Abstract
BACKGROUND: Understanding how bone (BM), lean (LM) and fat mass (FM) develop through childhood, puberty and adolescence is vital since it holds key information regarding current and future health. Our study aimed to determine how BM, LM and FM track from prepuberty to early adulthood in girls and what factors are associated with intra- and inter-individual variation in these three tissues. METHODS: The study was a 7-year longitudinal cohort study. BM, LM and FM measured using dual-energy X-ray absorptiometry, self-reported dietary information, leisure time physical activity (LTPA) and other factors were assessed one to eight times in 396 girls aged 10 to 13 years (baseline), and in 255 mothers once. RESULTS: The location of a girl's BM, LM and FM in the lower, middle or upper part of the sample distribution was established before puberty and tracked in its percentile of origin over 7 years (r = 0.72 for BM, r = 0.61 for LM, and r = 0.65 for FM all p < 0.001 first vs. last measurements' ranking). Seventy-three percent of those in the lowest quartile for BM and 69% for LM, and 79% of those in the highest quartile for FM at baseline remained in their quartile at 7-year follow-up. Heritability was estimated to contribute 69% of the total variance of the BM, 50% of the LM, and 57% of the FM. Besides body size, diet index (explaining 9% of variance), breast feeding duration (6%) and mother's BM (9%) predicted high BM. Diet index and high LTPA predicted high LM (24% and 14%, respectively), and low FM (25% and 12%, respectively), and low level of parental education predicted high FM (4%). CONCLUSION: Individual levels of BM, LM and FM are established before puberty and track in a trait-specific manner until early adulthood. Girls who are prone to develop low BM and LM and high FM in adulthood can be identified in prepuberty. The developments of three components of body composition are inter-related during growth. BM was the most heritable trait while LM the most environmentally modifiable. Diet and physical activity played an important role in increasing LM and preventing the accumulation of excessive FM.