Keeping Active Attenuates -- but Doesn't Eliminate -- Increased CHD Risk Associated With Overweight/Obesity  CME

News Author: Shelley Wood
CME Author: Charles Vega, MD
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From Heartwire — a professional news service of WebMD

May 2, 2008 — In the latest paper to tackle the question of fatness and fitness, an analysis of the Women's Health Study suggests that regular physical activity can significantly reduce — but not eliminate — the risk of coronary heart disease associated with being overweight or obese [1].

The study, which looked [at] almost 39,000 women free of cardiovascular disease (CVD), cancer, and diabetes at baseline, found that women who were normal weight and physically active had the lowest risk of developing coronary heart disease (CHD) over more than 10 years of follow-up. Next up, however, were women who were lean, but not physically active, followed by women who were overweight but physically active.

The study appears in the April 28, 2008 issue of the Archives of Internal Medicine.

Study authors, led by Dr Amy Weinstein (Beth Israel Deaconess Medical Center, Boston), say their analysis reinforces the importance of being physically active and maintaining a healthy body weight, but that the latter is key. "We looked at the role of both physical activity and BMI [body mass index] in the development of heart disease," Weinstein told heartwire. "And what we found is that physical activity played a significant role in lowering the risk of heart disease in those women who are overweight and obese, but it did not completely reduce the risk of being overweight or obese."

The findings are slightly at odds with other studies that have suggested fit may trump fat when it comes to avoiding heart disease, coronary events, or premature death. One such study, published in the Journal of the American Medical Association (JAMA) last year, indicated that obese but fit subjects had a lower risk of dying (over 12 years of follow-up) than normal-weight subjects who did not exercise regularly [2]. But Weinstein and colleagues, in a previous analysis, found that overweight and obese women were more likely to develop diabetes, regardless of whether they were physically active [3].

Risk reduced by physical activity

In the current study, Weinstein et al report that of the 948 cases of incident CHD that occurred over follow-up, the majority were in women who were overweight or obese. Compared with lean, active women, women who were obese and inactive were two and a half times more likely to die of CHD, have a myocardial infarction (MI), or require coronary artery bypass graft (CABG) surgery or percutaneous coronary intervention (PCI). But women who were normal weight but inactive were still less likely to have a CHD event than women who did regular physical activity but were overweight.

Relative risk of CHD, compared with fit, normal-weight women

The authors postulate that physical activity, by improving endothelial function and reducing vascular resistance, may counteract the adverse effects of increased adiposity on atherosclerosis development, coagulability, and inflammation.

Fit vs fat

As for the ongoing debate over fitness and fatness, Weinstein pointed out that their particular study looked at self-reported activity — not just exercise regimens, but amount of activity in day-to-day life. Other studies have specifically measured fitness level, using treadmill tests or other methods, and this may be one reason that results have differed. She also pointed out that in the current study, overweight women who were expending at least 1500 kilocalories a week (ie, 50% more than the 1000 kilocalories that defined "active" in the study) had no statistically significant increased risk of CHD over normal-weight, active women. That said, the study was underpowered to specifically address whether a higher level of physical activity might counteract the effects of being overweight or obese.

"The reason we like the self-reported physical activity measure is that it gives us a sense, in terms of a public-health message, of what someone needs to do to reduce her risk. For example, the surgeon general says that a woman should exercise moderately most days of the week, and that's about 1000 kilocalories per week, and that's how we performed our analyses," Weinstein explained. "This study shows that the guideline of about 1000 kilocalories per week, or a half an hour of moderate activity most days of the week, truly makes a significant difference in lowering your risk of heart disease. But in order to really think about reversing the risk and getting back to the risk of a normal-weight individual, people need to think about lowering their body weight."

Commenting on the study for heartwire, Dr Steven Blair (University of South Carolina, Columbia), senior author on the JAMA paper last year, also highlighted the differences of measuring fitness and relying on self-reported activity.

