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. 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. 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 (a parts per thousand currency sign3,180 g), intermediate (3,181-3,620 g), and high (a parts per thousand yen3,621 g) birth weight. 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. 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.