Jun Liang,1 Jie Hao,2 Yu Qin,1 Ou Liu,1 Kunning Shao,1 Wei Zhao,1 Jiangping Wen1 

1Department of Laboratory, The First Hospital of Tsinghua University, Beijing, People’s Republic of China; 2Beijing Tongren Eye Center, Beijing Tongren Hospital, Capital Medical University, Beijing Ophthalmology and Visual Science Key Laboratory, Beijing, People’s Republic of China

Correspondence: Jiangping Wen, Email wenjiangping1224@126.com

Background: Conflicting evidence exists regarding the association of gut microbiota-related metabolites – TMAO and its precursor choline and betaine with type 2 diabetes Mellitus (T2DM), particularly in rural Chinese populations. This study aimed to prospectively examine these relationships in a northern rural Chinese cohort.
Methods: A nested case–control study was conducted within the Handan Eye Study. At baseline (2006– 2007), 5,512 participants aged ≥ 30 years were enrolled. After 6.5 years of follow-up, 209 incident T2DM cases and 394 age- and sex-matched controls were included. Plasma choline, betaine, and TMAO levels were measured using ultra-performance liquid chromatography. Logistic regression and linear models assessed associations with T2DM risk, insulin resistance (IR), and metabolic parameters.
Results: Baseline betaine level was lower in the T2DM group compared to controls (betaine: 7431.4 ng/mL versus 7821.5 ng/mL). After adjusting for BMI, waist-to-hip ratio, and diabetes history, no significant associations were found between choline, betaine, or TMAO and T2DM risk. However, higher betaine quartiles showed a trend toward reduced T2DM risk (Q4 vs Q1 OR: 0.59, 95% CI: 0.34– 1.06). Betaine was inversely correlated with HOMA-IR (β = − 0.16), HOMA-β (β = − 0.13), and TyG index (β = − 0.21) (p < 0.05). Plasma choline levels were positively associated with fruit intake frequency, while TMAO levels decreased with higher exercise intensity.
Conclusion: Betaine may play a protective role against dyslipidemia, adiposity, and T2DM risk in rural Chinese populations. Further studies are needed to explore TMAO’s complex role in diabetes development.

Keywords: type 2 diabetes, choline, betaine, TMAO, nested case–control study