L-shaped association of vitamin B1 with pelvic inflammatory disease: A cross-sectional study

Pelvic inflammatory disease (PID) is a common gynecological condition. While vitamin intake may influence PID risk, the role of vitamin B 1 remains unclear. This cross-sectional study explored the association between vitamin B 1 intake and PID risk. This study included data from the National Health and Nutrition Examination Survey 2013 to 2018. Weighted multivariate logistic regression, subgroup analyses, smooth curve fitting, and threshold effect modeling were applied in this study. A total of 3954 women aged 20 to 59 years were included. Tertile analysis confirmed a dose–response relationship: compared with the lowest tertile (Q1), both middle (Q2) and highest (Q3) tertiles showed reduced PID risk, with Q3 exhibiting the strongest protective effect (adjusted odds ratio [OR] = 0.631, P = .006). We identified an L-shaped association between vitamin B 1 and PID. A significant negative correlation was observed when vitamin B 1 intake was <1.938 (OR = 0.575, 95% confidence interval = 0.417–0.793, P < .001), whereas no statistically significant association was detected when intake exceeded 1.938 (OR = 1.370, 95% confidence interval = 0.769–2.440, P = .285). Subgroup analysis showed the association differed by hypertension, diabetes, and nonvigorous physical activity subgroups. The relationship between vitamin B 1 intake and PID conformed to an L-shaped curve (nonlinear, P = .009), with the inflection point measured at 1.938 mg/d, highlighting the close association between nutritional status and gynecological health. These results suggest that vitamin B 1 may correlate with a lower risk of PID. Further prospective studies are needed to explore the underlying mechanisms.