Calcium Reverses Fracture Risk Associated With Diet High in Animal Protein
By Nancy A. Melville
Medscape Medical News
September 15, 2009 (Denver, Colorado) — Research has shown that the intake of calcium can help mitigate the increased risk for hip fracture that is associated with the dietary intake of high levels of protein, but a new study suggests that calcium's benefits may even be more significant than realized. Calcium supplements could potentially result in a striking reversal of the fracture risk that comes with high protein intake, investigators announced here at the American Society for Bone and Mineral Research 31st Annual Meeting.
Protein intake is believed to affect bone health by causing an increase in calcium secretion, resulting in a negative calcium balance. However, protein has also been shown to increase intestinal calcium absorption.
To better gauge the role of calcium in a high-protein diet, researchers evaluated data on 1752 men and 1972 women enrolled in the Framingham Offspring Study who completed a food frequency questionnaire either between 1990 and 1994 or from 1995 through 1999. The participants were followed up for hip fracture until 2005.
The researchers estimated the participants' intake of total protein, energy, calcium, vitamin D, alcohol, and caffeine. Participants were grouped by protein intake, whether the source was animal or plant, animal:plant protein ratios, and total protein intake, with adjustments for total energy intake.
"We chose to examine protein intake from different sources because studies have shown that absorption of protein can vary depending on the source of protein," study coauthor Shivani Sahni, PhD, told Medscape Ob/Gyn Women's Health.
The results were striking. Among those who had low calcium intakes (<800 mg per day), the group with the highest intake of animal protein had a risk for hip fracture that was 2.84 times greater than the risk for fracture in the group with the lowest intake of animal protein.
Meanwhile, among those with a higher calcium intake of more than 800 mg per day, the tertile with the highest consumption of animal protein had a rate of hip fracture risk that was in fact 85% lower than the risk in the lowest animal protein intake group.
"In the group with low calcium intake, subjects in the highest tertile of animal protein intake had significantly more fractures compared to the other tertiles," said Dr. Sahni, who is a postdoctoral fellow in aging and musculoskeletal research at the Institute for Aging Research at Harvard Medical School in Boston, Massachusetts.
"Contrastingly, in the group with high calcium, subjects in the highest tertile of animal protein intake had significantly low hip fractures, compared to the rest of the group," she reported. The findings shed important light on the role of calcium intake with a high-protein diet. "Total calcium intake modifies the association of protein intake and the risk of hip fracture," Dr. Sahni concluded. "Increased animal protein intake may be productive with a high calcium intake of 800 mg or more, but the effect may be reversed with an intake of less than 800 mg."
The researchers did not find a significant association between total protein intake and animal:plant protein ratio and the risk for hip fracture.
Although the specific mechanisms behind calcium's apparent ability to offset the fracture risk associated with a high protein intake remain undetermined, the study offers further evidence of potential benefits in combining the 2 in a diet, said E. Michael Lewiecki, MD, clinical assistant professor of medicine at the University of New Mexico School of Medicine, Albuquerque.
"Although the conclusions in this study are limited due to the observational nature of the study, adequate intake of protein, as well as calcium and vitamin D, are probably reasonable recommendations for all," commented Dr. Lewiecki.
"This is an interesting study that suggests that good nutrition is good for skeletal health, and that there may be important interactions among various nutritional factors," he added. "The nature of the interaction between protein and calcium intake is not explained in this report and is an area of interest for future investigation."
The researchers received no funding for the study. Dr. Lewiecki has disclosed no relevant financial relationships.
American Society for Bone and Mineral Research 31st Annual Meeting: Abstract 1056. Presented September 12, 2009.
