Air pollution has been linked to a drop in activity of a woman’s ovaries, researchers have revealed.

Experts say the findings suggest the female reproductive system is affected by environmental factors, although the study does not look specifically at the impact of air pollution on fertility.

However, they added that if such an effect were permanent, it might mean that women might have a shorter period of their life in which to reproduce and an earlier menopause.

“Environmental aspects of our lives matter so we should take care about indoor environments as well as external,” said the study’s lead researcher, Antonio La Marca, of the University of Modena and Reggio Emilia, in Italy.

The findings, presented at the annual meeting of the European Society of Human Reproduction and Embryology, are based on a study of levels of a hormone called AMH. This is released by cells in the ovaries and gives an indication of a woman’s ovarian reserve – the number of viable eggs the ovaries can produce. This level differs between women and is affected by a number of factors, including genetics, age and smoking. Its link to fertility is debatable: a low ovarian reserve does not necessarily mean natural conception will be difficult.

However, La Marca said previous studies had suggested there could be a link between higher air pollution and reduced fertility in women, and animal models have inferred air pollution could affect levels of AMH.

To explore the issue further, La Marca and colleagues looked at AMH levels in about 1,300 women, the samples being collected in Modena between early 2007 and autumn 2017. From the participants’ home addresses, the team estimated daily levels of small particulates known as PM2.5s and PM10s, as well as levels of nitrogen dioxide.

For women over the age of 25, levels of AMH in the blood fell with age. After taking age into account, though, the team found AMH levels were lower among women who lived in areas with higher levels of air pollutants.

Q&A How does air pollution affect the human body? Show Air pollution has been described as the ‘new tobacco’ by the head of the World Health Organization. Over 90% of the world’s population suffers toxic air and research is increasingly revealing the profound impacts on the health of people, especially children. Children and babies’ developing bodies are most at risk from toxic air, with 300 million living in places where toxic fumes are six times above the international guidelines.

A comprehensive global review found that air pollution may be damaging every organ and virtually every cell in the human body. It causes issues from heart and lung disease to diabetes and dementia, and from liver problems and bladder cancer to brittle bones and damaged skin. The systemic damage is the result of pollutants causing inflammation that then floods through the body, and from ultrafine particles being carried around the body by the bloodstream. A Canadian study recently linked air pollution nanoparticles to brain cancer for first time In the UK, while deaths attributed to air pollution have halved in the last four decades, most urban areas have illegal levels of air pollution. One in 20 deaths in the UK is still attributable to small particle pollution alone.

Damian Carrington, Environment editor

More specifically, when the team split the air pollution levels into four bands, they found women living amid the worst pollution were two to three times more likely than those in the other bands to have AMH levels below 1ng/ml – a level the team say signifies a severely low ovarian reserve. La Marca said previous research had shown only about 10% of healthy women under the age of 30 had such low levels of AMH.

La Marca said while the link between AMH levels and the chances of becoming pregnant naturally in the short term remained unclear, the results suggested environmental factors could play a role in female reproductive health.

“Having a high AMH is in some way a reproductive advantage because women with a higher AMH are going to have a longer reproductive lifespan,” he said, adding it was also significant to those undergoing IVF. “If you have a high AMH you will have a higher number of eggs after ovulatory stimulation which turn into a higher number of embryos,” he said.

The study has limitations, not least that the team was unable to take into account other factors, such as poverty and poorer health, that tend to be more prevalent in areas of high pollution and might also affect AMH levels. What’s more, AMH and pollution levels were not tracked over time.

Richard Anderson, a professor of clinical reproductive science at the University of Edinburgh, said while the impact of environmental factors on sperm count and quality was a topic of much research, there had been far less work on possible impacts on the female reproductive system.

“This does show a reduction in the activity of the ovaries in women [living in areas of high air pollution],” he said, although he pointed out the levels of air pollution women were directly exposed to was not measured.

Anderson said questions remained. “There is uncertainty in whether this is a permanent effect, which might indicate perhaps a reduced reproductive lifespan and an earlier menopause, or whether this is a temporary effect that women could recover from if they are no longer exposed to those chemicals,” he said.