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Nonlinear association between composite dietary antioxidant index and irritable bowel syndrome: insights from UK
Laifu Li1,2, Yan Zhuang1,2, Yan Ran1,2
1Department of Gastroenterology, Second Affiliated Hospital of Xi'an Jiaotong University, Xi'an, China.
Background:
The relationship between overall dietary antioxidant potential and risk of irritable bowel syndrome (IBS) is unclear and needs further epidemiologic evidence.
Methods:
In this study, we included a total of 157,900 participants from the UK Biobank without irritable bowel syndrome at baseline between 2006 and 2010. Dietary intake was assessed using the online 24-hour dietary recall questionnaire, Oxford WebQ. IBS was identified using the ICD-10 code (K58). The composite dietary antioxidant index (CDAI) was the sum of Z scores for mean intake of individual vitamins A, C, E, manganese, selenium, and zinc from five 24-hour dietary recalls.
Results:
During a mean follow-up time of 13.41 years, 2,007 incident cases of IBS were identified among the 157,900 participants. Restricted cubic spline (RCS) showed a nonlinear association (p for nonlinear < 0.001) between CDAI and the risk of IBS, and two-piecewise linear regression identified an inflection point at -0.9. Segmented Cox regression demonstrated that increasing CDAI significantly reduced the risk of IBS when CDAI < -0.9 (HR: 0.900, 95% CI: 0.820-0.988, P = 0.027); however, when CDAI ≥ -0.9, there was a 3% increased risk of IBS (HR: 1.030, 95% CI: 1.001-1.060, P = 0.046). Furthermore, compared to participants in Quintile 2 of CDAI, individuals in Quintile 1 had a 23% increased risk of IBS (HR: 1.228, 95% CI: 1.071-1.408, P = 0.003), while no significant differences were observed for participants in the other quintiles. Nonlinear analysis of independent dietary nutrients suggested a significant U-shaped association only between vitamin C and the risk of IBS, with an inflection point at Z score = -0.1. Sensitivity analyses with multiple imputation for missing covariates supported a negative association between antioxidant intake and IBS risk before the inflection point of CDAI. In contrast, after the inflection point, CDAI seemed to be unrelated to IBS risk.
Conclusion:
Moderate supplementation of antioxidants, particularly vitamin C, is beneficial in reducing the risk of IBS. However, excessive intake of dietary antioxidants tends to have no protective effect on IBS risk.
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