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Soda Bulge: Soft Drinks and Metabolic Syndrome
By Russell H. Greenfield, MD, Dr. Greenfield is Clinical Assistant Professor, School of Medicine, University of North Carolina in Chapel Hill, and Visiting Assistant Professor, University of Arizona, College of Medicine in Tucson; he reports no financial relationship relevant to this field of study.
Source: Dhingra R, et al: Soft drink consumption and risk of developing cardiometabolic risk factors and the metabolic syndrome in middle-aged adults in the community. Circulation. 2007;116:480-488.
Taking data from participants in the framingham offspring study (a 1971 off-shoot of the original Framingham observational cohort), Dhingra and colleagues sought to determine whether there was an association between soft drink consumption and the development of metabolic risk factors, alone and in combination (metabolic syndrome), in community-dwelling middle-aged adults (mean age = 52.9 years, analysis on 6,039 person-observations). Subjects were free of metabolic abnormalities at baseline, and underwent detailed medical evaluations every four years, at which time the person's medical history was updated and a complete standardized physical examination was performed that included anthropometry, blood pressure measurement, and laboratory assessment of vascular risk factors. At the index examination, subjects were asked to report the average number of 12-oz servings of soft drinks consumed per day in the preceding year. Daily soft drink consumption information was also collected via a physician-administered questionnaire at each study visit from the 4th (1987-1991) to the 6th (1995-1998) examination cycles; that examination questionnaire did not, however, elicit information regarding consumption of regular vs diet drinks (this information was taken from the self-administered Food Frequency Questionnaire (FFQ) completed by participants at the 5th (1992-1995) and 6th examination cycles). With a mean follow-up period of four years, analysis was performed for subjects who had attended any two consecutive examinations from the 4th to the 7th (1998-2001) examination cycles.
Approximately 35% of participants reported consuming > one soft drink/day in response to the examination questionnaire (data based on all 3 examinations); in comparison, only 22% of subjects reported intake of at least one soft drink/day in response to the FFQ. In cross-section, with age and sex-adjusted models, those subjects who consumed > one soft drink/day had a higher prevalence of metabolic syndrome than those drinking < one/day (Odds Ratio [OR] = 1.48). Consumption of > one soft drink/day was associated with increased odds of developing metabolic syndrome (OR = 1.44), obesity (OR = 1.31), increased waist circumference (OR = 1.30), impaired fasting glucose (OR = 1.25), higher blood pressure (OR = 1.18), hypertriglyceridemia (OR = 1.25), and low HDL-C (OR = 1.32). People who had > one soda per day had a 25-32% higher adjusted risk of developing each individual metabolic trait with the exception of hypertension (achieved only borderline significance). Serum total cholesterol, LDL-C, physical activity index, and alcohol consumption did not vary across categories of soft drinks consumed. The higher prevalence of metabolic syndrome with higher intakes of soda was consistent for drinking both sweetened and diet sodas, and stratification of analyses by the presence or absence of caffeine did not appreciably alter results. Dhingra et al conclude that for community-dwelling, middle-aged adults, soft drink consumption, whether diet or regular, is associated with a higher prevalence and incidence of multiple metabolic risk factors, as well as metabolic syndrome.
Results of this trial should send a chill through those of us who enjoy soft drinks on a regular basis, especially among parents. Soft drink consumption has steadily increased for more than three decades, across all age groups, including children, and has been tied to development of obesity and diabetes in children and adolescents, as well as hypertension in adults. Some experts believe that the effects of soft drinks on metabolic traits may vary according to age, sex, and baseline body weight. It is striking that findings of elevated risk for metabolic derangement with increasing intake of soft drinks held true even for both diet and decaffeinated products. This may be partly explained by indications that those who enjoy soda regularly, even diet drinks, often adhere to relatively unhealthy diets high in saturated and trans fats, are more likely to be sedentary individuals, and frequently use tobacco products.
For the purposes of this study, metabolic syndrome was defined as the presence of three or more of the following constellation of findings: waist circumference > 35 inches (women) or 40 inches (men), fasting blood glucose > 100 mg/dL, serum triglycerides > 150 mg/dL, blood pressure > 135/85, and HDL-C < 40 mg/dL (men) or < 50 mg/dL (women). Problems with the trial include recall bias inherent in the use of FFQs, the variance reported between the two employed measures of soda consumption, and lack of generalizability of results (all subjects were Caucasian Americans); the study exhibited high quality in other realms, however, including large sample size, and analytical adjustments made respecting multiple potential confounders.
These alarming results may not surprise some, especially as relates to sweetened soft drinks. High fructose corn syrup is the primary sweetener used to produce soft drinks, and may contribute to weight gain, increased insulin resistance, and elevated triglyceride levels. Concerns exist that other ingredients in popular soft drinks may contribute not only to insulin resistance, but also to systemic inflammation. In addition, leaning towards caffeine-free or no-calorie options does not appear protective.
Dhingra et al are quick to point out the major shortcoming of observational trials, namely that observed associations are not always causal in relation; however, a wealth of data support abandoning soft drinks in favor of healthier fare. Results of this trial give practitioners added fodder with which to help patients avoid metabolic problems and cardiovascular disease.