Is Obesity More Damaging Than Inactivity?

Summarized by Robert W. Griffith, MD
March 27, 2006

Introduction

Which poses the greatest danger to people with regard to coronary heart disease - obesity or inactivity? Both are obviously important, but which is the real culprit? A new study reported in the journal Circulation has attempted to find the answer. Judge for yourself if they were successful. Here's a summary of their findings.

What was done

Researchers at Harvard examined data from more than 88,000 women who were enrolled in the Nurses' Health Study. They were followed for up to 20 years from their enrollment, at which time they were free of cardiovascular disease and cancer. On entry they had full examinations, including body fat measurement, waist measurement, and waist-to-hip ratios.

Every two years the women completed a questionnaire about their medical history and lifestyle. Those who exercised 3½ hours a week or more were considered physically active, and those exercising less than an hour a week were classified as sedentary. A BMI of less than 25 was considered 'lean' while those with a BMI over 30 were classified as 'obese'.

All major coronary events (including nonfatal myocardial infarction and fatal coronary heart disease) were recorded. Based on data from the patients with coronary events, the relative risks for such an event for the four classes of subjects were calculated.

What was found

There were 889 cases of fatal coronary heart disease and 1469 nonfatal heart attacks in the whole population. Eighteen percent of the participants were classified as lean and active; using their risk as a standard (set as 1.0), the relative risks for the other classes are shown in the table:

	Lean (BMI below 25)	Obese (BMI over 30)
Active (3.5 hrs a week)	1.0 (standard)	2.48
Sedentary	1.48	3.44

It can be seen that while the risk for a cardiac event is increased by inactivity 1.48 times, obesity increases the risk by 2½ times if the subject is active, and almost 3½ times if the subject is inactive.

Further evidence of the predominant role of obesity came from examining the role of the waist-to-hip ratios. The risk for a coronary heart disease event was greatest for those women who were sedentary and had the largest waist-to-hip ratios.

Smoking also played a major role. Sedentary obese subjects who smoked were found to have the greatest risk for an event compared to lean, active non-smokers - over 9 times greater, in fact.

What this means

We've published other articles that seem to indicate that 'fat but fit' is not too serious. The findings here belie this concept. The results of this study show clearly that obesity carries a considerably greater risk for a harmful cardiovascular event than inactivity. Dr Frank Wu, the principal investigator, has stated "the harmful effects of obesity cannot be completely offset by increased physical activity."

The waist-to-hip results suggest that abdominal obesity is the problem. Abdominal fat leads to fat cells that secrete increased numbers of cytokines, which can lead to insulin resistance (and then type 2 diabetes) and inflammation, both of which are associated with the development of coronary artery disease.

The data from smoking just adds to the information already available on the risks of this habit. The 'take-away message' from this work is the need to continue to try to keep relatively lean, and to exercise as well. And, of course, to be a non-smoker.

Source

• Obesity as compared with physical activity in predicting risk of coronary heart disease in women. TY. Li , JS. Rana, JE. Manson,  et al., Circulation, 2006, vol. 113, pp. 499--506

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