The first prospective study examining lifestyle habits during the teen years and metabolic syndrome in adulthood was published online January 22, 2013 in Diabetes Care by Patrik Wennberg (Umeå University, Sweden) and colleagues.
The study recorded the television viewing habits and leisure-time physical activity levels of about 1000 16-year-olds in northern Sweden. About 88% of these participants were then evaluated at age 43. The study found that TV and leisure activity levels at age 16 could predict the likelihood of having metabolic syndrome in one's 40s.
Specifically, participants who watched several TV shows each day at age 16 were twice as likely to have metabolic syndrome at age 43 than those who watched one show per week or less at age 16.
When evaluated at age 43, 26.9% of participants had metabolic syndrome and 55% were overweight and obese. Interestingly, high TV watching was associated with certain outcomes — central obesity, low HDL cholesterol, and hypertension at age 43 — while low physical activity levels were associated with some different outcomes — central obesity and high triglycerides.
What does this study mean?
The study clearly shows an association between a sedentary lifestyle and metabolic dysfunction later in life. It has a high follow-up rate (88%), and the longitudinal nature of the study is valuable, according to Marc Bessler, MD, Chief of the Center for Metabolic and Weight Loss Surgery.
Yet as Dr. Bessler explains, the results show an association, not causality, between watching TV and having metabolic syndrome. Because it shows an association rather than causality, the evaluation of TV watching should be considered more of a 'surrogate marker' that likely involves other contributing factors. In particular, the study did not evaluate participants' diets. "This could be a significant factor and was not addressed in the current study."
Dr. Bessler notes that many contributing factors would need to be identified in future research on the role of diet in metabolic syndrome. The European diet differs from the North American diet, and dietary changes have changed dramatically over the last three decades in both continents. Because of these and other undefined factors, it is not possible from this study to determine whether the causes of metabolic syndrome in these participants were due to which factors.
"The study can not answer all of these questions, but it does raise awareness, and argues for increased activity during childhood in order to have a healthier adult population," says Dr. Bessler. Indeed, current research shows children who are obese become obese adults, which is why bariatric surgery is now being studied in adolescents in some specialized centers.
The definition of metabolic syndrome was based on the International Diabetes Federation criteria: waist circumference >80 cm for women and >94 cm for men, plus two or more of the following criteria:
- Increased triglycerides
- Reduced levels of HDL-C, or the "good cholesterol"
- Increased blood pressure
- Increased fasting glucose or diagnosed type 2 diabetes.