Women who live by polluted roads could become infertile younger, a study has found.
Hormone tests suggest those living in polluted areas were three times more likely to have a low number of eggs in their ovaries.
Experts say women planning to have a family should consider moving out of the city to slow down their biological clock.
Women are born with a certain number of eggs which slowly deplete over time.
The greater “ovarian reserve” is seen as a measure of how long a woman will be able to bear children.
The Italian study of more than 1,300 women tested their blood for a hormone which may identify those with few eggs left to get pregnant.
Prof Antonio La Marca, who led the study from the University of Modena, said: “If this is true, then air pollution can be seen as a reproductive disadvantage.
“I would suggest women think twice where to live. We probably cannot escape a city, but we can take time to think where to live in a city.”
Experts argue women should be warned about the risk of spending your younger years living next to a busy road.
Particles are inhaled and get into the bloodstream, where they are able to reach the ovaries and may damage the cells protecting eggs, causing them to die.
The findings are published at the annual meeting of the European Society of Human Reproduction and Embryology (ESHRE) in Vienna.
Almost two-thirds of the women studied lived in areas exposed to high levels of toxic smog.
The study looked at levels of nitrogen dioxide and levels of dangerous tiny particles called PM10 and PM2.5s in the northern Italian city of Modena.
Prof Nick Macklon, a medical director of London Women’s Clinic, said: “These results suggest that pollution can speed up biological ageing.
“Exposure to these toxins might have similar effects on women’s long-term fertility to those we see from smoking.
“With high enough exposures, they might reduce the amount of time they are fertile.
“That is something women should be mindful of, if they are exposed to pollution day in day out.”
The study used a blood test which estimates the number of sacs in the ovaries that release eggs.
The test is one of the best measures to indicate those women who have few eggs left.
It can flag up women closer to running out who may be unable to have a child in their late thirties and early forties.
Prof Richard Anderson, of Edinburgh University, said: “These are important results.
“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.
“Smoking can put women through the menopause early and if pollution has a similar effect, that highlights the need for better public health measures to protect against it.
“We are all exposed to pollution to a greater or lesser extent and this study shows a substantial effect on female reproduction, although there may be other factors involved.”
In areas with high levels of nitrogen dioxide, which comes principally from diesel cars and industry, women were 3.3 times more likely to have a low ovarian reserve.
More than 50% of these low fertility women lived in an area with a high level of nitrogen dioxide. Fewer than 38% living in areas with the lowest level.
Areas with high levels of PM10 and PM2.5s pollution particles were home to almost two-thirds of the low egg women.
Exposure to high levels of this pollution raised women’s chances of having a low number of eggs by 3.2 times and almost two times respectively.
These were levels of pollution which fell below those judged harmful by the EU.
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