Karen Rafferty

Potassium intake and the calcium economy

Background: Dietary potassium intake (K) lowers urinary calcium (Ca) excretion and, in short-term studies, may improve Ca balance. Purpose: Our objective was to assess K effects on the Ca economy under steady-state conditions. Design: 8-day, inpatient metabolic studies of nitrogen, phosphorus, and Ca balance, combined with dual isotopic Ca tracer kinetics studies. Study diet matched to prestudy nutrient intakes. Subjects: 191 single women studied from 1–5 times at ∼5-year intervals, for a total of 644 inpatient studies. Median age at time of study: 50.2 yrs; 301 studies were performed postmenopausally without hormone replacement; 343 were either premenopausal or postmenopausal but on estrogen replacement therapy. Results: Dietary K was highly significantly associated with urinary Ca excretion, with a coefficient of −0.0109 mmol urine Ca/mmol diet K. However, dietary K was negatively correlated with dual-tracer Ca absorption (coefficient for Ca absorption fraction: −0.00094/mmol dietary K), and was not associated with urine Ca after adjustment for Ca absorption. Conclusion: While a high K diet (i.e., one rich in fruits, vegetables, and dairy products) has multiple health benefits and clearly lowers urine Ca, it does not seem to exert any appreciable net influence on the Ca economy, largely because the reduced calciuria is offset by reduction of intestinal absorption. We note, however, that since the high K intakes in our studies come more from milk and meat than from fruits and vegetables, we cannot exclude a possible balance effect for different food sources of K.

Effect of Yogurt on a Urinary Marker of Bone Resorption in Postmenopausal Women

Adding three servings of yogurt to the daily diet of older women with habitually low calcium intakes resulted in a significant reduction in urinary excretion of N-telepeptide, a marker for bone resorption. Results were compared to the effects of three servings of a nutrition-poor snack and differences were apparent 7-10 days of starting the diet change. The satiety effect of the snacks resulted in a decrease in intake of other foods. The added nutrients of the yogurt improved overall diet quality substantially, while diet quality declined with the nutrient-poor snack. The results show that diets low in dairy intake are often marginal for several nutrients and that, so far as calcium is concerned, bone makes up for what the diet lacks. Moreover, bone resorption responds rapidly and sensitively to improvements in calcium intake that are readily achievable by an older female population.

Preponderance of the evidence: an example from the issue of calcium intake and body composition

Meta-analysis is typically applied to studies developed in fairly mature fields, but may be ill-suited for younger fields in which most of the evidence comes from studies that were designed for other endpoints entirely and that are often significantly underpowered for the effect in question. Here, there are no generally accepted methods for getting a grasp on the preponderance of the evidence. In this review, one way of doing so is proposed and the recently emergent literature concerning calcium intake and body composition is used as an illustration of how such an approach might be used.

The selection and prevalence of natural and fortified calcium food sources in the diets of adolescent girls

OBJECTIVE To assess the impact of calcium-fortified food and dairy food on selected nutrient intakes in the diets of adolescent girls. DESIGN Randomized controlled trial, secondary analysis. SETTING AND PARTICIPANTS Adolescent girls (n = 149) from a midwestern metropolitan area participated in randomized controlled trials of bone physiology from 1997 to 2008. INTERVENTION Subjects randomly assigned to a high-calcium (HC) diet supplying 1,500 mg calcium/d, or their usual diet (UC). MAIN OUTCOME MEASURES Dietary intake was assessed from 3-day food records and calcium intakes categorized by food source. Food group composites, representing calcium-fortified and dairy food categories, were examined for their relative nutrient contributions. Student t tests were used to evaluate differences in selected nutrient intakes between the 2 study groups. RESULTS Dairy food contributed 68% of the total mean 1,494 mg calcium/d in the HC group, and calcium-fortified food contributed 304 mg calcium. In the UC group, dairy food contributed 69% of the total mean 765 mg calcium/d and calcium-fortified food contributed 50 mg calcium. Nutrient profiles of the dairy composites differed significantly from the calcium-fortified composites (P < .05). CONCLUSIONS AND IMPLICATIONS Dairy food was the primary source of calcium selected by these adolescent girls; calcium-fortified food augmented calcium intakes.

Chronic Dietary Fiber Supplementation with Wheat Dextrin does not Inhibit Calcium and Magnesium Absorption in Premenopausal and Postmenopausal Women

This placebo-controlled, randomized, crossover clinical study examined the effect of chronic wheat dextrin intake on calcium and magnesium absorption. Forty premenopausal and postmenopausal women (mean ± SD age 49.9 ± 9.8 years) consumed wheat dextrin or placebo (15 g/day) for 2 weeks prior to 45calcium (45Ca) and 26magnesium (26Mg) absorption testing. After a standardized breakfast, serial blood and urine samples were obtained. The mean ± SD area under the curve from 0 to 9 h for 45Ca specific activity was 0.81 ± 0.21 for wheat dextrin and 0.82 ± 0.22 for placebo, showing that wheat dextrin had no effect on calcium absorption. The mean ± SD percentage excess of 26Mg/24Mg was 7.8% ± 2.1% for wheat dextrin and 7.9% ± 2.6% for placebo, showing that wheat dextrin had no effect on magnesium absorption. In conclusion, chronic wheat dextrin consumption did not inhibit calcium or magnesium absorption from the gastrointestinal tract in women.

Intake of Key Pregnancy Nutrients in Midwest Adolescents of Childbearing Potential Vitamin D, Polyunsaturated Fatty Acids, and Folate

Background. Nutrient intake in the preconception period can have profound effects on pregnancy outcomes. Pregnancy during adolescence is often unplanned and associated with lower rates of prenatal care. Poor baseline nutrition status could contribute to poor pregnancy outcomes. Design A secondary analysis of data obtained from 2 randomized controlled trials conducted from 1997 to 2007 was performed with the objective of quantifying intakes of folate, vitamin D, and polyunsaturated fatty acids (PUFAs)—nutrients potentially affecting pregnancy outcomes in adolescent girls of childbearing age. Participants. Two cohorts of girls living in a metropolitan area were analyzed. The first group, a sample of 64 healthy 9-year-old girls, was followed for 10 years. The second, a similar cohort of 134 healthy girls, was followed for 8 years. Information about nutrient intake from food sources was collected and analyzed during the times the participants were 14 to 19 years old, considered years of potential pregnancy. S...