Do ethnic differences in cord blood leptin levels differ by birthweight category? Findings from the Born in Bradford cohort study

BACKGROUND: There is evidence that South Asian individuals have higher fat mass for a given weight than Europeans. One study reported that the greater fatness for a given birthweight may increase with increasing birth weight, suggesting that any attempt to increase mean birth weight in South Asians would markedly increase their fatness. OBJECTIVE: Our objective was to examine whether differences in cord leptin values between White British and Pakistani infants vary by birth weight category. METHOD: We examined the difference in cord leptin levels between 659 White British and 823 Pakistani infants recruited to the Born in Bradford cohort study, by clinical categories and thirds of the birth weight distribution. RESULTS: Pakistani infants had a lower mean birthweight but higher cord leptin levels than White British infants [ratio of geometric mean(RGM) of cord leptin adjusted for birth weight = 1.36 (95% CI 1.26,1.46)]. Birthweight was positively associated with cord leptin levels in both groups, with no evidence that the regression lines in the two groups diverged from each other with increasing birthweight.The relative ethnic difference in cord leptin was similar in low (<2500 g), normal and high (>/=4000 g) birthweight infants(P-value for interaction = 0.91). It was also similar across thirds of the birthweight distribution [RGM (95% CI) in lowest, mid and highest thirds were 1.37 (1.20, 1.57), 1.36 (1.20, 1.54) and 1.31 (1.16, 1.52), respectively, P-interaction = 0.51]. CONCLUSIONS: We found marked differences in cord leptin levels between Pakistani and White British infants but no evidence that this difference increases with increasing birthweight.