Do All Levels of Physical Activity Reduce the Risk of Developing Metabolic Syndrome? Sometimes More Is Better
Abstract & Commentary
By German H. Rodriguez, MD, and Zehra Siddiqui, DO. Dr. Rodriguez is a Third-Year Resident at the Beth Israel Medical Center/Institute for Family Health Residency in Urban Family Practice, New York. Dr Siddiqui is an Integrative Medicine Fellow at the Institute for Family Health, New York. Dr. Rodriguez and Dr. Siddiqui report no financial relationships relevant to this field of study.
Synopsis: A cross-sectional and longitudinal analysis of the impact of different activity levels on the risk of developing metabolic syndrome on a large random sample of the Danish population found that higher activity levels were associated with a decreased risk of developing metabolic syndrome over the 10-year follow-up period.
Source: Laursen AH, et al. Intensity versus duration of physical activity: Implications for the metabolic syndrome. A prospective cohort study. BMJ Open 2012;2:e001711 doi:10.1136/bmjopen-2012-001711.
Laursen et al analyzed data from the Copenhagen City Heart Study (CCHS) to explore the relationship between leisure time physical activity (LTPA), walking, and jogging on the risk of developing metabolic syndrome. Initially, this study looked at a random sample of men and women living within a specified area of Copenhagen in 1976 with follow ups being conducted in 1981-1983, 1991-1994, and 2001-2003.
The data, constructed from a sample of 10,135 people age 21-98 years, were explored using cross-sectional analysis for the period from 1991-1994. Of these, 6088 participants were included in the longitudinal analysis conducted in the period from 2001-2003. A self-administered questionnaire was used to assess the physical activity habits of those interviewed. Physical activity was divided into LTPA, jogging, and walking habits. LTPA was classified into four group types: 1) sedentary, 2) light PA, 3) moderate PA, and 4) high PA. Walking was divided into three categories depending on the hours per day (0-0.5, 0.5-1, and > 1). Walking and jogging speeds were categorized as slow, average, fast, and very fast. Each person self-reported the amount of activity and the intensity of this activity. Variables such as tobacco use, alcohol consumption, education, and cohabitation also were studied.
Metabolic syndrome was defined according to modified American Heart Association (AHA) criteria1: central obesity, elevated triglycerides, low HDL, and blood pressure above 135/85 mm HG. A higher non-fasting glucose value was used instead of that described in the AHA criteria because no fasting samples were available. If three or more of these factors were present, the person was considered to have metabolic syndrome. Persons with metabolic syndrome at baseline were excluded from the study. Data were compared across groups using one-way analysis of variance. Associations between exercise volume and intensity and metabolic syndrome risk were studied using logistic regression analysis.
The cross-sectional analysis of each of the different baseline demographic characteristics was compared depending on the level of LPTA. In women, the prevalence of metabolic syndrome in the sedentary group was 31% (odds ratio [OR] 0.66; 95% confidence interval [CI] 0.55-0.80; P < 0.001) as compared to 10.9% (OR 0.37; CI 0.19-0.73; P < 0.001) in the group with a high level of LTPA. In men, the corresponding values were 36.8% (OR 0.72; CI 0.59-0.88; P < 0.001) and 13.9% (OR 0.38; CI 0.25-0.59; P < 0.001). This potentially demonstrates a clear association between a higher intensity of LTPA and decreased metabolic syndrome prevalence. There was no clear association between time spent doing a light physical activity such as walking and the risk of developing metabolic syndrome.
At the 10-year follow-up, 3968 subjects were evaluated. Of these, 585 subjects (15.4%) had developed metabolic syndrome. The incidence of metabolic syndrome varied from 19.4% (OR 0.86; CI 0.062-1.19; P < 0.0001) in the sedentary group to 11.8% (OR 0.57; CI 0.41-0.80) in the moderate or highly active groups. There was also a significant difference in the risk of developing metabolic syndrome between the low and high activity level group, but the difference was found to be less significant when compared to the cross-sectional analysis. Walking volume and light physical activity did not decrease the risk of developing metabolic syndrome.
Metabolic syndrome is a steadily growing problem in society. Some early reports found the prevalence to be between 21-23%.2 More recent publications have found the prevalence to be near 34%.3 There has been higher prevalence found in certain groups, including Mexican American men.
