Impact of exercise on bone health and contraindication of oral contraceptive use in young women.

PURPOSE: The effect of quantified resistance and high impact exercise training on bone mass as modified by age and oral contraceptive (OCont) use in young women was studied. METHODS: Women were categorized by age (18-23 vs 24-31 yr) and OCont use, and were then randomized into either three sessions of resistance exercise plus 60 min.wk-1 of jumping rope or a control group for 24 months. Total body, spine, femoral neck, greater trochanter, Ward's area, and radial bone mineral density (BMD) and/or content (BMC), biochemical markers of bone turnover, dietary intake of calcium, lean body mass, maximal oxygen uptake, and strength were determined at baseline and every 6 months. RESULTS: Total body (TB) BMC percent change from baseline was higher in exercisers compared with nonexercisers at 6 and 24 months. OCont users had lower bone turnover at baseline and a decrease in TBBMC from baseline compared with non-OCont users at 24 months. Spine BMC and BMD decreased in the exercise and OCont group at 6 months and remained significantly below nonexercisers who used oral contraceptives at 2 yr. Femoral neck BMD also decreased in the exercise and oral contraceptive group at 6 months. CONCLUSIONS: Exercise prevented a decline in TBBMC seen in the nonexercisers. On the other hand, exercise in oral contraceptive users prevented the increase observed in the spine of the nonexercise plus OCont group.

Choices for achieving adequate dietary calcium with a vegetarian diet.

To achieve adequate dietary calcium intake, several choices are available that accommodate a variety of lifestyles and tastes. Liberal consumption of dairy products in the diet is the approach of most Americans. Some plants provide absorbable calcium, but the quantity of vegetables required to reach sufficient calcium intake make an exclusively plant-based diet impractical for most individuals unless fortified foods or supplements are included. Also, dietary constituents that decrease calcium retention, such as salt, protein, and caffeine, can be high in the vegetarian diet. Although it is possible to obtain calcium balance from a plant-based diet in a Western lifestyle, it may be more convenient to achieve calcium balance by increasing calcium consumption than by limiting other dietary factors.

Previous milk consumption is associated with greater bone density in young women.

BACKGROUND: Dietary calcium and milk intakes at specific ages may influence bone mineral measures at specific sites during development of peak bone mass. OBJECTIVE: Relations of previous milk intake and current calcium intake to current bone mineral measures were investigated in young women. DESIGN: A food-frequency interview and recall of previous milk intake from early childhood to 12 y of age and during adolescence (13-19 y) were completed in a cross-sectional analysis in young women (age 18-31 y; n = 224). Three levels of previous milk intake were defined: 1) infrequently or never, 2) sometimes, and 3) at every or almost every meal. Total body (TB), femoral neck, radius (R), and spine (S) bone mineral density (BMD) and bone mineral content (BMC) were determined by using dual-energy X-ray absorptiometry. RESULTS: Childhood and adolescent milk intakes were positively correlated (r = 0.66). Childhood and adolescent milk intakes correlated with current calcium intakes (r = 0.26 and 0.33, respectively). Adolescent milk intake correlated with RBMD (r = 0.16). When weight was controlled for, adolescent milk intake correlated with TBBMD (r = 0.16), TBBMC (r = 0.21), SBMC (r = 0.16), RBMD (r = 0.18), and RBMC (r = 0.15). Current calcium intakes correlated with SBMC (r = 0.17). Regression analyses supported these results. CONCLUSIONS: Results were consistent with the hypothesis that higher milk intake during adolescence is associated with greater total body, spine, and radial bone mineral measures during development of peak bone mass, whereas current calcium intakes may influence SBMC. In addition, milk intake at a younger age may contribute to similar habits of milk intake later in life.

Dietary calcium, protein, and phosphorus are related to bone mineral density and content in young women.

