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

Figures & data

Table 1 Baseline Characteristics of Study Variables by Tertiles of Cumulative Tryptophan Intake in the CHNS, 1997–2011

Baseline Variable	Overall Participants	Tertiles of Dietary Tryptophan Intake			P-Value
		T1 (n=2624)	T2 (n=2636)	T3 (n=2630)
Baseline tryptophan consumption (mg/g protein)	13.45 (1.04)	12.29 (0.52)	13.49 (0.25)	14.56 (0.56)	<0.001
MetSyn cases, n (%)	1290 (16.3)	527 (20.1)	457 (17.3)	306 (11.6)	<0.001
Age (years)	43.43 (14.85)	43.82 (14.60)	43.15 (14.77)	43.32 (15.18)	0.23
Female, n (%)	3951 (50.1)	1290 (49.2)	1334 (50.6)	1327 (50.5)	0.52
BMI (kg/m^2)	22.27 (2.89)	22.81 (2.96)	22.33 (2.93)	21.66 (2.66)	<0.001
Waist (cm)	77.38 (8.61)	79.04 (8.86)	77.59 (8.60)	75.51 (8.00)	<0.001
WHR	0.85 (0.063)	0.85 (0.065)	0.85 (0.061)	0.84 (0.061)	<0.001
PAL (MET-h/week)	308.96 (182.85)	306.28 (186.00)	305.71 (183.87)	314.90 (178.52)	0.12
Energy intake (kcal/day)	2232.52 (663.44)	2406.32 (728.30)	2279.18 (631.69)	2312.37 (618.83)	<0.001
Protein intake (g/day)	68.99 (22.37)	75.86 (24.45)	67.99 (21.01)	63.14 (19.51)	<0.001
Fat intake (g/day)	65.54 (35.89)	64.87 (37.47)	71.46 (36.82)	60.26 (32.28)	<0.001
Carbohydrate intake (g/day)	363.64 (126.09)	376.97 (142.76)	337.91 (113.61)	376.13 (115.92)	<0.001
SBP (mmHg)	118.63 (17.72)	120.85 (17.8)	118.30 (17.87)	116.79 (17.25)	<0.001
DBP (mmHg)	77.03 (10.85)	78.25 (10.74)	77.02 (11.26)	75.84 (10.39)	<0.001
Living in city, n (%)	2273 (28.8)	759 (28.9)	936 (35.5)	578 (22.0)	<0.001
Urban index	51.92 (2.77)	51.95 (2.96)	52.03 (2.73)	51.79 (2.62)	0.005
High school education, n (%)	1369 (17.4)	454 (17.3)	568 (21.5)	347 (13.2)	<0.001
Smoking, n (%)	2627 (33.3)	885 (33.7)	889 (33.7)	853 (32.4)	0.52
Drinking, n (%)	2903 (36.8)	1006 (38.3)	994 (37.7)	903 (34.3)	0.005
Sleep time (h)	8.13 (1.16)	8.08 (1.13)	8.10 (1.18)	8.21 (1.16)	<0.001
Prevalent diabetes, n (%)	101 (1.3)	23 (0.9)	32 (1.0)	46 (1.7)	0.018
Prevalent obesity, n (%)	344 (4.4)	162 (6.2)	114 (4.4)	69 (2.2)	<0.001
Prevalent overweight/obesity, n (%)	1273 (16.1)	534 (20.4)	467 (17.7)	272 (10.3)	<0.001
Prevalent hypertension, n (%)	1409 (17.9)	548 (20.9)	473 (17.9)	388 (14.8)	<0.001

Notes: Continuous data are expressed as mean (SD) or number (%); generalized linear models and χ² test were used to probe for differences in continuous variables and dichotomous variables.

Abbreviations: MetSyn, metabolic syndrome; BMI, body mass index; WHR, waist-to-hip ratio; PAL, physical activity level; SBP, systolic blood pressure; DBP, diastolic blood pressure.

