Dietary Tryptophan and the Risk of Metabolic Syndrome: Total Effect and Mediation Effect of Sleep Duration

PURPOSE: Tryptophan affects energy homeostasis, glucose metabolism, blood pressure, and sleep. However, studies investigating the association between tryptophan and metabolic syndrome (MetSyn) are rare. We aimed to investigate the associations of dietary tryptophan with MetSyn incidence and potential mediation via sleep duration. METHODS: Data of 7890 participants were obtained from the China Health and Nutrition Survey (1997–2011) (male: 49.9%; mean age=43.43 years;median follow-up=129.76 months; MetSyn incidence: 16.3%). A combination of individual 24-hour recall and household survey was used to assess dietary intake. In total, 6720 and 4474 participants who reported sleep duration and had blood samples taken, respectively, were incorporated into subgroup analyses. MetSyn was defined according to National Cholesterol Education Program Adult Treatment Panel (NCEP ATP) III criteria (2004), and tryptophan consumption and sleep duration were assessed by self-report in each survey. Multivariate Cox regression models were used to assess the associations between tertiles of tryptophan intake and MetSyn. Generalized linear regression models were used to evaluate the effect of tryptophan on sleep duration and plasma biomarkers. RESULTS: Dietary tryptophan showed a protective effect on the risk of MetSyn. The hazard ratio (95% CI) of MetSyn was 0.77 (0.65–0.90) for individuals with a high tertile of tryptophan. Sleep duration was significantly higher, and HbA(1c), total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and apolipoprotein B (APO-B) were lower in the high tertile of tryptophan compared to the low tertile (P<0.05). In addition, mediation effects on the association between tryptophan intake and MetSyn risk were observed for sleep duration (estimated mediation percentage: 26.5%). CONCLUSION: Our study demonstrated a negative association between dietary tryptophan and MetSyn incidence, and the mediation effect of sleep duration on this association, after adjusting for numerous confounders such as nutrients and food patterns. These findings may have important public health implications for the improvement of cardiometabolic health.