Endometriosis, a reproductive disorder that affects around 89 million women worldwide, can cause debilitating symptoms that lead sufferers to question “why is this happening to me?” Though there is no definitive cause nor cure for endometriosis, research has uncovered multiple potential contributing factors. A new body of research is examining a possible connection between the development of endometriosis and heavy metals exposure.
What is endometriosis?
Endometriosis, or “endo,” refers to the growth of endometrial-like tissue (similar to the tissue that lines the inside the uterus) on the outside of the uterus or on other surrounding abdominal and pelvic organs or structures. This leads to a painful build up of blood and scar tissue during menstruation, among many other symptoms. While treatment options for endo exist, there are no definitive cures thus far. And, in addition to the debilitating symptoms caused by endometriosis, it is also a leading cause of female infertility.
What are heavy metals, and how do they affect our bodies?
According to the United Nations (UN) Environment Programme, heavy metals “normally occur in nature and are essential to life but can become toxic through accumulation in organisms.” The most common heavy metals are arsenic, cadmium, chromium, copper, nickel, lead and mercury. UNEP considers mercury, lead, and cadmium the most dangerous heavy metals because they can travel a long distance in the air.
Research on the effects of heavy metals in humans is increasing because, largely due to industrialization, the average person is potentially exposed to much higher levels than our foremothers were. Previously the industries with the highest heavy metal exposure were primarily populated by men, but now women are increasingly present in these same industries. Additionally, runoff from mining, chemical production, the transportation sector, and synthetic fertilizer production and use can increase the levels of heavy metals found in the natural environment, affecting men and women alike [1][4].
When present in the environment due to pollution from transportation, fertilizers, or power generation, heavy metals may enter the body when you breathe them in, ingest them in foods, or even absorb them into your skin. Infrequent exposure to these metals isn’t necessarily a health risk, but a steady exposure over time can cause these metals to build up in your system, causing oxidative stress in your body by increasing free radicals. These heavy metals are not only endocrine disruptors, but can also affect your nervous system and fertility. Toxic levels of heavy metals are known to cause organ damage, cancer, and infertility [1] [5].
Heavy metal exposure, infertility, and endometriosis: Is there a connection?
Drawing from the known adverse effects of heavy metal exposure on female fertility, a 2023 Chinese study published in the journal Science of the Total Environment asked whether there might also be a connection between heavy metal exposure and the development of endometriosis–a leading cause of female infertility. To investigate the possible connection, Chinese researchers studied blood levels and/or follicular fluid levels from 609 women seen at an IVF center [2]. Some of the women had both blood and follicular fluid tested, while others had one or the other. All samples were tested for concentrations of cadmium, mercury, arsenic, and lead.
The results suggested a strong link between heavy metal exposure and presence of endometriosis. Women with the highest blood levels of cadmium and lead (the study does not state the specific numbers) were three times more likely to have endometriosis compared to women with the lowest levels. Similarly, endometriosis was five times more common in women with the highest arsenic levels, and 13 times more common in women with the highest mercury levels.
Women with the highest blood levels of cadmium and lead were three times more likely to have endometriosis compared to women with the lowest levels. Similarly, endometriosis was five times more common in women with the highest arsenic levels, and 13 times more common in women with the highest mercury levels.
The follicular fluid data also demonstrated a connection: endometriosis was over two times more likely to be found in women with both the highest arsenic and mercury levels, and over three times more likely to be found in women with the highest cadmium levels, when compared to women with the lowest concentrations of those respective heavy metals in their follicular fluid samples.
The study controlled for factors like age, BMI, and hormone levels, and still displayed significant links between heavy metal exposure and rates of endometriosis. The study authors thus concluded that heavy metals both “individually and as a mixture, play a role in the risk of endometriosis” [2].
How might heavy metals increase endometriosis risk or worsen symptoms?
Lead, arsenic, cadmium, and mercury are specifically known to be endocrine disruptors, with wide-ranging effects on the reproductive system that include “menstrual disorders, adverse pregnancy outcomes, DNA damage and mitochondrial dysfunction, and higher breast and endometrial cancer risk.” It’s possible that heavy metals interact with estrogen receptors in the body to stimulate endometrial-like cell growth outside the uterus and overall worsen endometriosis symptoms, according to this analysis of the Chinese study.
