Women who have sex at least once
a month have a lower risk of entering menopause early than women
with less active sex lives, scientists have found in research
which they say points to a form of biological energy trade-off.
A study of data from almost 3,000 women in the United States
showed that those who said they had sexual activity weekly or
more frequently - including intercourse, oral sex, sexual
touching or self-stimulation - were 28% less likely to have
experienced menopause at any given age than women who said they
had sex less than once a month.
"If a woman is not having sex, and there is no chance of
pregnancy, then the body 'chooses' not to invest in ovulation,
as it would be pointless," said Megan Arnot, a PhD candidate at
University College London (UCL) who co-led the research.
She said the findings lend weight to the idea that the human
menopause originally evolved to reduce reproductive conflict
between generations of females, and to allow older women to
increase their fitness through investing in their grandchildren.
Women are more susceptible to disease during ovulation
because their immune systems are depressed during this time.
Arnot said the apparent "biological trade-off" is that it
would be pointlessly costly to invest energy in the ovulation
process if a women is having little or no sex and is hence
unlikely to fall pregnant, so the body diverts energy resources
into protecting and caring for existing offspring.
"The menopause is, of course, an inevitability for women,
and there is no behavioural intervention that will prevent
reproductive cessation," said Ruth Mace, a professor of
anthropology at UCL who worked on the study with Arnot.
"Nonetheless, these results are an initial indication that
menopause timing may be adaptive in response to the likelihood
of becoming pregnant," she said
The research was published in the journal Royal Society Open
Science and was based on data from the U.S. Study of Women's
Health Across the Nation, also known as the SWAN study.