Review on November 07, 2008
Women who enjoy running in and training for marathons, or just like to regularly get their hearts racing, have been told for decades that these activities can wreak havoc on the menstrual cycle and cause irregular periods or even worse.
Not so fast.
A study conducted by scientists at the University of British Columbia in Vancouver found that irregular periods equally afflict women who exercise excessively and women who do not exercise at all.
These findings were in spite of the investigators' expectations as well as conventional wisdom on the subject that had existed until now.
This conventional wisdom has pointed to excessive exercise as a primary culprit of irregular periods and other menopause-related ailments. The thought is that rigorous exercise decreases the amount of fat in a woman's body. Fat helps to release estrogen, the female sex hormone, and triggers menstruation. With shrinking amounts of estrogen in their bodies, irregular periods are thought to occur. Furthermore, with less estrogen, calcium in the bones is not replenished as much or as quickly as it needs to be and bone mass is diminished. This can lead to osteoporosis, the disease that leaves bones porous and frail.
Prior to the study, similar studies had not observed exercising women and nonexercising women over time, but instead only looked at irregular periods of women who were exercise. This approach does not show cause and effect, the researchers noted.
This study took three groups of a total of 66 women between the ages of 21 and 42. One group was training for a marathon, another group was exercising at least an hour a week, and the final group was not exercising at all.
The study concluded that 80 percent of the women had irregular periods at some point during the year-long study. Many of the menstrual cycles of those who had irregular periods lacked progesterone, not estrogen. The researches hypothesized that a lack of progesterone has more to do with early stages of osteoporosis than does estrogen.
Some marathon runners report that they do have irregular periods once or twice when they first start training, but surmised that that occurs only because of the initial stress and shock the bodies goes through under those circumstances.
Regardless of the findings of this study, there are countless sources of information that maintain that exercise definitively causes irregular periods. The conventional wisdom seems to have won this race, even if hard data has not yet crossed the finish line.