However, not all research into the heavy metals/endometriosis question have found a definitive connection between the two. A 2021 systematic review (a review of previous studies to answer a very specific research question) found that data on whether heavy metal exposure triggers endometriosis was inconclusive.
Furthermore, in separate but related research, a 2019 study out of Turkey also aimed to find a connection between levels of heavy metals (in this case copper, zinc, aluminum, lead, and nickel) and women who suffered endometrial polyps (which many women with endometriosis also experience) [3]. Researchers analyzed the serum concentrations of these metals in 80 women, 40 with polyps and 40 without. This study did not find a direct increase in serum levels of any individual heavy metal for the 40 women who had polyps. While the heavy metals they studied did not appear to increase endometriosis rates on an individual basis, the study authors found some evidence that the ratio of one heavy metal to another may contribute to polyp risk. Might heavy metal ratios play a role in endometriosis risk as well?
What can be done?
In our modern day where pollution, waste disposal, fertilizers, and pesticides are dramatically increasing heavy metal concentrations in our environment, additional research is needed to establish whether and to what extent excess levels of heavy metals are contributing to the increase in endometriosis rates worldwide. According to these researchers, “stringent environmental regulations, sustainable practices, responsible waste management, research and innovation, public awareness, and collaboration between stakeholders” are all necessary to reduce heavy metals exposure. But as this study notes, “The use of mercury [as one example] has been greatly reduced in production activities and highly regulated in the fields where it is still permitted” [4]. For the average woman seeking to decrease her or her daughter’s risk of developing endometriosis, more on how to protect herself from environmental toxins is here and here.
References:
[1] Tchounwou PB, Yedjou CG, Patlolla AK, Sutton DJ. Heavy metal toxicity and the environment. Exp Suppl. 2012;101:133-64. doi: 10.1007/978-3-7643-8340-4_6. PMID: 22945569; PMCID: PMC4144270. [2] Shen, Lingchao et al. “The association between exposure to multiple toxic metals and the risk of endometriosis: Evidence from the results of blood and follicular fluid.” The Science of the total environment vol. 855 (2023): 158882. doi:10.1016/j.scitotenv.2022.158882 [3] Yılmaz, Betül Kalkan et al. “Serum concentrations of heavy metals in women with endometrial polyps.” Journal of obstetrics and gynaecology : the journal of the Institute of Obstetrics and Gynaecology vol. 40,4 (2020): 541-545. doi:10.1080/01443615.2019.1634022 [4] Caporossi, L.; Capanna, S.; Viganò, P.; Alteri, A.; Papaleo, B. From Environmental to Possible Occupational Exposure to Risk Factors: What Role Do They Play in the Etiology of Endometriosis? Int. J. Environ. Res. Public Health 2021, 18, 532. https://doi.org/10.3390/ijerph18020532 [5] Lin J, Lin X, Qiu J, You X, Xu J. Association between heavy metals exposure and infertility among American women aged 20-44 years: A cross-sectional analysis from 2013 to 2018 NHANES data. Front Public Health. 2023 Feb 14;11:1122183. doi: 10.3389/fpubh.2023.1122183. PMID: 36866101; PMCID: PMC9971928.
Great article, Madison. Do you know what other product we ingest has been found to have high levels of these same metals? Believe it or not, dark chocolate! Since it is rare to find a female who dislikes chocolate, especially dark due to its antioxidant heart health effects, I was quick to take note for our family’s chocolate fixes. It turns out California is the only state in our country that monitors these levels which is good because of all the chocolate producing companies located in CA. I learned Ghiradelli has the lowest levels. What’s interesting is why these levels may be high. It has to do with how the beans are processed after they are picked. The bean exposure to the elements as they are drying outdoors makes them like “magnets” for the metals in the swirling dirt that is airborne. Because our government (EPA) does not even monitor these levels, it has not been known until an independent lab conducted some tests. Anyway, thank you for this information.