High levels of aerobic fitness appeared to benefit people in middle age, with lower mortality -- and a dose response -- in a large retrospective cohort study.
Among patients undergoing exercise treadmill testing (ETT) from 1991 to 2014 at the Cleveland Clinic, risk-adjusted all-cause mortality was inversely related to cardiorespiratory fitness (CRF) and was lowest among elite performers in comparison to the poorest performers (adjusted HR 0.20, 95% CI 0.16-0.24; P<0.001), reported Wael Jaber, MD, and colleagues at the clinic in .
The data even showed improved survival when comparing elite and high performers (adjusted HR 0.77, 95% CI 0.63-0.95; P =0.02), the investigators found.
Previous research findings have pointed to adverse cardiovascular results linked with regular vigorous exercise and have challenged the benefits of working out and staying fit, noted Jaber and coauthors. Thus, the current study should counter those concerns.
A unique aspect of the study is that it is a large study with long-term follow-up at a major medical center, commented Carl "Chip" Lavie, MD, of the John Ochsner Heart and Vascular Institute in New Orleans. The researchers "showed progressive benefits across the entire spectrum of CRF, even showing benefit in the super high compared with just high," said Lavie, who was not involved in the study.
He pointed out, though, that the present study did not evaluate physical activity or exercise levels, only CRF.
"No one has suggested harm of having a higher CRF," Lavie argued. "It should be kept in mind that although physical activity and exercise training is the main way to improve one's CRF, so most who have very high levels probably have high levels of physical activity and exercise, a substantial part of CRF may be inherited."
John Higgins, MD, MBA, MPhil, of Lyndon B. Johnson General Hospital in Houston, who also was not part of the study team, commented that the research hasn't closed the door on possible adverse effects of intense training. Like Lavie, he noted that Jaber's group had no data on the participants' actual physical activity habits.
"So we cannot exclude [that] there may still be some issues with overtraining or overdoing the exercise to extremes with respect to total weekly volume, and not allowing an appropriate recovery after exercise," Higgins said.
But he also agreed that the study still supports the message that exercise is medicine: "Perhaps we should be having our 50+ year-old patients spend some time each week doing some type of high-intensity interval training."
Additional Study Details
Jaber's group evaluated 122,007 patients, with a mean age of 53.4 years and of whom 59.2% were male. Among these, 13,637 died during the 1.1 million person-years of study observation.
The investigators assessed the patients as they underwent symptom-limited exercise treadmill testing stratified by age- and sex-matched cardiorespiratory fitness into performance groups that included: low (<25th percentile), below average (25th-49th percentile), above average (50th-74th percentile), high (75th-97.6th percentile), and elite (≥97.7th percentile).
The results showed an increase in all-cause mortality linked with reduced cardiorespiratory fitness when comparing low and elite fitness (adjusted HR 5.04, 95% CI 4.10-6.20; P<0.001). A similar trend was found when comparing below average and above average performance groups (adjusted HR 1.41, 95% CI 1.34-1.49; P<0.001).
Other data emphasized that the adjusted mortality risk was expectedly highest in the lowest performing groups and in most cases surpassed that of the following typical clinical risk factors:
- Coronary artery disease: adjusted HR 1.29, 95% CI 1.24-1.35; P<0.001
- Smoking: adjusted HR 1.41, 95% CI 1.36-1.46; P<0.001
- Diabetes: adjusted HR 1.40, 95% CI 1.34-1.46; P<0.001
A subgroup analysis pointed to the benefits of elite over high performance for patients with hypertension (adjusted HR 0.70, 95% CI 0.50-0.99; P=0.05) and patients aged 70 years or older (adjusted HR 0.71, 95% CI 0.52-0.98; P=0.04).
Jaber and colleagues acknowledged that the study was retrospective and had unmeasured potential confounding variables including socioeconomic status and race. Also, the study population may not represent the general population distribution of estimated functional capacity for the purpose of identifying elite performers, and the results do not speak to the connection between long-term levels of fitness and mortality. The findings on cardiorespiratory fitness relied on a single ETT, the investigators noted.
Disclosures
Jaber, Higgins, and Lavie did not report any financial disclosures.
Primary Source
JAMA Network Open
Mandsager K, et al "Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing" JAMA Netw Open. 2018; DOI:10.1001/jamanetworkopen.2018.3605.