Women with higher exposure to heavy metals may have fewer eggs in their ovaries as they near menopause compared to others the same age, a condition linked to hot flashes, weak bones, heart disease, and other health problems, according to a new study in more than 500 middle-aged women.
Exposures to cadmium, arsenic, and mercury, in particular, were linked to lower levels of a hormone that strongly correlates with the number of eggs left in a woman’s ovaries, according to the study, which was published Jan. 25 in The Journal of Clinical Endocrinology & Metabolism.
“Our findings suggest that even low exposure to these ubiquitous metals may influence women’s reproductive health,” said Sung Kyun Park, a professor of epidemiology and environmental health science at the University of Michigan and an author of the study.
“Although individual women may reduce exposure by avoiding foods contaminated with toxic metals and limiting the use of the known sources of metals, a more important approach is to reduce exposure at the population-level through legislation and regulations,” he added.
While heavy metals are known to have toxic effects on the reproductive system, little research has investigated whether exposure to low levels of these metals can influence how many eggs women have in their ovaries as they approach menopause, which begins for most women between the ages of 45 and 55.
“Epidemiological evidence is scanty,” said Park, noting that studies relying on animal models have shown a potential link between toxic metals and altered ovarian function.
The research adds to prior studies on the effects of other environmental exposures on menopause and reproductive aging in women. Exposure to 15 toxic chemicals commonly found in household products or the environment, including polychlorinated biphenyls (PCBs), pesticides, and phthalates, was linked with menopause beginning two to four years earlier, according to a 2015 study that surveyed over 1,400 menopausal women who had been tested for endocrine-disrupting chemicals.
More recently, a 2022 review found links between earlier onset of menopause and exposure to per- and polyfluoroalkyl substances (PFAS), a class of thousands of human-made chemicals found in the blood of 97% of Americans, as well as certain pesticides and phthalates. Phthalate exposure was also linked to more severe menopause symptoms.
To better understand how exposure to heavy metals affects women’s health as they approach menopause, Park and colleagues analyzed data from 549 women in their 40s and 50s who participated in the Study of Women’s Health Across the Nation (SWAN) and had varying levels of arsenic, cadmium, mercury or lead in their urine. The researchers analyzed blood tests for anti-Müllerian hormone (AMH), which corresponds with ovarian reserve, taken up to 10 years before the women had their final menstrual periods.
They found that women with the highest urinary concentrations of arsenic had about 32% lower AMH levels at their final menstrual period and those with the highest concentrations of mercury had about 41% lower AMH. Higher levels of cadmium and mercury in the women’s urine were linked to faster rates of decline in AMH as the women transitioned to menopause.
“It is important to evaluate if toxic metals also worsen the menopausal symptoms such as hot flashes,” he added. Since SWAN also assessed the women’s menopause symptoms over time, the team plans to explore this link in the near future, he said.