Association between mixed dietary B vitamin intake and insulin resistance in US middle-aged and older adults without diabetes: The Bayesian kernel machine regression approach

Background and Objectives: In daily life, the intake of dietary nutrients is mixed. However, evidence for the as-sociation between mixed dietary B vitamin intake and insulin resistance is limited. In this study, we estimated the joint effect of intake of various dietary B vitamins on insulin resistance. Methods and Study Design: This cross-sectional study used data from the National Health and Nutrition Examination Survey 2011-2018. We included 1,628 middle-aged and 1,058 older adults without diabetes. Multivariable logistic regression and Bayesian kernel machine regression models were constructed. Results: In the multivariable logistic regression, when all B vita-mins were included in the model, the ORs (95% CIs) of insulin resistance were 3.06 (1.00-9.37) and 0.42 (0.19-0.93) for the highest quartile of vitamin B-1 and B-12 intake in the middle-aged group when the lowest quartile was the reference. In the older group, no significant association was observed. In the Bayesian kernel machine re-gression analysis, a negative trend was noted between mixed B vitamin intake and insulin resistance in both ex-amined groups. The univariate exposure-response function indicated that vitamin B-12 intake was negatively as-sociated with insulin resistance in the middle-aged group, and that vitamin B-6 and dietary folate equivalent in-takes were negatively associated with insulin resistance in older group. The bivariate exposure-response function indicated a potential interaction effect between dietary intake of vitamin B-12 and those of vitamin B-1, B-2, nia-cin, and dietary folate equivalent on insulin resistance in older people. Conclusions: Our results suggest that mixed dietary B vitamin intake tends to decrease the OR of insulin resistance both in middle-aged and older peo-ple.