Human Limits

Two recent scientific papers make it time for a quick update on the topic of fitness and mortality.

 

1.  Fitness vs. Cancer Mortality

The first paper is meta-analysis that summarizes the results of a number of studies on the relationship between fitness and cancer mortality. The results were pretty striking:

 

“Six prospective studies with an overall number of 71 654 individuals and 2002 cases of total cancer mortality were included. The median follow-up time in the studies was 16.4 years. Cardiorespiratory fitness showed a strong, graded, inverse association with total cancer mortality. Using low cardiorespiratory fitness as the reference group, intermediate and high levels of cardiorespiratory fitness were related to statistically significant decreased summary relative risks (RRs) of total cancer mortality of 0.80 [95% confidence interval (CI) 0.67-0.97] and 0.55 (95% CI 0.47-0.65), respectively. Studies that adjusted for adiposity yielded similar results to those that did not adjust for adiposity.”

 

This means that folks with high cardiorespiratory fitness have about half the risk of death from cancer as people in the low fit group.   Usually, in these types of population studies “high fit” is defined as the ability to do “10 mets” of exercise. For example a person with a 10 met exercise capacity can typically run 6 miles (10 km) per hour for few minutes at the end of a maximum exercise test.   This is also an exercise capacity that many if not most middle aged people can attain if they watch their weight and workout regularly.   So while physical activity and cardiorespiratory fitness are not the same thing, many active middle aged people can get to 10 mets. The flip side of this relationship is that most highly fit people are also pretty active and they do at least some higher intensity exercise training which makes it likely they have a 10 met exercise capacity.

 

2.  Fitness vs. Cardiovascular mortality

It has been known for a long time that increased fitness is associated with both lower all-cause mortality and lower cardiovascular mortality. A remaining question is whether this relationship flattens out at about 10 mets. In other words do people who can do more than 10 mets have even lower mortality? The graph below comes from a short report on this topic in almost 70,000 people (64% men) followed for about 12 years including about 38,000 with an exercise capacity of greater than 10 mets. The top panel shows that very high fitness was associated with lower mortality in all age groups. The bottom panel shows the dose response relationships between fitness for the entire study population.   So greater fitness equals lower mortality.

 

 

Summary

Evidence for the protective effects of fitness and its close relative physical activity keeps piling up.   The cancer data is especially heartening, and that fact that things don’t flatten out for fitness vs. mortality at very high levels of fitness is perhaps another piece of objective evidence against the too much exercise “hypothesis”.

 

 

This entry was posted on Wednesday, March 4th, 2015 at 4:04 am and is filed under Current Events, Elite Sports Performance, Research and Health. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.