Birth weight is more important for peak bone mineral content than for bone density: the PEAK-25 study of 1,061 young adult women.

Lower birth weight has a negative association with adult BMC and body composition in young adult Swedish women.

INTRODUCTION: The aim of this study was to evaluate the influence of birth weight on peak bone mass and body composition in a cohort of 25-year-old women.

METHODS: One thousand sixty-one women participated in this cross-sectional population-based study using dual energy X-ray absorptiometry (DXA) to assess bone mineral content (BMC), bone mineral density (BMD), and body composition (total body (TB), femoral neck (FN), total hip (TH), lumbar spine L1-L4 (LS), and lean and fat mass). Birth weight data was available for 1,047 women and was categorized into tertiles of low (≤3,180 g), intermediate (3,181-3,620 g), and high (≥3,621 g) birth weight.

RESULTS: Significant correlations were observed between birth weight and TB-BMC (r = 0.159, p < 0.001), FN-BMC (r = 0.096, p < 0.001), TH-BMC (r = 0.102, p = 0.001), LS-BMC (r = 0.095, p = 0.002), and lean mass (r = 0.215, p < 0.001). No correlation was observed between birth weight and BMD. The estimated magnitude of effect was equivalent to a 0.3-0.5 SD difference in BMC for every 1 kg difference in birth weight (151 g (TB); 0.22 g (FN); 1.5 g (TH), 2.5 kg TB lean mass). The strongest correlations between birth weight and BMC occurred in women with lowest birth weights, although excluding women who weighed <2,500 g at birth, and the correlation remained significant although slightly weaker.

CONCLUSIONS: Women with lower birth weight have lower BMC and less lean and fat mass at the age of 25, independent of current body weight. Lower birth weight has a greater negative influence on bone mass than the positive influence of higher birth weight.