Dhingra et al
All analyses were performed with SAS software version 9.0 (SAS Institute, Cary, NC). A 2-sided probability value of 0.05 was considered statistically significant.
The authors had full access to and take full responsibility for the integrity of the data. All authors have read and agree to the manuscript as written.
Results The baseline characteristics of participants according to the categories of soft drinks consumed per day are presented in Table 1. Approximately 35% of the participants reported consuming 1 soft drink per day in response to the exami- nation cola questionnaire (data based on all 3 examinations). In comparison, only 22% of participants reported intake of at least 1 soft drink (diet or regular) per day in response to the FFQ (data available for examinations 5 and 6 only). The lower proportion reporting daily intake on the FFQ may be related to the greater number of options available to indicate soft drink intake; participants drinking 1 to 6 soft drinks per week (also 22% on the FFQ) may have rounded their responses on the examination cola questionnaire to the nearest integer.
In age- and sex-adjusted models, the prevalence of obesity (assessed both by body mass index and by waist circumfer- ence), high blood pressure, glucose intolerance, low HDL-C, and hypertriglyceridemia was significantly higher in those who consumed a greater number of soft drinks per day. Serum total cholesterol, low-density lipoprotein cholesterol, physical activity index, and alcohol consumption did not vary across categories of soft drinks consumed. Similar trends were obtained when we excluded individuals with prevalent metabolic syndrome (Data Supplement, Table I).
Prevalence of the Metabolic Syndrome There was a 48% higher adjusted prevalence of metabolic syndrome among those who consumed 1 or more soft drinks per day relative to individuals with infrequent soft drink consumption (Table 2). We observed a rising prevalence of metabolic syndrome across categories of 1 and 2 soft drinks per day. In parallel analyses with the data from the FFQ (Table 2), participants who consumed 1 diet or regular soft drink per day had nearly a 1.8-fold adjusted prevalence of metabolic syndrome compared with infrequent drinkers (1 per week).
Incidence of the Metabolic Syndrome Individuals who consumed at least 1 soft drink per day had a 44% higher adjusted risk (95% CI, 20% to 74%) of develop- ing metabolic syndrome compared with infrequent drinkers in multivariable-adjusted analyses (Table 3). There was no effect modification by age, body mass index, or sex (interac- tion terms were not statistically significant). After additional adjustment for baseline levels of covariates (blood sugar, systolic and diastolic blood pressure, triglycerides, and HDL-C) and alcohol consumption in our models, the associ- ation of consumption of 1 soft drink per day with incidence of metabolic syndrome remained robust (odds ratio [OR], 1.44; 95% CI, 1.19 to 1.74). Further exclusion of individuals with diabetes mellitus at baseline (n138) attenuated the association (OR for 1 soft drink per day, 1.16; 95% CI 1.00
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Soft Drink Consumption and Metabolic Risk
to 1.34). After stratification of analyses by caffeinated versus decaffeinated drinks, results were consistent with the primary analyses; consumption of 1 soft drink per day was associ- ated with incident metabolic syndrome for both types of beverages (Data Supplement, Table II).
In analyses with FFQ data (Table 3), intake of at least 1 regular or diet soft drink per day was associated with a 50% higher incidence of metabolic syndrome than among those who drank 1 soft drink per week, although the association was borderline significant for intake of 1 regular soft drink per day (P0.07). We also observed a graded increase in the risk of metabolic syndrome from those who were consuming 1 to 6 diet or regular soft drinks per week to those who drank
1 soft drinks per day (diet or regular).
Incidence of Individual Components of the Metabolic Syndrome Compared with infrequent drinkers, individuals who con- sumed 1 soft drink per day had a 25% to 32% higher adjusted risk of incidence of each individual metabolic trait (Table 4), with the exception of development of high blood pressure, for which there was a borderline significant 18% higher adjusted odds (P0.10).
Discussion In the present study, we observed a significantly higher prevalence of metabolic syndrome among middle-aged adults who consumed 1 soft drink per day. This association was consistent for intake of both regular and diet soft drinks. Our prospective analyses corroborated the cross-sectional find- ings; we observed an increase in the incidence of metabolic syndrome among adults consuming at least 1 soft drink per day, regardless of whether it was of the regular or diet type. Additionally, consumption of soft drinks daily was associated with a higher incidence of each metabolic syndrome compo- nent. The present study extends results from prior studies that reported that a greater intake of soft drinks is associated with increased prevalence of metabolic syndrome,28 higher risk of
high blood pressure,7 and diabetes mellitus.5 The
similar metabolic hazard posed by both regular and diet soft drinks is noteworthy given the lack of calories in the latter; however, other studies have also reported associations of diet soft drinks with weight gain in boys29 and with hypertension in adult women.7
Mechanisms There are several mechanisms that can explain the higher risk of metabolic abnormalities associated with greater consump- tion of soft drinks. These can be broadly grouped under physiological effects, dietary behavior, and the economics of food choice.13
There are several physiological effects of soft drinks that may pose an adverse metabolic risk. Larger consumption of added nutritive sweeteners such as high fructose corn syrup (the primary sweetener in soft drinks) can lead to
weight gain, increased insulin resistance,30,31
a lowering of
HDL-C,32 and an increase in triglyceride levels.27 Typi- cally, in the United States, the high fructose corn syrup added to the beverages contains 55% fructose.30,31 Al-
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