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Background: Previous studies suggest that over-nutrition in early infancy may programme long-term susceptibility to insulin resistance.
Objective: To assess the association of breast milk and quantity of infant formula and cows' milk intake during infancy with insulin resistance measures in early adulthood.
Design: Long-term follow-up of the Barry Caerphilly Growth cohort, into which mothers and their offspring had originally been randomly assigned, between 1972-1974, to receive milk supplementation or not. Participants were the offspring, aged 23-27 years at follow-up (n = 679). Breastfeeding and formula/cows' milk intake was recorded prospectively by nurses. The main outcomes were insulin sensitivity (ISI0) and insulin secretion (CIR30).
Results: 573 (84%) individuals had valid glucose and insulin results and complete covariate information. There was little evidence of associations of breastfeeding versus any formula/cows' milk feeding or of increasing quartiles of formula/cows' milk consumption during infancy (<3 months) with any outcome measure in young adulthood. In fully adjusted models, the differences in outcomes between breastfeeding versus formula/cows' milk feeding at 3 months were: fasting glucose (-0.07 mmol/l; 95% CI: -0.19, 0.05); fasting insulin (8.0%; -8.7, 27.6); ISI0 (-6.1%; -11.3, 12.1) and CIR30 (3.8%; -19.0, 32.8). There was also little evidence that increasing intakes of formula/cows' milk at 3 months were associated with fasting glucose (increase per quartile of formula/cows' milk intake = 0.00 mmol/l; -0.03, 0.03); fasting insulin (0.8%; -3.2, 5.1); ISI (0) (-0.9%; -5.1, 3.5) and CIR30 (-2.6%; -8.4, 3.6).
Conclusions: We found no evidence that increasing consumption of formula/cows' milk in early infancy was associated with insulin resistance in young adulthood.