Associations of birth weight and length, childhood size, and smoking with bone fractures during growth: evidence from a birth cohort study.

Little information exists on risk factors associated with bone fractures during childhood and adolescence. This 1972/1973-1990/1991 New Zealand study examined the influence of birth size, height and weight throughout growth, smoking, breastfeeding, and sports participation on the risk of fracture in participants of the Dunedin Multidisciplinary Health and Development Study. Information on height, weight, fracture status, and lifestyle was collected at birth and at ages 3, 5, 7, 9, 11, 13, 15, and 18 years from parents and/or participants. Study members sustained 229 (girls) and 393 (boys) fractures between birth and age 18 years. Fracture risk was elevated (per standard deviation unit increase) in relation to birth length (prepubertal fractures only) (risk ratio (RR) = 1.28, 95% confidence interval (CI): 1.04, 1.58), weight at age 3 years (RR = 1.14, 95% CI: 1.03, 1.27), weight from ages 5 to 18 years (RR = 1.15, 95% CI: 1.03, 1.28), height at age 3 years (RR = 1.13, 95% CI: 1.01, 1.26), and height from ages 5 to 18 years (RR = 1.13, 95% CI: 1.02, 1.24). Birth weight, maternal smoking, breastfeeding, and sports participation had no significant effect on fracture risk. However, for teenagers, personal daily smoking increased the risk of fracture (RR = 1.43, 95% CI: 1.05, 1.95). The authors concluded that tall and heavy children had an increased risk of fracture, as did adolescents who smoked regularly.