"A major difference between this new study and our work on fitness and fatness is that our reports include data on measured fitness from a maximal exercise test on a treadmill," Blair explained. "That is, we have an objective measure of cardiorespiratory fitness." In his recent JAMA paper, for example Blair and colleagues used actual laboratory measures of body adiposity and fat distribution from underwater weighing, skinfold measurements, and waist circumference.

"The Women's Health Study used self-report of physical-activity habits and self-reported height and weight to calculate body-mass index," Blair continued. "Another difference is that many of our reports have been on all-cause mortality, and the WHS study used the end point of self-reported coronary heart disease. Perhaps all of these differences in methods help explain the different results."

The National Institutes of Health, Bethesda, Maryland, supported this study. Two of the study authors have obtained funding. A complete list of disclosures is available in the original article.

Sources

1. Weinstein AR, Sesso HD, Lee IM, et al. The joint effects of physical activity and body mass index on coronary heart disease risk in women. Arch Intern Med. 2008;168:884-890.
2. Sui X, LaMonte MJ, Laditka JN, et al. Cardiorespiratory fitness and adiposity as mortality predictors in older adults. JAMA. 2007;298:2507-2516.
3. Weinstein AR, Sesso HD, Lee IM, et al. Relationship of physical activity vs body mass index with type 2 diabetes in women. JAMA. 2004;292:1188-1194.

The complete contents of Heartwire, a professional news service of WebMD, can be found at www.theheart.org, a Web site for cardiovascular healthcare professionals.

Clinical Context

Exercise can have a significant impact on the overall mortality among men, according to research by Lee and colleagues. Their observational cohort study, which was published in the March 1999 issue of the American Journal of Clinical Nutrition, observed 21,925 men and demonstrated that, in lean men, physical fitness reduced the risk for mortality by half. In addition, obese, fit men had lower rates of all-cause and cardiovascular mortality vs men who were lean but unfit. Fitness also reduced the risk for mortality among men with a high waist circumference to levels below those of unfit men with a low waist circumference.

The current study examines the relative effects of physical activity and BMI on the risk for CHD among participants in the Women's Health Study.

Study Highlights

• The Women's Health Study consisted of US female health professionals aged 45 years and older. Women with a history of CVD were excluded from the research protocol.
• A baseline history and physical examination was performed, including measurement of subjects' BMI. Physical activity was assessed by participant self-report, and these reports appeared to be reliable on validity testing.
• Subjects were observed for a mean of 10.9 years for incident CHD, as defined by MI, CABG, coronary angioplasty, or death from CHD. Events were verified in the medical record.
• Women with a BMI of less than 25 kg/m² were classified as normal weight, whereas overweight was defined by a BMI of 25 to less than 30 kg/m². Obesity was defined by a BMI of 30 kg/m² or more. Women who spent at least 1000 kcal on recreational activities weekly were considered active.
• The main outcome of the study was the effect of physical activity and BMI on the risk for incident CHD. This result was adjusted for potential confounding variables.
• 38,897 women had data available for analysis. The mean age was 54 years. The median energy expenditure was 578 kcal/week, and the mean BMI was 26 kg/m².
• 34% of subjects met current national recommendations for exercise, 51% of women were normal weight, 31% were overweight, and 18% were obese.
• There were 948 CHD events during follow-up. Both physical activity and BMI were independent predictors of CHD events.
• Compared with active, normal-weight women, the adjusted hazards ratio of CHD was 2.53 for obese, inactive women. This risk value was 1.88 among overweight, inactive women.
• Physical activity attenuated the risk for CHD among obese women (adjusted hazard ratio, 1.87) as well as overweight women (adjusted hazard ratio, 1.54). However, their risk for CHD still remained significantly elevated vs active, normal-weight women.
• Among women at a normal weight, physical activity did not significantly attenuate the risk for incident CHD.
• The researchers examined walking alone as a recreational activity, and walking promoted significant reductions in the risk for CHD among obese and overweight women.

Pearls for Practice

• Previous research suggests that physical fitness is more important than body composition in the risk for mortality among men.
• The current study demonstrates that physical activity can attenuate, but not eliminate, the increased risk for CHD associated with overweight and obesity among women.

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