Women born in the spring are likely to go through the menopause earlier than those born in autumn, Italian researchers report. A team based at the Modena General Hospital has shown that the season in which a woman is born influences the age at which she will go through the menopause, with an average difference of 18 months between spring and autumn-born women. The researchers, who published their findings in the journal Human Reproduction, suggest that seasonal differences could affect the number of eggs a baby girl is born with.
It is thought that a woman's ovaries contain about two million egg-producing follicles at birth, but that this number falls to around 400,000 by the time she reaches puberty, and continues to drop throughout her life. Usually, one mature egg is released by the ovaries every month, until the menopause begins around the age of 50. In the latest study, the researchers studied 2,822 women who were at least a year past the menopause, and found a surprising link between the age at which menopause began and birth month. Women born in October reached the menopause at the average age of 50 years and three months, while those born in March did so at 48 years and nine months.
The association remained strong even when the team took into account other factors, such as age of first period, weight and smoking. Lead author Angelo Cagnacci said that the findings reinforced the idea that factors in the womb affected a baby's adult life. 'Mothers should be aware of this', he said, adding 'during pregnancy they are going to influence not only the health of the newborn, but also the health and reproductive life of their child during adulthood'. However, he conceded that there were some limitations to the study, such as the fact that it involved women referred to menopause centres rather than the general population, and also that the effect of the seasons may vary in different parts of the world.
The researchers suggest that seasonal differences in temperature and sunlight could influence fetal growth, as could differences in diet or exposure to infections during pregnancy. UK reproduction expert Tom Kelsey told Nature News that the result was 'amazing', adding 'I would have said the mother's body mass index would be the main variable'. He pointed out that there might not have been much difference in the birth weight of the women taking part in the study, since they were all born in the years following the war, when general nutrition was poor. Studies elsewhere might reveal a larger role for the mother's diet and weight, he said.