It is estimated that common cardiovascular metabolic risk factor clusters (similar to those described for metabolic syndrome) cost the U.S. economy $17.3 billion in lost productivity.4 After accounting for the natural evolution of the components of metabolic syndrome and their long-term complications, it becomes apparent that it is very difficult to accurately determine the real costs to our society.
A myriad of preventive and therapeutic approaches are available in the management of metabolic syndrome.5 Many cross-sectional analyses have studied the impact of physical activity on metabolic syndrome. The lack of longitudinal data has failed to clearly demarcate whether low activity level was a risk for metabolic syndrome or the result of it. Laursen et al aimed to analyze the impact of LTPA, walking, and jogging on the risk of developing metabolic syndrome through both a longitudinal and cross-sectional analysis.
The cross-sectional analysis in this study shows a strong association between higher LTPA and decreased risk of developing metabolic syndrome with a clear dose-response relationship. The data showed that the persons who self-reported a higher activity level were younger and had lower heart rate and blood pressure values. This potentially indicated there was a high level of cardiorespiratory fitness at baseline. This is significant as some authors have reported lower incidence of metabolic syndrome in younger populations.6 The longitudinal analysis also showed similar results but with a weaker correlation when compared to the cross-sectional analysis.
The study had some shortcomings. The assessment of activity level was based on self-administered questionnaires instead of more objective measures. There was no evaluation of the dietary habits of any of the studied population groups. A modified glucose value was used in the metabolic syndrome diagnostic criteria. There was a large difference in the number of persons in the initial analysis (10,135) compared to those included in the fourth survey (3992); 2140 of these patients died in the period between the third and fourth survey. If the investigators had analyzed the cardiovascular causes of death and correlated with activity level, it could potentially test their hypothesis beyond the risk of developing metabolic syndrome to see the impact of different activity levels on mortality in the population studied.
It still remains to be studied what effects the findings of this study have on each of the individual components of metabolic syndrome even though previous analysis of the CCHS data has shown that jogging and walking speed are protective of all-cause and CVD mortality.7
The study authors implied that their analysis of a large Dutch population signified that their results are applicable to larger populations. Even though as primary care providers we would like to agree wholeheartedly, it is important to point out the differences of the mostly homogenous population of Denmark in comparison to the genetically varied population of the United States. In 2010, an estimated 35.7% of the U.S. population older than 20 years of age was obese.8 In 2006, the prevalence of obesity in Denmark was estimated to be 11.4%.9
The bottom line of this study is: 1) higher activity level was associated with a lower risk of developing metabolic syndrome, and 2) low-intensity physical activity such as walking was not associated to a decreased risk of developing metabolic syndrome. Most physicians recommend an exercise regimen to their patients with or at risk for developing metabolic syndrome because it is a low-cost intervention with minimal side effects and numerous health benefits. Health care providers should be supportive of any activity level, given that some patients are limited by concomitant comorbidities and it is important to avoid musculoskeletal injuries that could discourage a previously sedentary patient. Regardless, this study shows us that health care providers should consider endorsing safe increases in activity level to achieve the greatest benefit in every patient because sometimes more actually is better.
1. Grundy SM, et al. Diagnosis and management of the metabolic syndrome: An American Heart Association/National Heart Lung, and Blood Institute Scientific Statement. Circulation 2005;112:2735-2752.
2. Ford ES, et al. Prevalence of the metabolic syndrome among US adults. Findings from the third National Health and Nutrition Examination Survey. JAMA 2002;287:356-359.
3. Ford ES, et al. Prevalence and correlates of metabolic syndrome based on a harmonious definition among adults in the US. J Diabetes 2010;2:180-193.
4. Sullivan PW, et al. Productivity costs associated with cardiometabolic risk factor clusters in the Unted States. Value Health 2007;10:443-450.
5. Deen D. Metabolic syndrome: Time for action. Am Fam Physician 2004;69:2875-2882.
6. Sumner AD, et al. Components of the metabolic syndrome differ between young and old adults in the US population. J Clin Hypertens 2012;14:502-506.
7. Schnohr P, et al. Intensity versus duration of walking, impact on mortality: The Copenhagen City Heart Study. Eur J Cardiovasc Prev Rehabil 2007;14:72-78.
8. Ogden CL, et al. Prevalence of Obesity in the United States, 2009-2010. NCHS Data Brief 2012;82:1-8..
9. Central Intelligence Agency. The World Factbook – Obesity Adult Prevalence Rate. Available at: https://www.cia.gov/library/publications/the-world-factbook/rankorder/2228rank.html. Accessed Dec. 13, 2012.