Bone Abstracts

We have previously reported sex-specific effects of prepubertal calcium supplementation on the timing of adolescent growth,¹ as well as sex-specific effects of maternal calcium supplementation on offspring childhood growth,^2,3 in a rural Gambian population with habitually low calcium intake (~300 mg daily). In this study, we aim to investigate longer-term effects of maternal calcium supplementation on adolescent growth in same cohort. We recruited children (230 female, 217 male) born following a randomised, placebo-controlled trial of calcium supplementation during pregnancy (1500 mg daily from gestational week 20 until delivery, ISRCTN96502494). Height and weight were measured on three occasions, at mean(S.D.) ages 9.2(0.9), 13.8(1.2) and 16.3(1.3) years. Mixed effects models were used to determine the effects of maternal calcium supplementation on offspring growth trajectories of height, weight and BMI, on an intention-to-treat basis, separately among boys and girls. The outcomes were log-transformed to allow interpretation of the coefficients as percentage differences, fixed effects were fitted as natural cubic splines, and random effects were included to model between-subject variation in the intercepts and slopes. Boys and girls were then pooled to test for a sex-supplement interaction. Girls whose mothers had received the calcium supplement during pregnancy were shorter and lighter than those whose mothers received placebo (mean(95%CI) difference in height: −1.1(−2.1,−0.2)%; weight: −3.4(−6.8,−0.0)%). There were no significant supplement-age interactions, indicating that the difference was consistent across the age range studied. There was no difference in BMI (−1.3(−3.6,+1.0)%) among girls, and there were no differences among boys (height: +0.4(−0.7,+1.4)%; weight: +1.6(−1.7, +4.8)%; BMI: +1.0(−1.1,+3.1)%). The pooled analysis identified a significant sex-supplement interaction for weight only (height: +1.3(−0.2,+2.7)%; weight: +4.9(+0.2, +9.6)%; BMI: +2.2(−0.9,+5.4)%). Maternal calcium supplementation was associated with reduced height and weight among girls, but not among boys, with a significant sex-supplement interaction effect on weight. Despite low habitual calcium intake in this population, there was no evidence that maternal supplementation promoted offspring growth. Instead, these data suggest that calcium supplementation may have reduced growth among girls. It remains to be seen whether these differences are transient, e.g. as a result of differences in the timing of growth, or will be sustained into adulthood.

Funding: UK Medical Research Council and Department for International Development under the MRC/DFID Concordat (programmes U105960371 and U123261351); Sackler Institute for Nutrition Science, New York Academy of Sciences.

Disclosure: The authors declared no competing interests.

References:
(1) Prentice et al. AJCN 2012 96 1042–50.
(2) Ward et al. JBMR 2015 30 (S1) OP1096.
(3) Ward et al. OI 2016 27 (S1) P585.