Association of composite dietary antioxidant index with menopause age and reproductive lifespan in NHANES 1999–2018: A Cross-Sectional study

Accumulated evidence has shown that the antioxidant diet exhibits protective effects on women's reproductive health. The Composite Dietary Antioxidant Index (CDAI) serves as a crucial indicator for assessing antioxidant-rich diets. However, the relationship between CDAI and menopause age as well as reproductive lifespan remains unclear. In this cross-sectional analysis, we investigated these associations using data from 4514 post-menopausal women who participated in the National Health and Nutrition Examination Survey (NHANES) from 1999 to 2018. Analyses incorporated sampling weights and design variables to address its complex survey structure, ensuring nationally representative results Information on age at menopause and reproductive lifespan was derived from questionnaire data. The CDAI was calculated based on the intake of selenium, zinc, carotenoid, Vitamin A, C and E. Multiple linear regression, smooth curve fitting, threshold effect analysis, and subgroup analysis were used to investigate the association between the CDAI and age at menopause as well as reproductive lifespan. After adjusting for age, race, BMI and other confounding factors, our findings revealed that higher CDAI was associated with a later age at menopause (β = 0.09, 95% CI = 0.02-0.15, P = 0.013) and longer reproductive lifespan (β = 0.11, 95% CI = 0.04-0.18, P = 0.001). A nonlinear threshold effect was identified, with an inflection point at CDAI = 1.05. Below this threshold, each unit increase in CDAI was associated with a 0.24-year delay in menopause (β = 0.24, 95% CI = 0.09-0.39, P = 0.002), but this effect was not observed above this point. Additionally, each standard deviation increase in CDAI was associated with a 4% decrease in early menopause risk (OR = 0.96, 95% CI = 0.92-1.00, P = 0.048). The use of oral contraceptives and female hormones modified these relationships. Our research highlighted a positive non-linear association between CDAI and age at menopause, as well as reproductive lifespan, emphasizing the potential clinical relevance of dietary antioxidant optimization within specific thresholds.