Effects of calcium supplementation on circulating osteocalcin and glycated haemoglobin in older women
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One year of calcium supplementation in older women led to modest reductions in total osteocalcin and undercarboxylated osteocalcin (ucOC), with no changes in muscle or fat mass, or glycated haemoglobin. Future studies should explore whether treatments with more profound effects of suppressing ucOC may lead to impaired glycaemic control.
Total osteocalcin (TOC) is a marker of bone turnover, while its undercarboxylated form has beneficial effects on glucose metabolism in mice. This post hoc analysis of a randomised double-blind, placebo-controlled trial examined whether 1 year of calcium supplementation affected circulating TOC, undercarboxylated osteocalcin (ucOC) or glycated haemoglobin (HbA1c) in 1368 older community-dwelling women (mean age 75.2 ± 2.7 years).
Women enrolled in the Calcium Intake Fracture Outcome Study trial (1998–2003) were supplemented with 1.2 g/d of elemental calcium (in the form of calcium carbonate) or placebo. Circulating TOC, ucOC and HbA1c was measured at 1 year (1999).
After 1 year of calcium supplementation, TOC and ucOC levels were 17% and 22% lower compared with placebo (mean 22.7 ± 9.1 vs. 27.3 ± 10.9 μg/L and 11.1 ± 4.9 vs. 13.0 ± 5.7 μg/L, both P < 0.001). Carboxylated osteocalcin/ucOC was 6% lower after calcium supplementation (P < 0.05). Despite this, no differences in HbA1c were observed (calcium, 5.2 ± 0.6 vs. placebo, 5.3 ± 0.8%; P = 0.08). Calcium supplementation did not affect BMI, whole body lean or fat mass. In exploratory analyses, total calcium (dietary and supplemental) was inversely related to TOC and ucOC, indicating calcium intake is an important dietary determinant of osteocalcin levels.
One year of calcium supplementation in older women led to modest reductions in TOC and ucOC, with no changes in muscle or fat mass, or HbA1c. Future studies should explore whether treatments with more profound effects of suppressing ucOC may lead to impaired glycaemic control.
KeywordsBone Diabetes Lean mass Osteocalcin Vitamin K
The study was financially supported by a research grant from a Sir Charles Gairdner Hospital Research Advisory Committee, Healthway Health Promotion Foundation of Western Australia and by the project grants 254627, 303169 and 572604 from the National Health and Medical Research Council of Australia. The salary of Dr. Lewis is supported by a National Health and Medical Research Council of Australia Career Development Fellowship (ID: 1107474) and A/Prof Itamar Levinger is a Heart Foundation Future Leader Fellow (ID: 100040). None of the funding agencies had any role in the conduct of the study; collection, management, analysis, or interpretation of the data; or preparation, review, or approval of the manuscript.
Compliance with ethical standards
The Human Ethics Committee of the University of Western Australia approved the study and written informed consents were obtained from all participants. Human ethics approval for the use of linked data for the project was provided by the Human Research Ethics Committee of the Western Australian Department of Health (DOHWA HREC), project number no. 2009/24.
Conflicts of interest
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