The idea that too much exercise can trigger early menopause is a myth, a new report concludes.
A study of more than 107,000 women found no link between physical activity levels and the age at which they stopped menstruating.
It comes seven years after a controversial Japanese research paper found that women who spend a lot of time exercising are more likely to go through the change of life in the 1940s, or even earlier.
Despite the skepticism, the researchers have had problems conclusively contradicting the findings.
But now, researchers at the University of Massachusetts say they have found clear evidence to the contrary with the most extensive and extensive analysis on the subject, using data from American nurses that were followed for more than two decades.
The study of the EE. UU It is the first conclusive evidence against a Japanese research work in which it was found that women who spend a lot of time exercising are more likely to go through the change of life in their 40s.
Lead author Elizabeth Bertone-Johnson, professor of epidemiology, said: "Our study provides considerable information to help us understand the relationship between activity and the time of menopause.
"This is due to its size, its focus on early menopause specifically, and because of its prospective design, which limits the likelihood of bias and allows us to observe physical activity at different time periods."
So far, there have been contradictory results with some studies suggesting that very active women may have a lower risk of menopause before age 45, while others have found evidence of the opposite effect.
The problem has important implications for health.
An early menopause increases the risk of developing diabetes, cardiovascular diseases and osteoporosis due to the loss of estrogen.
On the other hand, the hormone promotes breast tumors, and that may explain why early menopause is linked to a lower risk of breast cancer.
Dr. Bertone-Johnson's team also discovered that a diet high in vegetables, cheese and yogurt, which are rich in calcium and vitamin D, reduces the risk of early menopause.
Menopause, which occurs on average at the age of 51, occurs when the body naturally stops producing estrogen and other sex hormones.
During menopause, a woman's ovaries stop producing ova and can no longer conceive naturally.
It is believed that about 80 percent of these women experience symptoms, which generally last about four years, including depression, hot flushes, headaches and night sweats.
While high levels of physical activity (typically five or more hours of exercise per week) have been linked to early menopause, they have also been linked to irregular menstrual cycles, which could lead to subsequent menopause.
Dr. Bertone-Johnson said: "Several well-designed previous studies have found suggestions that more physical activity is associated with advanced age at menopause, but even in those studies the effect size was very small.
"Our results, along with other studies, provide substantial evidence that physical activity is not significantly associated with early menopause."
A previous Japanese study of more than 3,000 participants found that those who exercised the most – about eight to 10 hours per week – were 17 percent more likely to experience early menopause than sedentary couples.
The new research published in the medical journal Human Reproduction involved more than 30 times more individuals who were tracked for more than twice as long, from 1989 to 2011.
The registered nurses were between 25 and 42 years old when they enrolled in the Nurses & # 39; Health Study II and completed questionnaires about lifestyles and medical conditions every two years.
They were asked about the time they spent in recreational physical activities, such as walking, running, biking, racquet sports, swimming laps, aerobic activities, yoga, weight training and high-intensity activities such as mowing the lawn.
The researchers also collected information on factors such as race, ethnicity, age, education, height, age at which they had their first periods and whether they had been pregnant and how often.
They were also asked about the use of oral contraceptives and hormone therapy, their smoking history, weight and body mass index (BMI), diet and the use of dietary supplements.
In order to assess the frequency, duration and intensity of activities, the researchers multiplied the hours per week of each activity by their equivalent metabolic score (MET) to create total MET hours per week.
MET (Metabolic Equivalent of the task) is a measure of the energy consumed per hour. A MET score of one is the type of energy you would spend watching television.
Everything that scores above three counts as moderate activity. More than six and you're in the realms of "vigorous".
During more than 20 years of follow-up, 2,786 women experienced natural menopause before age 45.
There were no significant differences in risk between, for example, those who reported less than three MET hours per week of physical activity or 42 or more.
The latter would be equivalent to four or more hours of running or eight or more hours of walking a week.
The amount of physical activity reported in his adolescence was also not related to the risk of early menopause.
The first author Mingfei Zhao, a graduate student, said: "While our results do not suggest that increased physical activity is associated with a lower risk of early menopause, we would encourage pre-menopausal women to be physically active, since exercise It is associated with a range of health benefits, such as a lower risk of heart disease, diabetes, breast cancer and other conditions.
"Our results in no way suggest that premenopausal women should not be physically active."
Researchers are still investigating other factors that may play a role in women experiencing early menopause.
"Our work has suggested that environmental factors are associated with early menopause," said Dr. Bertone-Johnson.
"We found a higher intake of calcium and vitamin D from dairy products that is associated with lower risk.
"A higher intake of vegetable protein was also associated with lower risk, although animal protein was not.
"Cigarette smoking is associated with a higher risk, since it is underweight, and we are currently investigating other factors as well.