Even relatively small changes in cardiorespiratory fitness (CRF) are associated with “considerable” impact on clinical symptoms and mortality risk among individuals with and without cardiovascular disease, new observational data in United States veterans suggest.
“We had a few surprises,” Peter Kokkinos, PhD, Robert Wood Johnson Medical School, New Brunswick, N. J., and the VA Medical Center, Washington, told this news organization. “First, the mortality risk was greatly attenuated in those who were moderate- and high-fit at baseline, despite a decline in fitness over time. In fact, in those with no CVD, the risk was not significantly elevated even when CRF declined by at least one MET [metabolic equivalent of task] for the moderate-fit and two or more METs for the high-fit group.”
“Second,” he said, “Our findings suggest that the impact of CRF on human health is not ephemeral, but rather carries a certain protection over time. Third, the changes in CRF necessary to impact mortality risk are relatively small (> 1.0 METs). This has a substantial clinical and public health significance.”
The study was published online in the Journal of the American College of Cardiology.
CRF up, mortality risk down
Dr. Kokkinos and colleagues analyzed data from 93,060 U.S. veterans; of these, 95% were men (mean age, 61.4 years) and 5% were women (mean age, 57.1 years). Overall, 72% of participants were White; 19.8%, African American; 5.2%, Hispanic; 1.9%, Native American, Asian, or Hawaiian; and 1.2%, unknown.
Participants were assigned to age-specific fitness quartiles based on peak METs achieved on a baseline exercise treadmill test (ETT). Each CRF quartile was stratified based on CRF changes (increase, decrease, no change) on the final ETT, with at least two ETT assessments at least 1 year apart.
The mean follow-up was 5.8 years (663,522 person-years), during which 18,302 deaths (19.7%) occurred, for an average annual mortality rate of 27.6 events per 1,000 person-years.
CRF was unchanged in 25.1% of the cohort, increased in 29.3%, and decreased in 45.6%. The trend was similar for those with and without CVD.
Significant differences were seen in all variables across CRF categories. In general, body weight, body mass index, CVD risk factors, and overall disease burden were progressively more unfavorable for those in the lowest CRF categories.
Conversely, medication use was progressively higher among those in low CRF categories.
After adjustment, higher CRF was inversely related to mortality risk for the entire cohort, with and without CVD. Cumulative survival rates across CRF categories declined progressively with increased fitness.
For patients with CVD (hazard ratio, 1.11), other significant predictors of all-cause mortality for patients were age (HR, 1.07), body mass index (HR, 0.98), chronic kidney disease (HR, 1.85), smoking (HR, 1.57), type 2 diabetes (HR, 1.42), hypertension (HR, 1.39), and cancers (HR, 1.37).
Generally, changes in CRF of at least 1.0 MET were associated with inverse and proportionate changes in mortality risk, regardless of baseline CRF status. For example, they note, a CRF decline of > 2.0 METs was associated with a 74% increased mortality risk for low-fit individuals with CVD, and a 69% increase for those without CVD.
A second analysis was done after excluding patients whose CRF declined and who died within 2 years of their last ETT, to account for the possibility that higher mortality rates and CRF declines were consequences of underlying disease (reverse causality). The association between changes in CRF and mortality risk persisted and remained similar to that observed in the entire cohort.
The authors add, “It is noteworthy that CRF increased by at least 1 MET in approximately 29% of the participants in the current study and decreased in approximately 46% of participants. This finding underscores the need to promote physical activity to maintain or increase CRF levels in middle-aged and older individuals.”
“Our findings make a persuasive argument that CRF is a strong and independent determinant of all-cause mortality risk, independent of genetic factors,” Dr. Kokkinos said. “We know that CRF is determined to some degree by genetic factors. However, improvements in aerobic capacity or CRF over time are largely the outcomes of regular engagement in aerobic activities of adequate intensity and volume.”
“Conversely,” he said, “a decline in CRF is likely the result of sedentary behavior, the onset of a chronic condition, or aging.”
If genetics were the sole contributor to mortality risk, then changes in CRF would not influence mortality risk, he concluded.
CRF impact “woefully underestimated”
Barry A. Franklin, PhD, past chair of both the American Heart Association’s Council on Physical Activity and Metabolism and the National Advocacy Committee, said the study substantiates previous smaller studies and is a “seminal” work.
“CRF is woefully underestimated as an index of health outcomes and survival,” said Dr. Franklin, director of preventive cardiology and cardiac rehabilitation at Beaumont Health in Royal Oak, Mich. “Moderate to vigorous physical activity should be regularly promoted by the medical community.”
Dr. Franklin’s recent review, published in Mayo Clinic Proceedings, provides evidence for other exercise benefits that clinicians may not be aware of, he noted. These include:
- Each 1 MET increase in CRF is generally associated with approximately 16% reduction in mortality.
- At any given risk factor profile or coronary calcium score, unfit people have 2-3 times the mortality as their fit counterparts.
- Fitness is inversely related to annual health care costs (each 1 MET increase in CRF is associated with approximately 6% lower annual health care costs).
- Physically active people hospitalized with acute coronary syndromes have better short-term outcomes (likely because of a phenomenon called ‘exercise preconditioning’).
- Fit people who undergo elective or emergent surgical procedures have better outcomes.
- Regular physical activity is a common characteristic in population subsets who routinely live into their 90s and to 100+.
Dr. Franklin had this advice for clinicians seeking to promote CRF increases of 1 MET or more among patients: “Sedentary people who embark on a walking program, who over time increase their walking speed to 3 mph or faster, invariably show at least a 1 MET increase in CRF during subsequent peak or symptom-limited treadmill testing.”
“Another general rule is that if an exercise program decreases heart rate at a given or fixed workload by about 10 beats per minute [bpm], the same treadmill workload that initially was accomplished at a heart rate of 120 bpm is now being accomplished at a heart rate of 110 bpm,” likely resulting in about a 1 MET increase in fitness.
“Accordingly,” he added, “a 20-bpm decrease would suggest a 2 MET increase in fitness!”
In a related editorial, Leonard A. Kaminsky, Ball State University, Muncie, Ind. and colleagues, write, “We agree with and believe the conclusion, reached by Kokkinos et al., bears repeating. We (again) call on both clinicians and public health professionals to adopt CRF as a key health indicator.”
“This should be done by coupling routine assessments of CRF with continued advocacy for promoting physical activity as an essential healthy lifestyle behavior,” they write.
No funding or relevant financial relationships were disclosed.
A version of this article first appeared on Medscape.com.