Approximately 14% of participants consumed ≥1 serving of diet soda daily (19.4% of whites, 8.6% of blacks, 11.9% of Hispanics, and 5.4% of Chinese), whereas 59% of participants reported never consuming diet soda. Fourteen percent consumed ≥1 serving of sugar-sweetened soda daily (10.7% of whites, 20.7% of blacks, 17.7% of Hispanics, and 3.4% of Chinese), whereas 45% never consumed sugar-sweetened soda. Twenty-four percent did not consume either beverage; only 2% reported consuming ≥1 serving of both at least daily. Over follow-up, 871 cases of incident metabolic syndrome (22.5%) and 413 cases of incident type 2 diabetes (8.2%) were identified. Demographic and lifestyle characteristics are shown in .
Characteristics of 5,011 participants free of prevalent type 2 diabetes according to diet soda consumption categories in MESA
Diet soda and risk of metabolic syndrome and type 2 diabetes
Compared with nonconsumers, the risk of metabolic syndrome was 36% greater in those consuming ≥1 serving of diet soda daily after adjustment for demographic characteristics and energy intake (model 2, ). Relative risk estimates changed little after additional adjustment for other dietary factors (foods or nutrients, data not shown). However, with adjustment for baseline measures of adiposity (waist circumference and/or BMI), the association was no longer significant (). Similarly, the association was strongly attenuated when adjusted for change in waist circumference or change in body weight between baseline and examination 4 (data not shown).
Risk of incident metabolic syndrome and type 2 diabetes according to diet soda consumption categories in participants from MESA
If we excluded from our analyses participants with any metabolic syndrome component at baseline (leaving a much smaller sample of 1,078 participants and 46 incident cases of metabolic syndrome), the HR comparing extreme diet soda consumption categories was greater (1.54 [95% CI 0.65–3.65], model 2) but not statistically significant.
Daily consumers of diet soda had a 67% elevated risk of type 2 diabetes compared with nonconsumers with adjustment for demographics and lifestyle factors (model 2, ). Adjustment for other dietary factors did not markedly change risk estimates (data not shown). With adjustment for baseline differences in waist circumference and/or BMI, HRs for type 2 diabetes were slightly attenuated but remained statistically significant (). The association also remained statistically significant with adjustment for change in waist circumference (HR 1.08 [95% CI 0.75–1.57], 1.45 [1.12–1.89], and 1.69 [1.28–2.22] across increasing diet soda consumption categories compared with nonconsumption, respectively). Results were similar when adjusted for change in body weight (data not shown).
With stratification for BMI (<25 vs. ≥25 kg/m2), HRs were similar in both strata for metabolic syndrome and type 2 diabetes, although there were few incident cases and much larger confidence intervals in the BMI <25 kg/m2 strata, comparing extreme intake categories for metabolic syndrome (HR 2.2 [95% CI 1.10–4.51] with BMI <25 kg/m2 and 1.48 [1.07–2.05] with BMI ≥25 kg/m2) and for type 2 diabetes (1.94 [0.87–4.35] with BMI <25 kg/m2 and 1.54 [1.15–2.07] with BMI ≥25 kg/m2).
Sugar-sweetened soda and risk of metabolic syndrome and type 2 diabetes
Although our primary analyses focused on diet soda intake, we also estimated corresponding risks for metabolic syndrome and type 2 diabetes according to consumption of sugar-sweetened soda. Data showed no significant associations between sugar-sweetened soda consumption and risk of either metabolic syndrome or type 2 diabetes (data not shown).
If risk estimates for type 2 diabetes across diet soda categories were calculated in only the participants who did not consume sugar-sweetened soda (n = 2,245), the association with diet soda consumption remained significant, although CIs were wide (HR 1.43 [0.79–2.61], 1.76 [1.18–2.63], and 2.23 [1.49–3.34], across increasing diet soda consumption categories compared with nonconsumption, respectively). This result was also true for metabolic syndrome (1.63 [1.13–2.36], 1.36 [1.02–1.81], and 1.81 [1.36- 2.42] across increasing diet soda consumption categories compared with nonconsumption, respectively, n = 1,773).
Metabolic syndrome component
Compared with nonconsumers, individuals consuming ≥1 daily serving of diet soda had a significantly greater risk of developing high waist circumference (≥102 cm if male and ≥88 cm if female) or high fasting glucose (≥100 mg/dl) during follow-up (HR 1.59 [95% CI 1.23–2.07] and 1.28 [1.08–1.52] for high waist circumference and high fasting glucose, respectively) (). Diet soda consumption was not associated with the development of other metabolic syndrome components (). As an alternative approach to address the same question, we also evaluated the amount of attenuation that occurred when metabolic syndrome HRs were adjusted for baseline measures of individual metabolic syndrome components. Similarly, the largest amount of attenuation occurred when HRs for incident metabolic syndrome were adjusted for baseline waist circumference or baseline fasting glucose concentration (comparing individuals consuming ≥1 serving of diet soda versus nonconsumers: 1.18 [0.96–1.44] adjusted for waist circumference; 1.23 [1.00–1.51] adjusted for glucose; 1.37 [1.12–1.68] adjusted for HDL cholesterol; 1.39 [1.14–1.70] adjusted for triglycerides; and 1.29 [1.06–1.58] adjusted for systolic and diastolic blood pressure).
Risk of developing metabolic syndrome components according to diet soda intake categories in participants from MESA
There were no significant interactions between diet soda or sugar-sweetened soda and age, sex, BMI, or waist circumference with respect to risk of metabolic syndrome, metabolic syndrome components, or type 2 diabetes. Results were also similar across race/ethnic strata. Furthermore, if Chinese were excluded from analyses (a group in which alternative metabolic syndrome criteria have been suggested), results were quite similar; i.e., greater diet soda intake remained associated with greater risk of type 2 diabetes and metabolic syndrome (data not shown).