Fitness Can't Counteract Fat in Heart Attack Study

Laird Harrison
June 04, 2018

Physical activity does not offset the risk for myocardial infarction that comes with excess body weight, a new analysis from the long-term Tromsø Study suggests.

This finding adds one more piece to the puzzle about the relation between fitness and fatness, said Bente Morseth, PhD, from the Arctic University of Norway in Tromsø.

"It doesn't help that much to be physically active if you are overweight," she told Medscape Medical News.

Experts have long debated whether the increased risk for health problems in overweight people result from inactivity, extra fat, or other factors. Because myocardial infarctions are relatively infrequent, it takes a large, long-term study to measure risk factors.

The Tromsø Study provided such an opportunity because 16,104 people had answered questions about their physical activity in the 1979/80 survey, and data from their hospital records were available from 1979 to 2013, Morseth explained here at the American College of Sports Medicine 2018 Annual Meeting.

At baseline, participants were 20 to 54 years of age, and 47% were women. Over the 34-year study period, 1613 myocardial infarctions were recorded in the study population.

Morseth and her colleagues classified the activity levels of participants on the basis of the physical activity reported in the survey.

"It's a simple question, but it has been validated in many studies," Morseth said.

The Tromsø Study

The 3316 participants who reported taking part in activities such as walking or gardening less than 4 hours a week fell into the low category. The 8963 who reported taking part in such activities at least 4 hours a week fell into the moderate category. The 3278 who engaged in running, bicycling, or a similar exercise at least 4 hours a week fell into the high category. And the 547 who competed in sports fell into the vigorous category.

Over the years, physical activity did confer a benefit. "It's better to be active than inactive," Morseth said.

After adjustment for age, sex, body mass index (BMI), and daily smoking, people in the moderate-activity category were 13% less likely to have a myocardial infarction than people in the low-activity category (hazard ratio [HR], 0.87; 95% confidence interval [CI], 0.77 - 0.98).

People in the high-activity category were 12% less likely to have a myocardial infarction than those in the low-activity category (HR, 0.88; 95% CI, 0.76 - 1.02; P = .02), and people in the vigorous category were 37% less likely (HR, 0.63; 95% CI, 0.42 - 0.95; P = .02).

But the effects of weight were much bigger. After adjustment for age, sex, physical activity, and daily smoking, being overweight increased the risk for myocardial infarction.

Participants with a BMI above 30 kg/m2, considered obese, were 2.7 times more likely to have a myocardial infarction than people with a BMI in the normal range (HR, 2.7; 95% CI, 2.24 - 3.26).

Participants with a BMI of 25 to 30 kg/m2, considered overweight, were 1.54 times more likely to have a myocardial infarction than people with a BMI in the normal range (HR, 1.54; 95% CI, 1.39 - 1.72).

When the researchers divided participants into just two activity categories — active and inactive — and assessed risk for myocardial infarction by weight category, using active participants of normal weight as the reference, they found that risk was only slightly attenuated by activity.

Table. Hazard Ratio for Myocardial Infarction
Weight Category Active Group Inactive Group
Normal 1.00 1.20
Overweight 1.58 1.77
Obese 2.74 3.20

This study relied on self-reported levels of physical activity, not objective measures, which is a limitation of the study, Morseth acknowledged, because other studies have shown that most people overestimate their physical activity.

In addition, there were no data available on body composition. Waist circumference or waist-to-hip ratio can be a more accurate indication of weight category than BMI, which can be misleading in, for example, people who are very muscular. It would have been nice to have these data, but with such a large cohort, the correlation between high BMI and the overweight category is likely to be accurate, she explained.

And the study looked at only one health outcome — myocardial infarction — and did not measure the effects of weight and activity on outcomes such as cancer or diabetes. Morseth said that in the future she hopes to perform an analysis of the same data with death from all causes as the outcome.

The message about fitness and fat might be different when a different outcome is used, said Lina Hermeling, MSc, from Ulm University in Germany.

"In other studies, if you look at another outcome, physical activity does compensate," Hermeling told Medscape Medical News. "In a lot of chronic diseases, it's better being fat and fit than normal weight and unfit."

The study was funded by the Northern Norway Regional Health Authority. Morseth and Hermeling have disclosed no relevant financial relationships.

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SOURCE: Medscape, June 04, 2018. American College of Sports Medicine (ACSM) 2018 Annual Meeting. Abstract 366. Presented May 30, 2018.

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