Heart Disease Risk Linked To Lack of Exercise Not Just Obesity

Summary
Obesity is a universal health risk. Some past studies have found that higher body mass index (BMI), a measure of body fat, is associated with lower risk of death in patients suffering from coronary artery disease (CAD). This study, however, refutes these findings. It indicates that having lower fitness leads to almost a threefold increase in mortality in CAD patients. It also notes that an increase of one unit in peak oxygen uptake (VO2 peak), an indicator of exercise fitness, leads to a 9% decrease in mortality in the same group.

Introduction
Obesity is a known health hazard. It is linked with diseases of the heart and metabolic disorders like diabetes. However, a paradox regarding obesity and CADs conditions such as angina and myocardial infarction exists. It seems that a higher body mass index – an index of obesity – is associated with fewer deaths due to heart disease. In contrast, a good level of cardiorespiratory fitness is known to reduce the risk of mortality in healthy populations. Some studies that examined the joint impact of fitness and adiposity on the risk of death showed that obese subjects have the same mortality rate as unfit subjects of a normal weight. These studies had used metabolic equivalents to document exercise capacity. The current study measured a better indicator of exercise capacity – VO2 peak – to study its relation to deaths in obese people. It also used a better measure of adiposity, or fat storage, which is the waist-to-hip ratio (WHR).

Methodology

  • Data on all patients registered for cardiac rehabilitation at the Mayo Clinic from 1993 to June 2007 was obtained.
  • The details of their cardiopulmonary exercise tests performed on a motor-driven treadmill and VO2 peak measurements were noted. The WHR was calculated for each participant.
  • Of the 855 participants, the number of people living, as on February 1, 2010, was noted.
  • Statistical tests were performed to find links between death, obesity, and exercise capacity.

Results

  • Of the 855 participants, 169 had normal body weight, 435 were overweight, and 251 were obese; 428 had a low fitness level and 427 had a high fitness level.
  • In total, 159 deaths took place during a mean follow-up of 9.7 years.
  • Out of the 449 who could exercise on the treadmill for a longer time, only 38 people had died, whereas 121 people had died out of the 406 people who could exercise for a shorter time. Being in the lower fitness category was associated with an almost threefold increase in mortality in CAD patients.
  • An increase of one unit in VO2 peak was associated with a 9% decrease in mortality.

Shortcomings
The study used BMI as an indirect measurement of body fat. The participants were people suffering from CAD and who attended a rehabilitation program, which included exercises. People who suffered from CAD but did not participate in exercise rehabilitation were excluded. The analysis for such a group might be different.

Conclusion
The so-called “obesity paradox” states that in people suffering from CAD, obesity actually lowers the risk of death due to this disorder. This is strange, as obesity is considered a universal health risk. The current study used VO2 peak, a better marker of exercise fitness, to study mortality in people suffering from CAD. The findings suggest that low fitness levels, shorter time on the treadmill before symptoms appear, and a high waist-to-hip ratio are linked to higher mortality. After adjusting for WHR, obesity was associated with a 40% higher likelihood of dying, when compared with people having normal weight. The study indicates that the obesity paradox might not exist if parameters like WHR and direct body fat measurement are used instead of BMI.

For More Information:
Combined Effect of Cardiorespiratory Fitness and Adiposity on Mortality in Patients with Coronary Artery Disease
Publication Journal: American Heart Journal, 2011
By Kashish Goel, MD; Randal J Thomas, MD
From the Wayne State University, Detroit, Michigan, and Mayo Clinic, Rochester, Minnesota

*FYI Living Lab Reports Are Summaries of the Original Research.



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