As Sarah wrote, finding that first gray hair can be as discombobulating as that first wrinkle. The problem with gray hair is that the only course of action seems to be cover up rather than cure. But now scientists may have found that there is a way to prevent your hair from turning gray: exercise.

Actually, Dr. Mark Tarnopolsky, professor of pediatrics at McMaster University in Ontario, found that exercise reduced or eliminated almost every detrimental effect of aging in mice that had been genetically programmed to grow old at an accelerated pace.

In order to the experiment, Dr. Tarnopolsky and his team tinkered with the mice’s ability to repair malfunctioning mitochondria, which are tiny organelles within cells. Mitochondria can accumulate small genetic mutations, which under normal circumstances are corrected by specialized repair systems within the cell. But as we age, the number of mutations begins to outstrip the system’s ability to make repairs, and mitochondria start malfunctioning and dying.

Many scientists consider the loss of healthy mitochondria to be an important underlying cause of aging. As mitochondria start flaking out on us, the cells they fuel wither or die. Muscles shrink, brain volume drops, hair falls out or loses its pigmentation.

The mice in the test lacked the primary mitochondrial repair mechanism, aged prematurely and were dead before reaching a year of age. Except the mice that exercised.

Those mice that ran on a wheel for 45 minutes three times a week remained youthful with full pelts of dark fur, and no graying. They also had maintained almost all of their muscle mass and brain volume. At 1 year, none of the exercising mice had died of natural causes.

The experiment may help us understand how exercise helps to stave off aging. The jogging mice produced a protein called PGC-1alpha, which regulates genes involved in metabolism and energy creation, including mitochondria. Exercise also sparked the repair of malfunctioning mitochondria.

Dr. Tarnopolsky said the lesson of his experiment is that “exercise alters the course of aging.” Dr. Tarnopolsky’s students were impressed. “I think they all exercise now,” he told the New York Times.

We’ve reported before on exercise and aging. A fitness study at the University of Florida found that among participants aged 60 to 85 who performed a series of high or low intensity exercises with weights over 6 months, free radical damage increased 13% in the no exercise group and decreased 2% in the low-intensity group. Interestingly, the high-intensity weightlifting group showed a 2% increase in free radical damage. On the other hand, this group also exhibited higher bone mass, aerobic fitness, and muscle strength, as well as lower blood levels of homocysteine, a substance that can increase the risk of heart disease.