Weight loss and calcium intake influence calcium absorption in overweight postmenopausal women.

Abstract

BACKGROUND:

Weight loss (WL) reduces bone mass and increases fracture risk. Mechanisms regulating calcium metabolism during WL are unclear.

OBJECTIVE:

The objective was to assess the effect of 6 wk of WL at 2 different amounts of calcium intake [normal (NlCa): 1 g/d; high (HiCa): 1.8 g/d] on true fractional calcium absorption (TFCA), bone turnover, and bone-regulating hormones in overweight postmenopausal women.

DESIGN:

Seventy-three women (body mass index, 26.9 +/- 1.9 kg/m(2)) were recruited either to consume a moderately energy-restricted diet (WL group) or to maintain their body weight [weight-maintenance (WM) group] and were randomly assigned to either the HiCa or the NlCa group in a double-blind manner. Subjects underwent weekly diet counseling, and measurements were taken at baseline and after 6 wk.

RESULTS:

Fifty-seven women completed the study and had a baseline TFCA of 24.9 +/- 7.4%. Energy restriction significantly decreased the total calcium absorbed (P < 0.05) in the WL group (n = 32) compared with the WM group (n = 25; analysis of covariance). Regression analysis showed that a greater rate of weight loss suppressed TFCA and the total calcium absorbed (P < 0.05) in the HiCa group. The women in the NlCa WL group absorbed inadequate amounts of calcium (195 +/- 49 mg/d), whereas the women in the HiCa WL group absorbed adequate amounts (348 +/- 118 mg/d). Parathyroid hormone explained 22% of the variance in calcium absorbed in the NlCa group only.

CONCLUSIONS:

We suggest that WL is associated with elevated calcium requirements that, if not met, could activate the calcium-parathyroid hormone axis to absorb more calcium. Normal intakes of calcium during energy restriction result in inadequate total calcium absorption and could ultimately compromise calcium balance and bone mass.

• Authors: Mariana Cifuentes, Claudia S Riedt, Robert E Brolin, M Paul Field, Robert M Sherrell, Sue A Shapses
• Journal: The American journal of clinical nutrition (Am J Clin Nutr) Vol. 80 Issue 1 Pg. 123-30 (Jul 2004) ISSN: 0002-9165 [Print] United States
• PMID: 15213038 (Publication Type: Clinical Trial, Journal Article, Randomized Controlled Trial, Research Support, U.S. Gov't, P.H.S.)

Chemical References

• Calcium, Dietary
• Parathyroid Hormone
• Calcium

Topics

• Aged
• Analysis of Variance
• Bone Density
• Bone and Bones (metabolism)
• Calcium (metabolism)
• Calcium, Dietary (administration & dosage, pharmacokinetics)
• Diet, Reducing (adverse effects)
• Double-Blind Method
• Female
• Humans
• Intestinal Absorption
• Middle Aged
• Obesity (diet therapy, metabolism)
• Parathyroid Hormone (pharmacology)
• Postmenopause (metabolism)
• Regression Analysis
• Seasons
• Weight Loss (physiology)