Your environment influences your health. Take air pollution, for instance: less than stellar air quality can cause depression, slash your life span, and damage heart health.
For reproductive diseases like endometriosis — a common but debilitating chronic condition affecting 190 million women and those assigned female at birth globally — there’s no known exact cause, but there’s some science suggesting it could be environmental.
In a study published Monday in the journal Human Reproduction, researchers at Michigan State University (MSU) report that women with a history of endometriosis had higher levels of the metal cadmium, a toxic metal found in industrial pollution with no biological function in the body. This finding is only an association, not necessarily a correlation, and warrants further investigations into how contaminants and other potentially harmful substances can influence reproductive health.
“Despite the adverse impact of endometriosis on quality of life, it remains an understudied condition,” Kristen Upson, the paper’s senior author and assistant professor of epidemiology and biostatistics at the MSU College of Human Medicine, said in a press release.
Cadmium is a soft, malleable bluish-white metal naturally found in Earth’s crust, although not in vast quantities. (There’s about one-fifth of a gram in every ton of crust). Despite the low risk of getting naturally exposed, human activity is upping the amount of cadmium circulating in the environment through mining, metal processing, and other industrial processes. We may unwittingly absorb cadmium from breathing in contaminated air and eating contaminated plant- and animal-based foods. In a 2019 report, the World Health Organization classified cadmium exposure as a major public health concern.
While the toxic metal has known estrogen-like qualities and has been linked to endometrial cancer, its link with endometriosis hasn’t been clear-cut, according to past studies. For their study, the MSU researchers combed through the National Health and Nutrition Examination Survey (or NHANES), a decades-long program of studies conducted by the National Center for Health Statistics designed to assess the health and nutritional status of adults and children in the US.
They looked through data collected between 1999 and 2006, pinpointing from a pool of 41,000 individuals between the ages of 20 to 54 who had an endometriosis diagnosis and their urine cadmium levels checked. Those who met the criteria were divided into four groups based on urine cadmium levels — the first group with the lowest exposure (0.15 nanograms per milliliter) and the fourth with the highest (greater than or equal to 0.38 nanograms per milliliter).
The researchers did some statistical analysis and found individuals in the second and third groups were twice as likely to be diagnosed with endometriosis compared to the first group. For the fourth group, there was a 60 percent increased risk of endometriosis with urine cadmium levels.
The researchers note there are some limitations to their study such as the fact the data analyzed — urine cadmium levels and the history of endometriosis diagnosis — were collected at a single point in time in the past. There also may be other co-existing gynecological conditions related to or influenced by cadmium exposure like uterine fibroids or pregnancy loss, but it’s challenging to rule out those since NHANES didn’t collect information on those conditions. It’s also unclear if the cadmium exposure was due to something like tobacco smoking since the metal is present in tobacco.
Nevertheless, the researchers believe their study offers insight into how our meddling with the environment has unseen consequences, Mandy Hall, the study’s first author and an epidemiology researcher in MSU’s Department of Epidemiology and Biostatistics, said in a press release.
“By looking at environmental risk factors such as metal cadmium, we are moving the needle closer to understanding risk factors for this condition,” said Hall.