Table 2 Associations Between the Cumulative Consumption of Dietary Tryptophan and the Risk of MetSyn, from Cox Proportional Hazards Models, CHNS, 1997–2011

	Tertiles of Cumulative Dietary Tryptophan Intake			P for Trend	Per 1 mg/g Protein Increment	P-Value
	T1	T2	T3
Cases, n (%)	527 (20.1)	457 (17.3)	306 (11.6)		1290 (16.3)
Model 1
HR (95% CI)		0.88 (0.77–0.99)	0.63 (0.55–0.72)	<0.001	0.84 (0.80–0.89)	<0.001
Model 2
HR (95% CI)	1	0.88 (0.78–1.00)	0.63 (0.54–0.72)	<0.001	0.84 (0.80–0.89)	<0.001
Model 3
HR (95% CI)	1	0.98 (0.86–1.11)	0.78 (0.68–0.90)	0.001	0.92 (0.87–0.97)	0.004
Model 4
HR (95% CI)	1	0.98 (0.86–1.11)	0.78 (0.68–0.90)	0.001	0.92 (0.87–0.97)	0.003
Model 5
HR (95% CI)	1	0.99 (0.87–1.12)	0.79 (0.69–0.91)	0.002	0.92 (0.87–0.98)	0.004
Model 6
HR (95% CI)	1	0.99 (0.87–1.15)	0.77 (0.65–0.90)	0.003	0.91 (0.86–0.97)	0.005

Notes: Model 1 was the crude Cox proportional hazards models without adjusting for any covariate; Model 2 was further adjusted for age and sex; Model 3 was further adjusted for WHR and BMI; Model 4 was further adjusted for smoking and drinking status; Model 5 was further adjusted for living site, physical activity, urban index, cardiovascular disease, and energy intake; Model 6 was adjusted for all variables in model 5, with further adjustment for AHEI, SFA, fiber, sugar, fruit, and vegetable intake.

Abbreviations: MetSyn, metabolic syndrome; WHR, waist-to-hip ratio; BMI, body mass index; AHEI, Alternate Healthy Eating Index; SFA, saturated fatty acid.

Table 3 Differences in Sleep Time and Blood Biochemical Factors Across Cumulative Dietary Tryptophan Intake

	Dietary Tryptophan Intake in Tertiles					Dietary Tryptophan Intake in Continuous Form
	T1	T2	T3	Effect Size	P for Trend	Effect Size	P-Value
Sleep time (h)	8.10 (0.027)	8.12 (0.025)	8.19 (0.027)	0.042 (0.020)	0.033	0.055(0.016)	0.001
FPG (mmol/L)	5.58 (0.040)	5.38 (0.038)	5.39 (0.042)	−0.091 (0.030)	0.003	−0.097 (0.021)	<0.001
HbA1c (%)	5.86 (0.026)	5.56 (0.025)	5.56 (0.027)	−0.148 (0.020)	<0.001	−0.152(0.016)	<0.001
TC (mmol/L)	4.98 (0.027)	4.92 (0.026)	4.84 (0.028)	−0.072 (0.021)	<0.001	−0.063(0.017)	<0.001
LDL-C (mmol/L)	3.11 (0.026)	2.99 (0.025)	2.95 (0.028)	−0.081 (0.020)	<0.001	−0.071(0.016)	<0.001
APO-B (g/L)	0.93 (0.007)	0.89 (0.007)	0.88 (0.007)	−0.021 (0.005)	<0.001	−0.018(0.004)	<0.001

Notes: Multivariable generalized linear models were used to probe for differences across tertiles of tryptophan consumption with adjustment for sex, age, BMI, WHR, smoking status, drinking status, living site, physical activity, urban index, cardiovascular disease, AHEI, SFA, fiber, sugar, fruit, vegetable, and energy intake. Multivariable linear regression models were used to calculate the effect sizes per 1 mg/g protein increment of tryptophan, adjusting for the same variables. Data are mean (SD).

Abbreviations: FPG, fasting plasma glucose; HbA_1c, glycosylated hemoglobin; TC, total cholesterol; LDL-C, low-density lipoprotein cholesterol; APO-B, apolipoprotein B; BMI, body mass index; WHR, waist-to-hip ratio; AHEI, Alternate Healthy Eating Index; SFA, saturated fatty acid.

Figure 1 Mediation effect of sleep time between cumulative dietary tryptophan intake and risk of MetSyn in the CHNS, 1997–2011.

Notes: Data are standardized regression coefficients with adjustment for sex, age, BMI, WHR, smoking status, drinking status, living site, physical activity, urban index, cardiovascular disease, AHEI, SFA, fiber, sugar, fruit, vegetable, and energy intake. *P<0.05 for coefficients different from 0.

Abbreviations: MetSyn, metabolic syndrome; BMI, body mass index; WHR, waist-to-hip ratio; AHEI, Alternate Healthy Eating Index; SFA, saturated fatty acid.