Women who live in areas with high pollution may risk experiencing an early menopause, two studies have suggested.
Researchers fear breathing in toxic air disturbs a crucial hormone which regulates the number of eggs in the ovaries.
The findings are believed to be the first to show exposure to pollutants, such as nitrogen dioxide from car fumes, ‘severely reduce ovarian reserves’.
Scientists have now suggested there pollution may shorten a woman’s opportunity ‘to achieve a family’ and boost the odds of an early menopause.
For the first study, Italian scientists took blood tests to analyse the levels of anti-Mullerian hormone (AMH) in 1,318 women.
The hormone, secreted by cells in the ovary, is used by many IVF clinics to gauge a woman’s chances of getting pregnant. Levels get lower as women get older, and it is also affected by smoking and diet.
Low levels typically indicate the woman has a poor ‘ovarian reserve’ – the number of resting immature eggs, or follicles.
The levels of AMH among the women, living in Modena in Italy between 2007 and 2017, were then compared with their addresses.
The researchers then used a computer analysis to assess the daily exposure to pollutants of each woman.
Around six in ten women whose homes were on busy roads were at risk of infertility because they had low AMH.
In comparison, the rate among women residing in less congested areas was fewer than four in ten.
Results showed, as the scientists at the University of Modena expected, that AMH levels declined after women turned 25.
However, a link was found between lower AMH levels and daily expose to pollutants – irrespective of how old the women were.
The scientists suggested pollution may speed the ageing of women’s reproductive systems, The Times reports.
Richard Anderson, professor of clinical reproductive medicine at the University of Edinburgh, said on the findings: ‘While this does not suggest a short-term problem for women trying to fall pregnant, it might indicate that women exposed to high levels of pollution might have a shorter opportunity to achieve a family, and even an earlier menopause.’
The link was uncovered after the participants were divided into four groups reflecting average daily PM10, PM2.5 and NO2 concentrations.
The analysis found significantly lower levels of AMH in women exposed to the most pollutants, compared to the bottom 25 per cent.
Some 62 per cent of women in the group exposed to the most pollution had a severe reduction in their ovarian reserves.
In comparison, results of the study revealed the figure was 38 per cent in the other three groups, on average.
The lowest AMH levels were found in women regularly exposed to levels of PM10, PM2.5 and NO2 above 29.5, 22 and 26 mcg/m3, respectively.
These values are well below the limits deemed harmful by EU guidelines of 40, 25 and 40 mcg/m3, respectively.
Professor Antonio La Marca calculated this meant women in polluted areas are up to three times more likely to have a ‘severely reduced ovarian reserve’.
‘The influence of age and smoking on AMH serum levels is now largely accepted. But a clear effect of environmental factors has not been demonstrated so far,’ he said.
‘Living in an area associated with high levels of air pollutants in our study increased the risk of severely reduced ovarian reserve by a factor of two or three.’
The findings were presented at the 35th meeting of the European Society of Human Reproduction and Embryology in Vienna.
The second study, by Harvard University scientists looking at more than 632 women at a fertility clinic, was published in Epidemiology.
Its results showed those women living in areas with high levels of fine particle PM2.5 also had lower ovarian reserves. Lead researcher Dr Audrey Gaskins said pollution seems to have a ‘strong’ effect on reducing fertility.
Experts generally agree that AMH is an indication of fertility, and a reduced chance of live birth has been reported in some studies in women with low AMH.
But some studies show while hormones such as AMH do likely reflect a woman’s ovarian reserves, the number of eggs she has left does not affect her fertility.
Other factors such as smoking, body weight and long-term hormonal contraception are recognised as having an impact on AMH levels, too.