Women who spend a lot of time exercising or eat a heart-healthy diet appear to reach menopause earlier, according to a Japanese study - findings that researchers say could be important for cancer prevention.

Researchers led by Chisato Nagata at Gifu University tracked more than 3,100 premenopausal women over 10 years. Those who exercised the most, about eight to 10 hours a week, were 17 percent more likely to start menopause during the study than their sedentary peers.

Similarly, women who at the most polyunsaturated fats, found in many fish and vegetable oils, were 15 percent more likely to reach menopause than those who got the least.

During menopause, a woman's ovaries stop producing eggs and she can no longer get pregnant. It usually begins between ages 41 and 55.

For the study, Nagata and colleagues gave food and activity questionnaires to women aged 35 to 56 at baseline. Over the neat decade, nearly 1,800 of them went through menopause.

Although it was unclear how old they were when that happened, the findings - published in the journal Menopause - suggested that very active women and those getting lots of polyunsaturated fats have a higher chance of reaching menopause earlier.

Doing so means women have less exposure to high estrogen levels, said JoAnn Manson, president of the North American Menopause Society. Estrogen promotes breast tumors, and that may explain why early menopause is tied to a lower risk of breast cancer.

On the other hand, early menopause has also been linked to increased risks of heart disease and bone thinning, she added.

"I wouldn't want women to be concerned that they would be at higher risk of cardiovascular disease or osteoporosis if they make lifestyle modifications," she said.

"The benefits far outweigh any risks."

Other studies on menopause have been contradictory. For examples, high levels of physical activity - usually five or more hours of exercise a week - have been tied to early menopause. But they've also been linked to irregular menstrual cycles, which could lead to later menopause.

Even in the latest study, researchers said the relation between exercise and timing of menopause was "small to null."

Total fat as well as saturated fat, which comes largely from animals, didn't have any effect on the timing of menopause, Nagata and colleagues said.

Manson, who is also at the Harvard Medical School, said physical activity lowers estrogen levels, and that may be why it's linked to the early onset of menopause.

"The take home message from this study is that regular physical activity and regular heart-healthy patterns are advisable for reducing the risk for several hormone-related cancers and osteoporosis," she said.

"It's a modest effect, but it matters."