower incidence of diabetes.
• Strategies to increase and improve breastfeeding practices are warranted to mitigate the risk of chronic diseases such as diabetes in women.

JAMA Intern Med. Jan 16, 2018 (Published online); doi:10.1001/jamainternmed.2017.7978