BACKGROUND: Dietary factors have been implicated in modifying bone health, although the results remain controversial, particularly in young women. OBJECTIVE: The objective of the study was to determine relations of selected dietary factors and anthropometric measurements to bone mineral density (BMD) of the spine, femoral neck, trochanter, Ward's triangle, radius, and total body and the bone mineral content (BMC) of the spine, radius, and total body. DESIGN: The study was a cross-sectional analysis of 215 women aged 18-31 y. RESULTS: Weight, height, and lean mass were correlated with bone mineral measures at every site (r = 0.17-0.78). Postmenarcheal age (years since onset of menses) was positively correlated with total-body BMD and BMC, radius BMD and BMC, and spine BMC, and negatively correlated with Ward's triangle BMD. Radius BMD was correlated with protein, calcium, and phosphorus intakes, and spine BMD and BMC were correlated with energy, protein, calcium, and phosphorus intakes. These correlations remained significant when postmenarcheal age, lean mass, and fat mass were controlled. A pattern emerged in multiple regression analyses that showed a complex relation among calcium, protein or phosphorus, and the calcium-protein or calcium-phosphorus ratio and spine or total-body BMC and BMD. All 3 variables (calcium, protein or phosphorus, and calcium-protein or calcium-phosphorus ratio) were required in the model for significance. CONCLUSIONS: Anthropometric measures were predictors of bone mass. A single ratio of calcium to phosphorus or protein did not optimize bone mass across the range of calcium intakes.

Previous physical activity relates to bone mineral measures in young women.

Exercise may increase accretion of bone, potentially reducing the risk of osteoporosis. Previous physical activity was assessed in 204 minimally active young women (18-31 yr). Bone mineral content (BMC) and bone mineral density (BMD) for the total body, femoral neck, and spine were assessed by a dual x-ray absorptiometer, and the radius by a single photon absorptiometer. Self-reported occupation and leisure activity for the 5 yr before enrollment in the study, as well as high school and college sports participation, were assigned energy expenditure (EE) values. From this information, EE variables were created as follows: 1) occupation EE + leisure EE + high school sport and/or college sport EE if within prior 5 yr (5-yr EE); 2) occupation EE + leisure EE (occupation + leisure EE); and 3) high school sport EE (high school EE). These variables were correlated with bone mineral measures and significant results follow (P < 0.05). Five-year EE and occupation + leisure EE correlated with all measures of bone health (r from 0.13 to 0.39). High school EE correlated with total body BMD (r = 0.25) and BMC (r = 0.28), femoral neck BMD (r = 0.28), radius BMC (r = 0.20), as well as spine BMD (r = 0.20) and BMC (r = 0.27). When weight was controlled, 5-yr EE and occupation + leisure EE remained correlated with all BMC measures (r from 0.14 to 0.22). When controlled for weight, high school EE remained associated with femoral neck BMD (r = 0.24), total body BMD (r = 0.20) and BMC (r = 0.26), and spine BMC (r = 0.17). To partially control for selection bias, data were also controlled for total body BMD. Five-year EE and occupation + leisure EE remained positively correlated with all measures of BMC. High school EE remained correlated both with femoral neck BMD and total body BMC. In multiple regression analyses, 5-yr EE or occupation + leisure EE were significant predictors of all measures of bone health, except femoral neck BMD. High school EE was a significant predictor for total body BMD and BMC, femoral neck BMD, and spine BMC.

Peak bone mass in young women.

Increasing peak bone mineral density (BMD) or content (BMC) in young women may help to reduce the incidence of osteoporosis. Identifying the age when peak bone content or density is attained is essential to develop strategies aimed at optimizing peak BMD and BMC. Total body bone mineral density (TBBMD) and content (TBBMC) were measured by a dual X-ray absorptiometer in healthy females (n = 247, aged 11-32 years). TBBMD and TBBMC were modeled separately as a nonlinear function of age. By age 22.1 +/- 2.5 years, 99% of peak BMD is attained, and by age 26.2 +/- 3.7 years, 99% of peak BMC is attained. Nonlinear relationships between weight and TBBMD or TBBMC were also modeled. In this model, the influence of several parameters, including age, weight, and height, on BMC and BMD were simultaneously assessed. A model with age and weight described the best fit for TBBMD, whereas age, weight, and height described the best fit for total body TBBMC.