Jennifer Aniston, 51, is known for her commitment to fitness. One of her tricks, she says, is to make sure that she gets a dose of vitamin C three times a day, along with regular exercise and a healthy diet.

And she's onto something, according to a peer-reviewed observational study published in the Journal of Nutrition.

Researchers looked at data from more than 13,000 people ages 42 to 82, which was part of the European Prospective Investigation into Cancer and Nutrition in Norfolk Study. They found that men and women who got the most vitamin C through their diet had more muscle mass than those who consumed the least.

True, the maximum difference was only 4% more muscle mass. But that turns out to be a lot of muscle.

Vitamin C helps preserve and build muscle because it defends cells and tissues from oxidized free radicals (the causes of inflammation) that can destroy muscle.

In the U.S., around 14% of men and 8% of women are deficient of vitamin C (putting them at risk for rickets), and many more are insufficient, making them vulnerable to everything from infections to muscle loss.

To keep and build muscle as you age, combine regular aerobic and strength-building exercise with two doses of vitamin C supplement daily — half a multivitamin containing 1,000 mg of vitamin C in the morning and again at night.

And eat around seven servings of fresh fruits (citrus is loaded with vitamin C) and vegetables (cruciferous vegetables, green and red peppers, and dark leafy greens deliver the most) daily.