George P. McCabe

Calcium requirements and metabolism in Chinese-American boys and girls

Calcium requirements of North American adolescents were set at 1300u2009mg/day based on data from white girls. Calcium requirements for Asian‐American adolescents have not been studied. Using metabolic balance protocols and a range in calcium intakes, skeletal calcium retention was determined in Chinese‐American adolescents. A sample of 29 adolescents, 15 boys aged 12 to 15 years and 14 girls aged 11 to 15 years, was studied twice on paired calcium intakes ranging between 629 to 1835u2009mg/day using a randomized‐order crossover design. Calcium absorption and bone turnover rates using double‐stable calcium isotope kinetic analysis on two calcium intakes per subject were measured and compared in boys and girls. Girls and boys had low habitual mean calcium intakes of 648 and 666u2009mg/day, respectively, and low mean serum 25‐hydroxyvitamin D concentrations of 19.1 and 22.2u2009ng/mL, respectively. True fractional calcium absorption varied inversely with calcium load. Boys had significantly higher bone turnover rate than girls at the same calcium intake. Calcium retention increased with calcium intake; calcium intakes to achieve maximal calcium retention were 1100u2009mg/day in boys and 970u2009mg/day in girls. Recommendations for calcium requirements should be lowered for Chinese‐American adolescents.

Bone-seeking labels as markers for bone turnover: validation of urinary excretion in rats

SummaryUrinary excretion of tritiated tetracycline (3H-TC) and 41Ca tracers was validated as reflecting skeletal disappearance of these bone-seeking tracers as a direct measure of bone turnover following ovariectomy in rats.IntroductionTritiated tetracycline (3H-TC) and Ca tracers have been used to measure bone resorption in animal models, but urinary excretion of these labels has not been directly compared to skeletal turnover. We aimed to evaluate the use of bone-seeking labels by comparing label release into urine with label in the skeleton when bone turnover was perturbed following ovariectomy.MethodsSixty-four 6-month-old ovariectomized (OVX) rats were randomized to one of eight groups in a 2u2009×u20094 design that differed in time of 3H-TC and 41Ca administration following ovariectomy (1xa0month, when bone turnover would be accelerated following estrogen depletion or 3xa0months when bone loss due to OVX had slowed down) and time of euthanasia (1xa0week, 1xa0month, 3xa0months, and 6xa0months post-dose). Twenty-four-hour urine pools over two to four consecutive days and total skeleton were collected and recovered for the assessment of 3H-TC and 41Ca.ResultsUrinary 3H-TC levels reflected skeletal 3H-TC levels (ru2009=u20090.93; pu2009<u20090.0001) over a wide range of bone turnover rates in response to an intervention. Urinary 41Ca and 3H-TC excretion were highly correlated (ru2009=u20090.95, pu2009<u20090.0001).ConclusionThis study confirms that bone-seeking label excretion into the urine directly measures bone turnover.

Calcium Intake and Age Influence Calcium Retention in Adolescence

During growth, the recommended calcium intakes should be an intake which, within the genetic potential of the individual, permits maximal skeletal accretion. This approach assumes that maximizing peak bone mass confers protection against risk of osteoporotic fracture.

Dietary Mineral Intake Ratios and Bone Health in Adults

Fruit and vegetable consumption has consistently been identified as a favorable dietary strategy for bone health. Diets high in fruits and vegetables tend to be high in several minerals that are advantageous for bone health, including potassium, calcium, and magnesium, and low in sodium. The role of calcium in bone health has been well-characterized. However, there are few studies examining the link between potassium, magnesium, and sodium and bone. Moreover, characterizing the relationships between individual mineral intakes and their ratios and health outcomes is important due to the interactive effects of these minerals. Therefore, the aim of this study was to characterize the relationships between sodium, potassium, calcium, and magnesium intake and their ratios and bone mineral density and fracture incidence in a representative sample of US adults. We used data from the National Health and Nutrition Examination Survey (NHANES), 2013–2014, for these analyses. We included adult men and women ≥40 years of age, who were not pregnant or lactating, with complete and plausible data (n = 2617). Diet was assessed using two 24-h dietary recalls. Total femur and femoral neck areal bone mineral density (aBMD) were assessed using DXA, and fracture incidence after age 20 years was determined by self-report. A model for predicting bone outcomes was developed using the following explanatory variables: age, race, height, weight, and smoking status (yes/no). Relationships between individual mineral intakes and mineral intake ratios and bone outcomes were assessed by adding each of these terms to the basic regression model separately. Body weight explained the largest proportion of the variance in total femur aBMD (29% in women, 21% in men) and femoral neck aBMD (22% in women, 15% in men), and race explained the largest proportion of the variance in fracture incidence in both women (3%) and men (2%). Sodium, potassium, calcium, and magnesium intakes were positive predictors of aBMD in men (all p 0.05). Randomized, controlled, full-feeding studies are required to determine the effect of mineral consumption from food as well as the ratio of their intakes on bone outcomes. Such findings would have important implications for making dietary recommendations and designing dietary interventions for reducing fracture risk.

Peak BMC Growth and Calcium Requirements for Children

Dietary Reference Intakes (DRIs) for calcium include the Estimated Average Requirement (EAR) and the Recommended Daily Allowance (RDA). These are estimates of the mean and the mean plus two standard deviations of the distribution of requirements for a particular subpopulation defined by sex and age. The distribution is assumed to be normal with a standard deviation that is 10% of the mean. Using longitudinal total body bone mineral content (TBBMC) data collected on a large sample of children, we have developed a parametric statistical model for the distribution of the relationship between TBBMC and age. By taking its derivative with respect to age, we obtain the distribution of the relationship between growth velocity, in terms of change in TBBMC, and age. Various other distributions are easily computed, including the distribution of the peak BMC growth velocity and the distribution of the age at peak BMC growth velocity. We use these distributions to conclude that the current procedure used to set the DRIs for calcium does not adequately take into account the variability in the patterns of growth of children due to the need for calcium associated with peak BMC growth velocity.