June 9, 2004 -- Mother Nature may play a much larger role in determining when a woman ends the reproductive phase of her life than previously thought. A new study suggests that the start of menopause may be linked to seasonal weather patterns.
Researchers found the number of women reporting their first missed period peaked in the spring months and in the autumn months to a lesser degree. The study appears in the current issue of Human Reproduction.
Researchers say seasonal variations in the reproductive functions of wild animals are well known, but this is among the first studies to look at their possible effect on humans.
"The seasonality we found seems to support the influence of environmental factors on female human reproductive functions even when they are declining," says researcher JÃ¡nos Garai, of the University of PÃ©cs in Hungary, in a news release.
Change of Life Linked to Seasonal Changes
In the study, researchers surveyed 102 women who were treated at a menopause clinic in Hungary and asked them about the month of their first missed period. Seventy-two of the women remembered the exact month their menopause process started, and 30 could remember only the season.
Researchers say the results revealed seasonal variation in the start of menopause, with a peak after the vernal (spring) equinox and a smaller peak after the autumnal equinox. The fewest number of women reported starting menopause in the summer and winter months.
Researchers say more study is needed to understand this relationship between the seasons and the start of menopause. But they suggest that melatonin, a hormone that plays a role in the circadian rhythm or 24-hour body clock, could be involved in the process.
They say melatonin is generally accepted as a signal that transmits length of day information to different processes in the body. In addition, melatonin influences ovarian hormone production. Previous research has suggested that the link between these hormones becomes disrupted as melatonin levels decline in perimenopause.
"Because of the imbalance of these factors in pre-menopause, the process eventually culminates in a point where it stumbles into irrecoverable ovarian failure," says Garai. "Length of day is likely to be only one of several factors operating and melatonin might not be the only agent involved, so we need to research this further."