Muscle mass maintenance differs in women

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 the School of Medicine and at 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,” said Bettina Mittendorfer, Ph.D., a study co-investigator and research associate professor of medicine. “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 Public Library of Science (PLoS) One, Mittendorfer and colleagues in the Division of Geriatrics and Nutritional Science and at the University of Nottingham found that postmenopausal women are less able to use protein from their diets 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 and 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 said. “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 postmenopausal women are less able to build muscle following resistance exercises like lifting weights.”

She said 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.

The researchers 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 exercises.

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.