As most health and fitness enthusiasts are aware, cardiorespiratory fitness (CRF) represents the maximal ability of the body to use oxygen at the cell level. CRF is also known as aerobic fitness, and can be objectively measured in a clinical setting via a maximal treadmill exercise test. Alternatively, CRF can be estimated outside of a laboratory setting via the Cooper 12 minute run test, Cooper 1.5 mile run test, or 1-mile Rockport walk test.
Chronic kidney disease (CKD) is a common condition in the U.S., affecting nearly 15% of the adult population. The severity of CKD is graded on a scale of 1-4, and is determined by how much protein is spilling into the urine and how well the kidneys are filtering the blood. CKD tends to progress slowly over time. On the milder end of the severity continuum, most patients are asymptomatic. Unfortunately, this means that many with CKD are unaware of its presence. Some of the strongest predictors of CKD are older age, hypertension, diabetes, and obesity. Because of increased rates of hypertension, obesity and diabetes over the past four decades, there has been a corresponding increase in CKD. Since dialysis is typically needed 3 days/week for those with severe CKD (i.e. kidney failure), the cost of treatment is enormous from both an economic and psychological aspect. It should be noted that the COVID-19 pandemic has had a devastating effect on those with kidney failure, with disproportional rates of hospitalization and death in that population.
In recent years, it has been shown that regular moderate levels of physical activity are beneficial to kidney health. Here we note that physical activity and CRF are not the same. While there is some correlation between the two, the relationship is only moderate. Physical activity is typically assessed via questionnaire, while CRF as noted previously, can be objectively measured.
With that in mind, Cooper Institute researchers sought to determine if there is a relationship between CRF at midlife and the risk of developing CKD later in life. A total of 17,979 Cooper Clinic patients (22% women) with an average age of 50 years underwent a comprehensive medical exam at baseline. All of the participants were apparently healthy at the time of their exam. Based on their maximal treadmill exercise test performance, as well as their sex and age group, they were placed into CRF categories of Low Fit, Moderate Fit, and High Fit. During an average of 21.4 years of follow-up, including an average of 7.2 years of Medicare data, 2022 new cases of CKD were diagnosed.
In Figure 1 below, the risk of developing CKD among the three CRF categories is shown, using the Low Fit group as the reference group. Moderate and High Fit men and women were 24% and 34% less likely, respectively, to develop CKD compared to the Low Fit men and women.
An additional important finding was that among participants who developed diabetes during the follow-up, those who were Moderate or High Fit were significantly less likely to develop CKD.
In conclusion, those with moderate to high levels of CRF at midlife were significantly less likely to develop CKD later in life when compared to those who were low fit. The authors emphasized that many cases of CKD could be prevented by maintaining a healthy body weight, avoiding tobacco, managing hypertension, consuming a heart-healthy diet, and by achieving at least a moderate level of CRF. Meeting the most recent guidelines for physical activity is a great way to ensure that a moderate level of CRF is attained.
DeFina, L., et al. (2016). The association between midlife cardiorespiratory fitness and later life chronic kidney disease: The Cooper Center Longitudinal Study. Preventive Med. 89:178-183.