By Liam Davenport
WebMD Health News
April 13, 2017
DALLAS -- The association between higher body mass index (BMI) and risk of heart failure is largely due to reduced cardiorespiratory fitness (CRF), say US researchers, who suggest that a shift of emphasis in public health messages to focus on fitness more than simply exercise may improve prevention efforts.
In an analysis that included almost 20,000 individuals, Dr Ambarish Pandey (University of Texas Southwestern Medical Center, Dallas) and colleagues found that CRF accounted for 47% of the risk of heart failure hospitalization associated with increased BMI.
The research, which was published online by JACC: Heart Failure on April 5, also showed that change in BMI was not significantly associated with heart failure risk after taking CRF into account.
"Taken together, these findings highlight the fact that much of the observed association between obesity and HF risk reflects the presence of low CRF" and "suggest that a priority should be placed on improving CRF over decreasing BMI," the group writes.
Talking to heartwire from Medscape, Pandey said that, given the difficulties in achieving meaningful reductions in cardiovascular outcomes via lifestyle modifications, focusing health messages on fitness rather than weight per se may achieve greater gains.
"I think one of the reasons for failure of public health initiatives in modifying lifestyle behavior is giving a blanket message of improving lifestyle, which includes healthy eating, exercising, not smoking, and a bunch of other factors," he said.
"I think our study shows that we could target low fitness and exercise more aggressively and more tactically than BMI or body weight and encourage people to exercise more."
Pandey added: "Obviously a higher BMI is bad and lower BMI is better, at least at the normal range, but I think focusing more on fitness and exercise and focusing more on the level of physical activity may be the greater goal in the near future to better improve the risk of cardiovascular diseases."
To examine the relative contributions of BMI and CRF in midlife on the long-term risk of heart failure, the team examined data from the Cooper Center Longitudinal Study, an ongoing prospective investigation that began in 1970.
The participants completed a comprehensive examination, which included cholesterol profile and fasting blood glucose levels; fitness was estimated in metabolic equivalents (METs) on the basis of Balke treadmill time.
The researchers selected from the study 19,485 persons who had no history of MI or stroke at baseline and who had survived to receive Medicare between 1999 and 2009. They gathered data on hospitalizations for heart failure after patients were older than 65 years.
As expected, overweight and obese individuals had a higher burden of traditional cardiovascular risk factors and lower CRF at study entry, whereas those with a higher CRF had lower BMI and risk factor burden.
After 127,110 person-years of Medicare follow-up, during a median period of 6.67 years, there were 1038 heart failure events.
In multivariate analysis that included age, sex, and other variables, a higher BMI was associated with a significantly increased risk of heart failure hospitalization after age 65 years, at a hazard ratio (HR) of 1.25 (95% confidence interval [CI], 1.17 - 1.32) per 3 kg/m2 increase in BMI.
Further adjustment for cardiovascular risk factors slightly reduced the association between BMI and heart failure risk: HR, 1.19 (95% CI, 1.12 - 1.26) per 3 kg/m2 rise in BMI. However, further adjustment for CRF levels markedly reduced the association, to an HR of 1.10 (95% CI, 1.03 - 1.17) per 3 kg/m2 increment in BMI, although it remained significant.
The team calculated that, although established CV risk factors such as blood pressure, diabetes, smoking status, and cholesterol levels accounted for 24% of the heart failure risk associated with BMI, CRF accounted for 47%.
Restricting the analysis to 8683 participants with repeat CRF and BMI measures showed that, after adjustment, change in BMI was significantly associated with risk of heart failure hospitalization, at an HR of 1.08 (95% CI, 1.02 - 1.15) per 1 kg/m2 higher BMI. However, further adjustment for CRF made the association no longer significant, at an HR of 1.05 (95% CI, 0.97 - 1.12) per 1 kg/m2 BMI increase.
Furthermore, change in CRF and heart failure risk were inversely related in a way that accounted for change in BMI, at an HR of 0.91 (95% CI, 0.84 - 0.98) per 1 MET increase in CRF.
In an accompanying editorial , Dr Carl J Lavie (Ochsner Clinic, New Orleans, La) and colleagues say that the current findings support those of previous investigations showing that increases in CRF are associated with reductions in all-cause and cardiovascular disease mortality.
"Although maximal protection may occur at the highest levels of CRF, the biggest 'bang for the buck' is observed with moving a patient out of the low CRF category into a moderate level of CRF," they write.
"This gain in CRF and reduction in risk is within striking range of most adults, who are capable of performing modest levels of physical activity/exercise training."
Lavie and colleagues add that, although the relative benefits of CRF at various levels of BMI and adiposity are needed, the promotion of physical activity/exercise training "is desperately needed throughout the healthcare system, and is a cost-effective method for reducing CVD and mortality, and HF risk as demonstrated by Pandey et al."
Pandey said a randomized controlled trial examining the comparative impact of exercise, diet, and usual care on heart failure risk is required to confirm the findings of their study.
"We are looking at this relationship for myocardial infarction and other cardiovascular diseases, so I think that's something that we want to pursue in the near future," he said. "I would expect the same findings, though."
Pandey et al and Lavie have disclosed no relevant financial relationships.