Vitamin d, calcium, and dairy intakes and stress fractures among female adolescents.

OBJECTIVE To identify whether calcium, vitamin D, and/or dairy intakes are prospectively associated with stress fracture risk among female adolescents. DESIGN Prospective cohort study. SETTING Adolescent girls living throughout the United States. PARTICIPANTS A total of 6712 girls aged 9 to 15 years at baseline in the Growing Up Today Study, an ongoing prospective cohort study. MAIN EXPOSURES Dairy, calcium, and vitamin D intakes assessed by food frequency questionnaire every 12 to 24 months between 1996 and 2001. MAIN OUTCOME MEASURE Incident stress fracture that occurred between 1997 and 2004 as reported by mothers of the participants in 2004. Cox proportional hazards models were used to examine associations. RESULTS During 7 years of follow-up, 3.9% of the girls developed a stress fracture. Dairy and calcium intakes were unrelated to risk of developing a stress fracture. However, vitamin D intake was inversely related to stress fracture risk. The multivariable-adjusted hazard ratio of stress fracture for the highest vs the lowest quintile of vitamin D intake was 0.49 (95% CI, 0.24-1.01; Ptrend = .07). We conducted a stratified analysis to estimate the association between vitamin D intake and stress fracture risk among girls participating in at least 1 h/d of high-impact activity, among whom 90.0% of the stress fractures occurred, and found that higher vitamin D intake predicted significantly lower risk of stress fracture (Ptrend = .04). CONCLUSIONS Vitamin D intake is associated with lower stress fracture risk among adolescent girls who engage in high levels of high-impact activity. Neither calcium intake nor dairy intake was prospectively associated with stress fracture risk.

Prospective study of physical activity and risk of developing a stress fracture among preadolescent and adolescent girls.

OBJECTIVE: To identify predictors of developing a stress fracture among adolescent girls during a 7-year period. DESIGN: Prospective cohort study. SETTING: Adolescent girls living throughout the United States. PARTICIPANTS: A total of 6831 girls aged 9 to 15 years at baseline in the Growing Up Today Study, an ongoing prospective cohort study. MAIN EXPOSURES: Exposures were assessed by self-report questionnaires completed by adolescent girls in 1996, 1997, 1998, 1999, 2000, 2001, and 2003. The adolescent girls' history of stress fracture, including age when fracture occurred and site, were reported by their mothers, who are registered nurses, in 2004. Cox proportional hazards models were used in the analysis. Main Outcome Measure Incident stress fracture that occurred between 1997 and 2004. RESULTS: During 7 years of follow-up, 267 girls (3.9%) developed a stress fracture. Independent of age, age at menarche, family history of fracture, and hours per week of low- and moderate-impact activity, hours per week of running (hazard ratio = 1.13; 95% confidence interval, 1.04-1.23), basketball (hazard ratio = 1.12; 95% confidence interval, 1.03-1.23), and cheerleading/gymnastics (hazard ratio = 1.12; 95% confidence interval, 1.02-1.22) were significant predictors of developing a stress fracture. No other type of high-impact activity was associated with an increased risk. CONCLUSION: Girls who engage in running, basketball, cheerleading, or gymnastics should be encouraged to include varied training in lower-impact activities to decrease the cumulative amount of impact in order to minimize their risk of stress fractures.

Cadmium transport by the gut and Malpighian tubules of Chironomus riparius.

Many aquatic insects are very insensitive to cadmium in short-term laboratory studies. LC50 values for larvae of the midge Chironomus riparius are over 25,000 times the Criterion Maximum Concentration in the United States Environmental Protection Agency (U.S. EPA (2000)) species sensitivity distribution (SSD). Excretion or sequestration of cadmium may contribute to insensitivity and we have therefore examined cadmium transport by isolated guts and renal tissues of C. riparius larvae. Regional differences of Cd transport along the gut were identified using a Cd(2+)-selective microelectrode in conjunction with the Scanning Ion-Selective Electrode Technique (SIET). Cd is transported into the anterior midgut (AMG) cells from the lumen and out of the cells into the hemolymph. The transport of Cd from the gut lumen to the hemolymph exposes other tissues such as the nervous system and muscles to Cd. The gut segments which remove Cd from the hemolymph at the highest rate are the posterior midgut (PMG) and the ileum. In addition, assays using an isolated Malpighian (renal) tubule preparation have shown that the Malpighian tubules (MT) both sequester and secrete Cd. For larvae bathed in 10 micromol l(-1) Cd, the tubules can secrete the entire hemolymph burden of Cd in approximately 15 h.