Background: A gut-microbial metabolite, trimethylamine N-oxide (TMAO), has been associated with type 2 diabetes mellitus (T2DM). Few previous prospective studies have addressed associations between the changes in TMAO and T2DM incidence. Methods: Data were derived from a longitudinal cohort conducted from 2019 to 2021 in rural areas of Fuxin County, Liaoning Province, China, and 1515 diabetes-free participants aged above 35 years were included. The concentrations of serum TMAO and its precursors were measured at two time points, namely in 2019 and 2021. TMAO and TMAO changes (ΔTMAO) were separately tested in a logistic regression model. For further examination, the odds ratios (ORs) for T2DM were calculated according to a combination of TMAO levels and ΔTMAO levels. Results: During a median follow-up of 1.85 years, 81 incident cases of T2DM (5.35%) were identified. Baseline TMAO levels exhibited a nonlinear relationship, first decreasing and then increasing, and only at the highest quartile was it associated with the risk of T2DM. The OR for T2DM in the highest quartile of serum TMAO was 3.35 (95%CI: 1.55–7.26, p = 0.002), compared with the lowest quartile. As for its precursors, only choline level was associated with T2DM risk and the OR for T2DM in the Q3 and Q4 of serum choline was 3.37 (95%CI: 1.41–8.05, p = 0.006) and 4.72 (95%CI: 1.47–15.13, p = 0.009), respectively. When considering both baseline TMAO levels and ΔTMAO over time, participants with sustained high TMAO levels demonstrated a significantly increased risk of T2DM, with a multivariable-adjusted OR of 8.68 (95%CI: 1.97, 38.34). Conclusion: Both initial serum TMAO levels and long-term serum TMAO changes were collectively and significantly associated with the occurrence of subsequent T2DM events. Interventions aimed at normalizing TMAO levels, such as adopting a healthy dietary pattern, may be particularly beneficial in T2DM prevention.

Objectives: Gut microbiota-derived metabolites—trimethylamine N-oxide (TMAO) and its precursors choline, betaine, and carnitine—have been linked to various health outcomes. However, their role in gestational diabetes mellitus (GDM) remains unclear due to inconsistent findings. This study aims to investigate the associations between maternal plasma concentrations of these metabolites during early pregnancy and the risk of GDM. Methods: A nested case–control study was performed in the Shanghai Birth Cohort. GDM cases and non-GDM controls were matched according to maternal age at a ratio of 1:4. Three hundred twenty-one identified GDM cases and 1284 controls were included. Maternal plasma concentrations of TMAO and its precursors were measured between 12 and 16 weeks of gestation in early pregnancy using high-performance liquid chromatography-tandem mass spectrometry. Conditional logistic regression models were applied to assess associations between metabolite levels and GDM risk and to calculate odds ratios (ORs) and their 95% confidence intervals (CIs). Multivariate linear regressions evaluated relationships between metabolite concentrations and glycemic indicators. Stratified and sensitivity analyses were conducted to ensure robustness. Results: Maternal plasma levels of TMAO, choline, betaine, and carnitine in early pregnancy were 1.95 μmol/L (IQR, 1.16–3.20), 9.25 μmol/L (IQR, 7.31–11.98), 20.51 μmol/L (IQR, 16.92–24.79), and 17.13 μmol/L (IQR, 13.33–21.16), respectively. Betaine and carnitine were significantly higher in GDM cases (p = 0.002 and p = 0.042, respectively). No significant associations were identified between TMAO levels and GDM risk and glycemic indicators. Each SD increase in choline was associated with a 16% higher GDM risk (OR = 1.16, 95% CI: 1.01, 1.34, p = 0.039), while increased betaine and carnitine levels were linked to a 19% (OR = 0.81, 95% CI: 0.70, 0.95; p = 0.010) and 20% (OR = 0.80, 95% CI: 0.69, 0.94; p = 0.007) lower risk, respectively. Restricted cubic spline models showed no evidence of non-linear relationships (p_{for non-linearity} > 0.05). Interaction analyses indicated that the protective effect of betaine may be more pronounced in parous women. Conclusions: Higher early pregnancy levels of betaine and carnitine were associated with a reduced GDM risk, while elevated choline levels increased the risk. The protective association between betaine and GDM was more pronounced in parous women. No significant relationship was found between TMAO and GDM. The roles of choline, betaine, and carnitine in glucose metabolism warrant further investigation.

Natural polyamines, including spermidine (SPD), spermine (SPM) and putrescine (PUT), are evolutionarily conserved endogenous molecules crucially involved in central cellular processes. Their physiological importance may extend to the maintenance of cognitive function during aging. However, limited population-based epidemiological studies have explored the link between dietary polyamines and dementia risk. This study was a prospective analysis of 77,092 UK Biobank participants aged ≥ 60 years without dementia at baseline. We used Cox proportional hazard regression models to explore the associations between dietary polyamines and the risk of dementia, and restricted cubic splines to test the non-linear relationships. During a median follow-up of 12 years, 1087 incidents of all-cause dementia cases occurred, including 450 Alzheimer’s disease (AD) cases and 206 vascular dementia (VD) cases. The fully adjusted hazard ratios (HRs) for the upper fourth quintile of dietary SPD, in comparison with the lowest quintile of intake, were 0.68 (95% confidence interval [95% CI]: 0.66–0.83) for the risk of all-cause dementia, 0.62 (95% CI: 0.45–0.85) for AD and 0.56 (95% CI: 0.36–0.88) for VD, respectively. A 26% reduction in dementia risk [HR: 0.74, (95% CI: 0.61–0.89)] and a 47% reduction in AD [HR: 0.53, (95%CI: 0.39–0.72)] were observed comparing the third with the lowest quintiles of dietary SPM. Dietary PUT was only associated with a reduced risk of all-cause dementia in the fourth quintile [HR (95% CI): 0.82 (0.68–0.99)]. Reduced risk was not found to be significant across all quintiles. There were ‘U’-shaped relationships found between dietary polyamines and all-cause dementia, AD and VD. Stratification by genetic predisposition showed no significant effect modification. Optimal intake of polyamines was linked to a decreased risk of dementia, with no modification by genetic risk. This potentially suggests cognitive benefits of dietary natural polyamines in humans.

This study investigated the relationship between trimethylamine N-oxide (TMAO), its precursors (choline, betaine, and carnitine), and the prevalence of hypertension in rural northeastern China. Conducted in 2019, the cross-sectional study involved 1,899 adults aged 35 and older, with serum levels of TMAO and its precursors quantified using high-performance liquid chromatography-mass spectrometry. Hypertension was defined according to blood pressure measurements or the use of antihypertensive medications, based on the 2018 Chinese Hypertension Guidelines. Logistic regression models were utilized to assess the associations between TMAO, its precursors, and hypertension, adjusting for potential confounders such as age, sex, smoking status, and physical activity. The results revealed a significant association between TMAO concentrations and the prevalence of hypertension. Participants in the highest quartile of TMAO (>7.75 μmol/L) exhibited a 36 % increased risk of hypertension (OR = 1.360, 95 % CI: 1.043-1.772, P = 0.023). Choline also showed a positive association with hypertension (OR = 1.426, 95 % CI: 1.092-1.863, P = 0.009), while no significant association was found for betaine. Conversely, carnitine was negatively associated with hypertension risk in the highest quartile. Subgroup analyses indicated that these associations varied by age, gender, and education level. Elevated serum levels of TMAO and choline were associated with an increased risk of hypertension. Modulating TMAO metabolism could aid in the prevention of hypertension in the future.