Fitness Levels in Middle-Age May Predict Survival Decades Later

August 21, 2018

A single blood pressure reading at age 50 won't say much about survival decades later, but one spin on a bicycle ergometer in middle age showing a good fitness level may predict extra years of life, a new analysis suggests.

A cohort from the Copenhagen Male Study including more than 5000 men without known cardiovascular (CV) disease (CVD) was assessed for cardiorespiratory fitness (CRF) at their workplaces.

The single measurement of maximal oxygen consumption (VO2max) showed a graded effect on longevity. Participants with VO2max  in the highest 5% range lived about 5 years longer than those in the bottom 5%. Those in the lower "normal" range also lived longer than those in the bottom fitness tier.

Survival for the men, who averaged about 49 years when they performed the fitness test, was adjusted for possible confounders such as age, self-reported physical activity levels, smoking, and alcohol intake.

It was also adjusted for body mass index (BMI). Interestingly for the randomly selected Danish cohort evaluated in the 1970s, 93% had a BMI of 25 or less at the time.

One criticism of the study might be that it didn't look at CRF over time, observed Magnus T. Jensen, MD, PhD, Copenhagen University Hospital Herlev-Gentofte, Hellerup, Denmark, for theheart.org | Medscape Cardiology.

"But if you see it a different way, it really shows how strong it is, that if you measure your fitness level just one time during your middle age, it gives you a significant piece of information about your health status," said Jensen. Granted, it's a 1970s-era population, "but it does give one an idea of what does it mean to be in bad shape, and the impact in terms of longevity."

Jensen is senior author on the analysis, published August 20 in the Journal of the American College of Cardiology with lead author Johan S.R. Clausen, MD, Bispebjerg University Hospital, Copenhagen, Denmark.  

Importantly, Jensen said, the results were very much the same in a secondary analysis that excluded the 361 men who died within the first decade. That minimized the outcomes effect of any unknown, life-shortening diseases present at baseline that might account for low CRF.

"Because the follow-up was almost half a century, we were able to remove up to 10 years." That it didn't significantly change the predictive value supports the study's one-time CRF findings as causally related to survival decades later, Jensen said.

The analysis looked at 5107 apparently healthy men aged 40 to 59 (mean, 49) years who were recruited at workplaces in Copenhagen from 1970 to 1971 to undergo a bicycle-ergometer fitness examination. During a 46-year follow-up, 4700 (92%) members of the cohort died; the rate of death from CV causes was about 42%.

Their CRF results were stratified based on the middle 90% as the age-adjusted normal range, half of that classified as low-normal and half as high-normal. Taking the lowest 5% (below normal) tier as the reference, performance in higher CRF tiers was associated with significant addition of life-years in a graded fashion. 

Table. Increase in Survival by Baseline Tier of Cardiorespiratory Fitness  

Endpoints Fitness Tier
Bottom 5% (Below Lower Limit of Normal) Lower 45% of Normal Range Upper 45% of Normal Range Top 5% (Above Upper Limit of Normal)
Death, any cause 0.0 (reference) 2.1 (0.7 - 3.4)a 2.9 (1.5 - 4.2)b 4.9 (3.1-6.7)b
Death, any cause, excluding first 10 y of follow-up (%) 0.0 (reference) 1.8 (0.6 - 3.1)c 2.6 (1.4 - 3.9)b 4.3 (2.6-5.9)b
Values are years, along with 95% confidence intervals. Adjusted for baseline age, BMI, self-reported leisure-time physical activity, diabetes, smoking, alcohol, hypertension, and socioeconomic status.

a P = .002.

b P < .001.

c P = .003.

Taking VO2max as a continuous variable, each 1-mL/kg/min increment was associated with a 45-day increase in longevity (P < .001), the report says.

In a secondary analysis, outcomes based on CV mortality were similar to those for all-cause mortality.

The current findings support well-established observations that the greatest survival gains are achieved with improvements at the lowest levels of physical activity, that is, "simply by moving away from the least-fit end of the CRF distribution," write the authors of an accompanying editorial, led by Emmanuel Stamatakis, PhD, University of Sydney, Australia.

However, limitations of the data "precluded conclusive assertions as to what extent low CRF is an independent risk factor for long-term mortality, or if it acts through other pathways involving PA [physical activity] and other known or unknown changes that occurred during the long follow-up period."

CRF may be "the only major physiological risk factor that is not routinely assessed in clinical practice, and despite consistent evidence that shows that even algorithm-estimated CRF improves CVD risk prediction, it is not part of any major CVD risk calculation," the editorialists write.

"Regardless of whether the identified associations were causal or predictive, the current study supported the use of CRF as a clinical vital sign."

It's an objective measure, "and probably much better than just asking your patient how physically active they are," said Jensen. And although the analysis was limited to Danish men, he "doesn't see why the relationship between being physically fit and longevity should be different in women or in other ethnic groups."

The authors of the report and the editorialists report that that have no relevant disclosures.

J Am Coll Cardiol. Published online August 20, 2018. Abstract, Editorial

Follow Steve Stiles on Twitter: @SteveStiles2. For more from theheart.org | Medscape Cardiology, follow us on Twitter and Facebook. 

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