One reason may be that physical activity lowers estrogen levels but the association is unclear.
Researchers tracked 3,100 premenopausal women over 10 years. Those who worked out eight to 10 hours a week were 17 percent more likely to start menopause early. Those who ate the most polyunsaturated fats, which are found in fish and vegetable oils, were also 15 percent more likely to experience earlier menopause.
These healthy activities, however, are also linked to reduced risk of hormone related cancers and osteoporosis.
Researchers say the findings in the journal "Menopause" could be important for cancer prevention.