Early life factors and type 2 diabetes in south India: Do the associations change with age?

Background: Studies since the early 1990s have shown that birth size can be a predictor of the development of Type 2 diabetes mellitus (T2DM). In the present study, we evaluated changes in the strength of associations between T2DM and birth size and maternal weight with age.

Methods: In 1993-1994 (t₀), 509 men and women (mean age 46 years) who had been born in Holdsworth Memorial Hospital were screened for diabetes, with increased diabetes risk identified in those who were shorter at birth and those born to heavier mothers. Ten years later (t₁₀), the screening was repeated in 266 subjects who were non-diabetic at t₀ (70% of survivors).

Results:   At t₁₀, 56 new cases of diabetes were found. The incidence of diabetes decreased with increasing birth length (odds ratio (OR) = 0.90, 95% confidence interval (CI) 0.84-0.97/cm birth length; P = 0.006) after adjustment for sex, age, socioeconomic status, family history, and current body mass index. Overall, there were no significant differences in OR for the association between birth length and diabetes at t₀ compared with t₁₀, but limiting analysis to subjects with normal glucose tolerance at t₀ resulted in a stronger association at t₁₀ (OR = 0.71, 95% CI 0.58-0.87) than at t₀ (OR = 0.95, 95% CI 0.86-1.05; P = 0.015 for the difference). There was a positive correlation between maternal weight and incident disease at t₀ (OR = 1.08, 95% CI 1.03-1.14; P = 0.001), but not at t₁₀ (OR = 0.98/kg, 95% CI 0.92-1.05; P = 0.6; P = 0.02 for the difference).

Conclusions:   Short birth length remains a risk factor for diabetes. Changes in the effects of birth length and maternal weight on diabetes risk with age may indicate different causal pathways. These findings require replication in studies with more accurate dating of the onset of diabetes.