Higher zinc intake linked to increased endometriosis risk, study finds

New research uncovers a surprising link between dietary zinc and endometriosis, raising questions about zinc’s role in women’s health and its potential influence on this painful, chronic condition.

Study: Exploring the link between dietary zinc intake and endometriosis risk: insights from a cross-sectional analysis of American women. Image Credit: Shutterstock AI / Shutterstock.com

In a recent study published in BMC Public Health, researchers explore the association between zinc intake and endometriosis risk.

What is endometriosis?

Endometriosis is defined as the presence of endometrium-like tissue outside the uterus, where it forms the internal lining. This painful condition, which often affects pelvic organs and tissues, can lead to severe complications including intra-abdominal adhesions, infertility, and ectopic pregnancy.

Current estimates indicate that about 176 million women throughout the world are living with endometriosis. Some of the different factors that increase the risk of endometriosis include dysmenorrhea, subfertility, and pelvic pain by 40-60%, 21-47%, and 71-87%, respectively.

The origin of endometriosis remains unclear; however, research indicates that genetic, inflammatory, immune, and environmental factors are involved.

About zinc

Many physiological processes require zinc, a trace element that is central to DNA synthesis, gene transcription, and cell division, all of which are fundamental to human reproduction.

Zinc cannot be stored; therefore, dietary intake through the consumption of meat, grains, and dairy is crucial to prevent deficiency in this element. The mean daily intake of zinc varies, ranging from 4.6-6.2 mg/day in children under three years of age to eight to 14 mg/day in adults.  

Zinc deficiency is associated with altered immune cell counts and function, thereby increasing the risk of cancer, autoimmune disease, infectious disease, as well as altered female ovarian development and function. Conversely, excessive zinc intake can lead to immunosuppression.

In endometriosis, zinc regulates immunologic pathways and oxidative stress while also controlling the activity of matrix metalloproteinases (MMPs) that are involved in tissue remodeling during maturation or after injury. MMP activity may be involved in the invasive behavior of endometriotic tissue, as these enzymes degrade the extracellular matrix.

About the study

Data for the current study were obtained from the National Health and Nutrition Examination Survey conducted between 1999 and 2006 among American women between 20 and 54 years of age. A total of 4,315 women were included in the current study, 7.7% of whom reported a diagnosis of endometriosis.

About 64% of women were overweight, 39.4% were smokers, and 47% were taking dietary supplements. Over 53% and 14% of the study cohort were below 40 years and above 50 years, respectively.

Increased dietary zinc intake was correlated to the use of dietary supplements, moderate exercise, living with a partner, and higher income. Zinc content in the diet was associated with an increased risk of endometriosis, even after compensating for these confounding factors.

As compared to those who consumed eight mg of zinc or less every day, the risk of endometriosis was 60% higher among those whose diet supplied over 14 mg/day of zinc. No significant change in the risk of endometriosis was observed among those who consumed between eight and 14 mg/day of zinc.

Further analysis showed that the correlation between increased zinc intake with endometriosis risk was independent of lifestyle or demographic factors like smoking, obesity, or race.

Previous studies have reported lower zinc levels present in women with endometriosis. The study findings contradict these results, which may be attributed to different zinc profiles in plasma as compared to urine, or because earlier studies included smaller patient cohorts.

How does zinc affect endometriosis risk?

Several studies have demonstrated that women diagnosed with endometriosis exhibit higher levels of MMP-2 and MMP-9 as compared to controls. MMPs breakdown the extracellular matrix, which subsequently leads to the release various bioactive molecules including cytokines, chemokines, cell adhesion molecules, growth factors, and bioactive peptides. Furthermore, by metabolizing the ECM, MMPs facilitate the penetration of endometrial cells into surrounding tissues.

The levels of metallothionen, a protein that binds to zinc following dietary absorption, often increase as individuals age and in the presence of inflammation. Thus, the continuous sequestration of zinc by metallothionein reduces the availability of zinc as an enzyme cofactor and MMP inhibitor. High levels of zinc in the body may also promote pathogen multiplication by causing immunosuppression.

Zinc may also be a metalloestrogen, which is defined as a metal ion that activates estrogen receptors. In this context, zinc may promote endometriosis, which is an estrogen-dependent condition.

Conclusions

The study findings suggest that increased dietary zinc is associated with a higher risk of endometriosis. However, further research is needed to elucidate the mechanisms involved in this association and clarify whether zinc intake is a modifiable risk factor in women’s health.