Researchers have found that cardiorespiratory fitness (CRF) during midlife provides a greater benefit than just living longer. It also means that the onset of serious illnesses is delayed. This is one of the main points of a new study published in JACC, the American College of Cardiology’s flagship journal. The study found that those who had higher levels of CRF during middle age not only lived longer, but also experienced major chronic diseases later in life and spent more years living in good health.

When looking at these results, it is important to separate living longer from living longer without any major chronic disease, such as heart disease, diabetes, kidney disease, cancer, etc. Cardiorespiratory fitness, or CRF, refers to how efficiently your heart and lungs supply oxygen for physical activities.

For many years, it has been established that individuals with higher levels of CRF have a lower risk of dying from heart disease or other illnesses that might result in an early death. Now we see that CRF in midlife is also related to what researchers call health span, or the number of years an individual has lived free from major chronic disease.

The findings of this study suggest that your fitness level during your middle-aged years can affect both how long you will live and when the effects of getting older begin.

The study used the Cooper Center Longitudinal Study (CCLS), which tracked 24,576 adults from 1971 to 2017 and matched the data with Medicare claims from 1999 to 2019. Approximately 25% of the participants were female, and all were considered apparently healthy up to age 65. Participants completed maximal treadmill tests during their preventive healthcare visits. To assess people’s cardiorespiratory fitness levels and classify them into low, moderate, or high fitness, researchers analyzed the cardiorespiratory fitness (CRF) results obtained from those participants.

Researchers used the Medicare Chronic Conditions Data Warehouse to identify health-related outcomes based on the 11 chronic health conditions tracked throughout the study. The definition of disease included multiple methods to assess health status based upon having any of these conditions, the cumulative number of conditions, or the conditions stated clearly as separate entities. The grouping of these 11 chronic health conditions was placed into larger categories by disease type, namely cardiovascular diseases, cardiovascular-kidney-metabolic diseases, and cancer.

The outcome, or finding that stood out, was not so much one large, problematic outcome but rather one large, systematic, ongoing trend. People who maintained high levels of fitness throughout midlife were less likely to develop chronic health conditions and enjoyed an extended period of healthy survival compared with those who were less fit.

The researchers found that each of these 11 chronic health conditions developed at least 1.5 years later for men and women who maintained a high level of fitness than for those who were less fit. This finding was consistent across all 11 chronic health conditions.

When researchers looked at disease in terms of the presence of any one of the 11 chronic health conditions, men who had high fitness levels had 2% longer survival than men with low fitness levels. They also experienced a total of 9% fewer diseases than the low-fit group.

In addition, their overall life expectancy was extended by 3%. Based upon 95% confidence intervals for health span, there was an approximate 1% to 2% improvement for men. There was also an approximate 1% to 17% reduction in the number of chronic diseases for men and an approximate 2% to 4% increase in life expectancy for men.

Similar patterns were found for women.

The overarching finding was the same for both men and women when researchers grouped their respective chronic health conditions into larger clinical categories. Higher-fit individuals typically developed cardiovascular diseases, cardiovascular-kidney-metabolic diseases, and cancers later than their lower-fit counterparts. Additionally, there were fewer illnesses in all of the higher-fit groups.

It is easy to overlook that last point if you only look at lifespan when interpreting this study. The study does not just indicate that individuals with a higher level of fitness lived longer. It also indicates that their number of years of illness was pushed further out in time.

Specifically, individuals with a higher level of fitness experienced a later health-to-disease transition rather than only a later life-to-death transition.

To estimate how people transition from health to disease to death, the researchers used a multivariable model. Using those estimates, they calculated expected health span, expected years of disease, expected number of diseases, and expected overall lifespan for each fitness level.

The study’s conclusion also held true for members in several different subgroups. The same results were found regardless of whether study participants visited doctors before or after 1990, whether they were under or over 45 at the time of measurement, whether they smoked or did not smoke, and whether their body weight fell within the healthy, overweight, or obese range based on BMI.

The consistency across these different subgroups supports the study’s results, even though the study could not definitively demonstrate a cause-and-effect relationship.

The researchers framed the study as a beginning step to find out what role midlife fitness has on health span, disease burden, and lifespan for middle-aged adults who remained otherwise healthy at 65. According to the study’s researchers, they found that if someone is fit in midlife, then they will generally live longer, have fewer chronic diseases, and be healthier at an older age.

“Multimorbidity” refers to a situation where a person has multiple chronic diseases at once.

The study reinforces a common phrase about fitness: fitness does not just refer to athletic performance. It is a measurable indicator of whether significant illnesses will come sooner or later.

Unlike many other risk factors, such as smoking or obesity, people can improve their level of cardiorespiratory fitness.

As noted in the source material, routine physical activity, such as walking briskly, using a bicycle, or doing other variations of aerobic exercise, can boost one’s level of fitness. According to the researchers, even a small amount of increased physical activity may be beneficial for improving fitness at midlife, promoting healthy aging, and improving one’s quality of life later in life.

One of the most forceful findings from the study relates to chronic illnesses. In the high-fitness group, each of the 11 chronic conditions occurred, on average, 1.5 years later than in the low-fitness group. People did not avoid becoming sick from those chronic illnesses. Rather, they simply developed those conditions later.

Public health will focus less on average life expectancy and more on quality of life during the later years of life. Having a long life is not of much value if a person is spending a lot of that time managing several chronic illnesses. The findings from this research suggest that improving one’s fitness level in midlife may allow an individual to have fewer chronic diseases and delay the time until those chronic diseases occur.

The practical application from the study is that the emphasis on having elite fitness is not as important as the fact that an individual has made the effort to obtain a reasonably high level of cardiorespiratory fitness. By engaging in regular aerobic exercise, an individual can increase their level of fitness during midlife. If this occurs, it is very likely that the individual will not only enjoy more years of healthy living, but those years will be healthier.

The study has limitations. It is an observational study and does not show a direct causal relationship between higher levels of fitness in midlife and improved health outcomes. The participants of the study, in general, were already health-conscious individuals, so the findings may not be applicable to the general population.

Despite the study being limited in its applicability, the evidence showed that people who had a higher level of fitness in midlife went on to live longer than those who had a lower level of fitness in midlife. They also had fewer chronic illnesses at an older age.