Compositive Dietary Antioxidant Index Linked to endometriosis-related RA

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A new study highlights the importance of daily antioxidant intake for endometriosis-related RA.

A new study found a lower Compositive Dietary Antioxidant Index (CDAI) is linked to the risk of endometriosis-related rheumatoid arthritis (RA).1

“In the present study, the presence of EM was associated with the risk of RA, which was supported by the previous studies,” wrote investigators, led by Haiyang Hu, from the department of gynecology at Affiliated Hospital of Jining Medical University in Shandong, China

Previous research found patients with endometriosis are nearly 4 times as likely to develop RA than those without endometriosis.2 RA puts a burden on patients, from pain and disability to premature mortality, associated comorbidities, reduced quality of life, and increased medical expenses.1

Due to the high burden, determining the factors linked to endometriosis-related RA is important in managing the inflammatory joint disease. Investigators sought to evaluate the link between the Compositive Dietary Antioxidant Index and the risk of endometriosis-related RA in women of childbearing age. The team conducted a cross-sectional study to assess this association and leveraged data from the National Health and Nutrition Examination Survey database spanning 1999 – 2006.

Participants were included if they were women of childbearing age (20 – 44 years old), had assessments of endometriosis and RA, and a complete dietary intake information in the NHANES database. They were excluded if they had extremely low or high total energy intake (< 500 kcal/day or >5000 kcal/day) or had missing information on key covariates.

Investigators determined the CDAI of participants by summing the standardized Z-values of 6 dietary antioxidant micronutrients: vitamin A, vitamin C, vitamin E, zinc, magnesium, and selenium. From there, participants were grouped according to the median Q2 -0.65: < Q2 (lower-level intake) and ≥ Q2 (higher-level intake). Both endometriosis and RA data were obtained on a questionnaire-based survey.

The team used weighted logistic analysis to determine the associations of CDAI and endometriosis with the risk of RA. Furthermore, addictive interaction was assessed using the relative excess risk due to interaction (RERI), the attributable proportion due to interaction, and the synergy index.

The study included 3803 patients, and 74 (1.99%) had RA. Of the sample, 65.78% were White, 12.36% were Black, and 21.89% were from other racial groups. The mean age of the sample was 31.68 years old.

Hu and colleagues found a lower CDAI (odds ratio [OR], 1.85; 95% confidence interval [CI], 1.12 to 3.04, P = .015) and the presence of endometriosis (OR, 3.05; 95% CI, 1.19 to 7.81, P = .023) was linked to the risk of RA.

An addictive interaction existed between a lower CDAI and the presence of EM on the risk of RA (OR, 6.19; 95% CI, 2.33 to 16.43; P < .001, P of trend = .007). However, no significant interaction was observed after being assessed by relative excess risk due to interaction, the attributable proportion due to interaction, and the synergy index. Investigators did find a significant effect of a lower CDAI and endometriosis on the risk of RA (OR, 3.94; 95% CI, 1.35 to 11.51; P = .013).

Investigators noted a few limitations, such as the cross-sectional design not allowing to determine causality, questionnaires leaving room for bias, and not being able to assess the potential influence of participants changing parts of their lifestyle such as their diet.

“This study elucidates the importance of daily antioxidant intake for [endometriosis]-related RA,” investigators concluded.


  1. Hu H, Wang X, Ren Y, Zhang T, Sun L. Association Between Composite Dietary Antioxidant Index and the Risk of Endometriosis-Related Rheumatoid Arthritis in Women of Childbearing Age: A Cross-Sectional Study Based on the National Health and Nutrition Examination Survey Database. Int J Womens Health. 2024;16:717-726. Published 2024 Apr 23. doi:10.2147/IJWH.S453602
  2. Kronemyer, B. Risk of Rheumatoid Arthritis With Endometriosis. Contemporary OB/GYN. February 17, 2022. Accessed May 2, 2024.