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Older women, not men, have a hard time maintaining muscle mass

By Jim Dryden

Women over age 65 have a harder time preserving muscle than men of the same age, which probably affects their ability to stay strong and fit, according to research conducted at Washington University School of Medicine in St. Louis and the University of Nottingham in the United Kingdom.

For the first time, scientists have shown it is more difficult for older women to replace muscle that is lost naturally because of key differences in the way their bodies process food.

"It is important to maintain muscle mass throughout life to preserve strength and to reduce the risk of falls," says Bettina Mittendorfer Ph.D., a study co-investigator and associate professor of medicine at Washington University. "Falls are one of the major causes of premature death in elderly people. Half who suffer a serious fall will die within two years, so it is important to find ways to reduce those risks."

In a paper published March 26 in the journal Public Library of Science (PLoS) One, Mittendorfer and her colleagues in the Division of Geriatrics and Nutritional Science at Washington University and at the University of Nottingham found that post-menopausal women are less able to use protein from their diets in order to build muscle mass. Men of the same age were able to store more dietary protein in muscle, they report.

The researchers studied 13 men and 16 women ages 65 to 80 who fasted overnight. The next day, investigators took muscle biopsies from each of the subjects, then gave them a protein drink and an intravenous infusion of amino acids labeled with tracer molecules that could easily be detected in muscle. Three hours later, the researchers took another muscle biopsy.

"When ingesting the drink, much less protein was built in the women's muscle," Mittendorfer says. "We believe hormonal changes related to menopause may be influencing this because these differences between men and women do not occur in young individuals, and it may help explain our other preliminary research findings that show post-menopausal women are less able to build muscle following resistance exercise like lifting weights."

She says the hormone estrogen is necessary to help maintain bone mass both in women and men, and it also may play a role in preserving muscle mass. Beginning at age 50, people lose up to 0.4 percent of their muscle mass every year, making them less mobile, more prone to fractures and at risk for potentially life-threatening falls.

But the researchers say all is not lost. They suggest their findings highlight the need for older women to eat plenty of protein, such as eggs, fish, chicken and lean red meat, in conjunction with resistance exercise.

Previously, scientists have been unable to detect differences between men and women in muscle protein synthesis — the process through which the body builds muscle. But the latest research has found that in their mid- to late-60s, the female body's response to food and exercise starts to decline. Women are particularly at risk of muscle loss because they tend to have less muscle and more fat than men in early and middle age, so they are nearer to the 'danger' threshold of becoming frail when they reach their 50s and 60s.

Michael J. Rennie, Ph.D., professor of clinical physiology at the University of Nottingham, says, "Nobody has ever discovered any mechanistic differences between men and women in muscle loss before. This finding is significant for the maintenance of better health in old age and for reducing demands for health care."

Rather than eating more food, Rennie and Mittendorfer say older people should focus on eating a higher proportion of protein in their everyday diet. In conjunction with resistance exercise, that could help to reduce the loss of muscle over time. They say there also may be a case for taking hormone replacement therapy in some form to help build muscle mass, but that must be balanced against other risks associated with such treatment, including heart disease.


The full published article can be viewed in PLoS One, after the embargo lifts, at:

http://www.plosone.org/doi/pone.0001875

This study was supported by a grant from the National Institutes of Health.

Washington University School of Medicine's 2,100 employed and volunteer faculty physicians also are the medical staff of Barnes-Jewish and St. Louis Children's Hospitals. The School of Medicine is one of the leading medical research, teaching, and patient care institutions in the nation, currently ranked fourth in the nation by U.S. News & World Report. Through its affiliations with Barnes-Jewish and St. Louis Children's Hospitals, the School of Medicine is linked to BJC HealthCare.

The University of Nottingham is ranked in the UK's Top 10 and the World's Top 70 universities by the Shanghai Jiao Tong (SJTU) and Times Higher (THES) World University Rankings. It provides innovative and top quality teaching, undertakes world-changing research, and attracts talented staff and students from 150 nations. Described by The Times as Britain's "only truly global university", it has invested continuously in award-winning campuses in the United Kingdom, China and Malaysia. Twice since 2003 its research and teaching academics have won Nobel Prizes. The University has won the Queen's Award for Enterprise in both 2006 (International Trade) and 2007 (Innovation - School of Pharmacy).

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