A Positive Relationship Between Caffeine Intake and Endometriosis: A Cross-Sectional Study of the National Health and Nutrition Examination Survey 1999-2006.

BACKGROUND

Caffeine has been suggested to have a relationship with endometriosis as a widely consumed psychoactive substance, although findings are inconsistent.

OBJECTIVE

This study explored the potential associations and threshold effects between caffeine intake and endometriosis using cross-sectional data from the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2006.

METHODS

The study included 248 women with endometriosis and 2944 without, aged 20-50 years. Caffeine intake was assessed through a 24-h dietary recall, and endometriosis was identified via self-report. Logistic regression models were used to investigate the associations between caffeine intake and endometriosis, adjusting for age, race, body mass index, marital status, education, ever pregnant, smoke, drink, hypertension, hyperlipidemia, diabetes, energy, protein, total fat and dietary fibre. The restricted cubic spline (RCS) regression was employed to examine nonlinear relationships and threshold effects.

RESULTS

This study found a significant correlation between endometriosis and caffeine intake, with both high and low levels associated with the condition (OR 1.65, 95% CI: 1.12, 2.42, p = 0.011 for high; OR 1.60, 95% CI: 1.05, 2.44, p = 0.028 for low). Their relationship is still significant after adjustment for covariates. This suggests a complex dose-response relationship, confirmed by RCS regression, which revealed a U-shaped curve. Endometriosis incidence was lowest at 170.25 mg/day caffeine intake.

CONCLUSION

The research suggests that an optimal caffeine intake is 170.25 mg/day, with both higher and lower levels associated with endometriosis. We acknowledge that the cross-sectional design limits causal inference and that reliance on self-reported data may introduce bias. Nevertheless, our findings lay the groundwork for future investigations into the dose-response relationship between caffeine intake and endometriosis.