The choice of a metabolic-syndrome generation: Soft-drink consumption associated with increased metabolic risk

July 23, 2007

Boston, MA - Drinking more than one soft drink daily is associated with a higher risk of developing adverse metabolic traits, as well as developing the metabolic syndrome, a new study has shown[1]. Interestingly, it doesn't matter if the soda consumed is the diet variety, those with zero calories, as investigators showed these also increased the burden of metabolic risk in middle-aged adults.

"That was one of the more striking aspects of this study," lead investigator Dr Ramachandran Vasan (Boston University School of Medicine, MA) told heart wire . "It actually doesn't matter if the soft drink is regular or diet. There was an association of increased risk of developing the metabolic syndrome with both types of drinks."

Discussing the findings, which are published online July 23, 2007 in Circulation, Vasan said that the consumption of soft drinks has doubled to tripled between 1977 and 2001. During this same time period, soft-drink sizes have also increased to staggering proportions. With evidence that soft-drink consumption is linked with weight gain and obesity as well as an increased risk of diabetes, the investigators questioned whether soft-drink consumption in adults, in amounts that are seemingly innocuous, like one per day, posed any metabolic hazard.

The investigators, led by Dr Ravi Dhingra (Harvard Medical School, Boston, MA), related the incidence of metabolic syndrome and its components to soft-drink consumption in more than 6000 individuals participating in the Framingham Heart Study. Information on daily consumption of soft drinks was collected via a physician-administered questionnaire, with information on the type of soft drink—diet or regular—collected in later questionnaires. Metabolic syndrome was defined as the presence of three or more of following risk factors: excess waist circumference, high blood pressure, elevated triglycerides, low HDL-cholesterol levels, and high fasting glucose levels. 

In a cross-sectional analysis of the data, investigators report that those consuming more than one soft drink daily had a 48% higher prevalence of metabolic syndrome than those who drank less than one soft drink per day. In a longitudinal analysis of more than 6000 subjects free from metabolic syndrome at baseline, drinking more than one soft drink daily was associated with a 44% greater risk of developing metabolic syndrome and with developing four out of five components of metabolic syndrome. There was a trend toward an increased risk of developing high blood pressure, but this association did not reach statistical significance.

Odds ratio of developing components of metabolic syndrome and metabolic syndrome in adults consuming >1 soft drink daily

Component of the metabolic syndrome Multivariable-adjusted odds ratio (95% CI)
Incidence of increased waist circumference (>102 cm for men and >88 cm for women) 1.30 (1.09-1.56)
Incidence of impaired fasting glucose ( > 5.5 mmol/L or diabetes) 1.25 (1.05-1.48)
Incidence of high blood pressure (>135/85 mmHg or on treatment) 1.18 (0.96-1.44)
Incidence of hypertriglyceridemia (>1.7 mmol/L or on treatment) 1.25 (1.04-1.51)
Incidence of low HDL cholesterol (<1.03 mmol/L for men and <1.30 mmol/L for women or on treatment) 1.32 (1.06-1.64)
Incidence of metabolic syndrome (3 of 5 components) 1.44 (1.20-1.74)

In a smaller sample of participants who had data available regarding the type of soft drink consumed, researchers observed that that those who consumed one or more drinks of diet or regular soda per day had a 50% to 60% increased risk of developing new-onset metabolic syndrome.

Odds ratio of developing the metabolic syndrome in adults consuming >1 soft drink (diet or regular) daily

Component of the metabolic syndrome Multivariable-adjusted odds ratio (95% CI)
Diet soft drink, >1/d 1.53 (1.10-2.15)
Regular soft drink, >1/d 1.62 (0.96-2.75)

Despite the fact that diet soda has zero calories, the findings are not entirely surprising, said Vasan, as diet soft drinks have been previously linked with poor health outcomes in children, such as weight gain and high blood pressure. In terms of theories explaining the association between soft-drink consumption and the metabolic syndrome risk, Vasan said there are no definitive answers yet.

"Individuals who drink soda tend to have a greater intake of calories, they consume more saturated and trans fats, they consume less fiber and dairy products and have a more sedentary lifestyle," he said. "We adjusted for a number of these variables, but even after the adjustment, there was a significant association that was evident. It makes the case that maybe you can't fully adjust for lifestyle factors, and it might be a lifestyle/dietary background thing driving this."

In addition, Vasan said diet soda might also induce a conditioning response in which the soft drinks promote a dietary preference for sweeter foods. Also, because diet soda is liquid, this has the effect of individuals eating more at the next meal, mainly because liquids are not as satiating. And finally, the brown caramel in soda has been linked with tissue damage and inflammation, which might contribute to the increased risk. All of these theories, however, are debated in literature.

"Clearly, these findings are sufficiently intriguing that scientists now have to help us understand better why we see this association," said Vasan. "We are not inferring causality from this analysis. It is just an association, so we need to turn to the scientists who are better positioned to help us understand the association more."

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