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.

Effects of long-term moderate exercise on iron status in young women.

The impact of long-term (6-month) moderate exercise on the iron status of previously sedentary women was determined by randomly assigning 62 college-age women into one of the following four groups: 1) 50 mg.d-1 iron supplement, low iron diet (N = 16); 2) Placebo, free choice diet (N = 13); 3) Meat supplement to achieve 15 mg.d-1 iron intake (N = 13); and 4) Control, free choice diet (N = 20). All groups except the Control group exercised 3 d.wk-1 at 60%-75% of their heart rate reserve. VO2max was measured at baseline and week 24. Blood was sampled at baseline and every 4 wk thereafter for 24 wk to measure iron status and to elucidate the causes for alterations in iron status. Subjects had depleted iron stores throughout the study as indicated by their serum ferritin levels (< 15 ng.ml-1). Serum iron, total iron binding capacity and transferrin saturation were not compromised with exercise. Mean hemoglobin level in the Placebo/Ex group was significantly (P < 0.05) lower than the 50 Fe/Ex and the Meat/Ex groups by week 24. However, changes in serum albumin, haptoglobin, and erythropoietin data from the study cannot explain these changes.

Iron status in exercising women: the effect of oral iron therapy vs increased consumption of muscle foods.

Forty-seven previously sedentary women participating in a 12-wk moderate aerobic-exercise program were randomly assigned to one of four dietary groups: 50-mg/d iron supplement and a low food-iron diet (50 FE + EX), 10-mg/d iron supplement and a low food-iron diet (10 FE + EX), placebo and unrestricted diet (P + EX), and meat supplement and high food-iron diet (M + EX). A sedentary control group (n = 13) received no dietary interventions. Hematocrit, total iron-binding capacity, and hemoglobin, serum iron, serum ferritin, and serum albumin concentrations were measured every 4 wk. Hemoglobin values decreased at the end of 4 wk in all exercising groups compared with the control group. Iron status in the 50 FE + EX and M + EX groups improved after week 4 as indicated by an increase in serum ferritin, serum iron, and hemoglobin concentrations, and a decline in total iron-binding capacity. Thus, short-term, moderate aerobic exercise resulted in compromised iron status that was offset to varying degrees by ingesting iron or meat supplements. However, meat supplements were more effective in protecting hemoglobin and ferritin status than were iron supplements.

Does baseline serum total calcium level influence the blood pressure response to calcium supplementation? A double-blind study.

This was a randomized and double-blind study to examine: (1) the effect of a 1500 mg/day calcium supplement vs a placebo for 8 wk in 42 adults with high normal or mildly elevated blood pressure (BP) and, (2) the relationship between baseline serum total calcium levels and BP response to calcium supplementation. Following the experimental protocol, mean pressures were lower in the treatment vs placebo group (95.7 mmHg and 102.1 mmHg, p = 0.002), but response was not related to initial serum total calcium levels. After 8 wk of calcium supplementation, serum total calcium was greater in the treatment group compared to the placebo group (p = 0.02). Within the treatment group only, the change in total serum calcium was related to the change in parathyroid hormone (r = -0.92, p = 0.0002); and the change in ionized calcium was related to the change in parathyroid hormone (r = -0.68, p = 0.03) in the subgroup with low baseline serum total calcium. This study provides further support for the hypotensive effect of supplemental calcium in some people. However, it fails to clarify or expand upon previous reports that a low serum total calcium level might be predictive of the blood pressure response to increased calcium.

The effect of dietary interventions to reduce blood pressure in normal humans.

Changes in electrolyte intake have been advocated to lower the prevalence of hypertension in the normal population. To elucidate the potential impact of such strategies, we conducted a comprehensive analysis of data from three interventions, namely, salt (NaCl) restriction, calcium (Ca) supplementation, and potassium (K) supplementation in normal volunteers. Eighty-two adults lowered their Na intake from 157 +/- 6 S.E. to 68 +/- 3 mEq/day for 12 weeks. Population mean systolic and diastolic blood pressure decreased less than or equal to 2 mm Hg. Ca supplementation, 1.5 g daily for 12 weeks in 37 men, decreased blood pressure compared to 38 men receiving placebo. Ca supplementation, 1 g daily for 8 weeks in an older group of 44 normal subjects, decreased supine diastolic and standing systolic blood pressure. K supplementation with a nonchloride salt in 64 normal adults for 4 weeks had no effect on systolic or diastolic blood pressure even though urinary excretion was increased by 20 mmol/day. The responses to all interventions were Gaussian in distribution. A potentially adverse effect on blood pressure in some normal individuals cannot be excluded on the basis of the currently available data. Although all three interventions may benefit some hypertensive and some normal individuals, the data from these relatively short-term cross-sectional studies are insufficient to warrant generalized dietary recommendations for the normal population.

Metabolic differences between subjects whose blood pressure did or did not respond to oral calcium supplementation.

In a randomized, double-blind, placebo-controlled trial of a 1500 mg/d calcium supplement taken over a 12-wk period, the mean arterial pressure of normotensive adult males (n = 37) was modestly but significantly lowered as compared with a placebo group (n = 38). Within the Ca group only, responders (greater than or equal to 5 mm Hg decrease in mean arterial pressure, n = 14) were compared with nonresponders (less than 5 mm Hg decrease in mean arterial pressure, n = 23). The responders were older (p = 0.002) and exhibited higher mean arterial pressure (p = 0.00001), higher serum parathyroid hormone (p = 0.01), and lower serum total Ca (p = 0.001) at baseline. A stepwise discriminant function analysis revealed that mean arterial pressure and serum total Ca correctly classified 78.38% of the responders and nonresponders and, thus, were the most important determinants of blood pressure response to supplemental Ca.

Blood pressure and metabolic effects of calcium supplementation in normotensive white and black men.

A randomized, double-blind, placebo-controlled trial was conducted to examine the effect of calcium supplementation on blood pressure in normotensive black (n = 21) and white (n = 54) men, aged 19 to 52 years. After a four-week baseline period of weekly blood pressure measurement, subjects were randomly assigned within racial groups to either a treatment (calcium, 1500 mg/d) or placebo group for a 12-week period. During the experimental period, multiple blood pressure measurements were taken every two weeks in both the seated and supine positions, using a random baseline sphygmomanometer. A repeated-measures analysis of covariance yielded a modest but significantly lower seated mean arterial pressure in the treatment group compared with the control group, but no differences between the races. Results were similar for supine blood pressure. Calcium supplementation, in comparison with placebo, resulted in lower mean arterial pressure in normotensive white and black men during a 12-week period. The overall blood pressure-lowering effect was not correlated with the response of serum levels of total and ionized calcium, total inorganic phosphorus, or parathyroid hormone, or overnight urinary electrolyte values.