Fitness Offsets Kidney Disease Risk From Low Socioeconomic Status

Marlene Busko

July 25, 2022

Having a high degree of physical fitness in middle age appears to counter the increased risk of developing chronic kidney disease (CKD) that comes with having low socioeconomic status, new research suggests.

The researchers analyzed data from men in Finland who participated in the Kuopio Ischemic Heart Disease Risk Factor (KIHD) study. The mean age at enrollment was 53 years, and the participants were followed for roughly 25 years.

Socioeconomic status was determined on the basis of self-reported income, education, occupation, standard of living, and housing conditions. Cardiorespiratory fitness was determined on the basis of peak oxygen uptake (VO2 max) during a stationary bicycle test at the time participants entered the study.

As expected, the men with low socioeconomic status had a greater risk of developing CKD in their 60s and 70s than men with high socioeconomic status, whereas men with high cardiorespiratory fitness had a lower risk of CKD than men with low cardiorespiratory fitness.

Men with low values for both socioeconomic status and cardiorespiratory fitness had a greater risk of developing CKD during follow-up than men with high values for these measures after adjusting for multiple factors associated with risk of kidney disease.

However, men with low socioeconomic status and high cardiorespiratory fitness did not have an increased risk of developing CKD, compared with men with high values for these measures.

The study was published in The American Journal of Medicine.

Regular Physical Activity Reduces Disease Risk Across All Organs

"Regular physical activity is a powerful strategy than can reduce the risk of disease across all organ systems in the human body including the kidneys," lead author Setor Kunutsor, MD, PhD, senior lecturer in evidence synthesis, Bristol University, United Kingdom, summarized in a statement from the university.

"Despite the benefits of physical activity being widely promoted, regular exercise is still low across the world," he said. "More needs to be done to promote physical activity participation across all populations regardless of age, gender, disability, and socioeconomic status."

"It is expected the findings would be similar in women, as the benefits of physical activity extend to women too," Kunutsor speculated in an email to Medscape Medical News.

The results suggest the need for regular physical activity even as people grow older, he said, in light of World Health Organization recommendations (150 to 300 minutes of moderate-intensity physical activity per week or 75 to 150 minutes of vigorous-intensity physical activity per week or an equivalent combination of both).

However, recent global studies show that most people do not meet the recommended targets.

"You can increase your physical activity if your health status allows you to," Kunutsor advises.

"It is a lifelong lifestyle, and it prevents the risk of developing various diseases, such as hypertension, heart disease, heart failure, and diabetes, as well as chronic kidney disease, " he said. "It even slows the progression of these diseases when you already have them.

"Populations at high risk of these chronic diseases, including the socioeconomically deprived, need more education on the substantial benefits of physical activity" to lower the risk of chronic disease and slow disease progression, according to Kunutsor.

More public health messages about this modifiable risk factor for disease are needed, he continued, along with subsidized or possibly even free gym memberships for disadvantaged people.

Primary care providers have a major role to play in promoting physical activity, he added, since they are "the first point of call during the delivery of healthcare."

Socioeconomic Status, Fitness, and CKD Risk

It is well known that lower socioeconomic status and low cardiorespiratory fitness are each associated with an increased risk of CKD, Kunutsor and colleagues write in their article.

They hypothesized that high cardiorespiratory fitness might counter the increased risk of CKD due to low socioeconomic status.

They analyzed data from 2099 men in the KIHD study who lived in and around Kuopio, Finland, and were aged 42 to 61 years from 1984 to 1989 when they enrolled in the study.

The analysis was restricted to men with normal kidney function who had replied to questionnaires about lifestyle and demographics and who had undergone exercise testing to measure cardiorespiratory fitness.

On average, the men's socioeconomic status score was 8.5 (in which scores range from 0 to 25, with 25 indicating the lowest socioeconomic status), and their VO2 max was 30.3 mL/kg/min.

During a median follow-up of 25.8 years, there were 197 CKD events, defined as kidney damage or estimated glomerular filtration rate (eGFR) < 60 mL/min per 1.73 m2 for 3 months or longer.

Low socioeconomic status was associated with a significant increased risk of CKD (hazard ratio [HR], 1.55) compared with high socioeconomic status after adjusting for age, systolic blood pressure, type 2 diabetes, smoking, hypertension, coronary heart disease, total cholesterol, alcohol consumption, eGFR, and physical activity.

High cardiorespiratory fitness was associated with a significant decreased risk of CKD compared to low fitness (HR, 0.66) after adjusting for multiple variables, including socioeconomic status.

Compared to men with high socioeconomic status and high cardiorespiratory fitness, men with low values for both measures had a significant increased risk of CKD (HR, 1.88).

However, there was no significant association between low socioeconomic status/high cardiorespiratory fitness and risk of CKD.

The researchers acknowledge that since this was an observational study, there may be residual confounding or reverse causation, so it cannot prove cause and effect.

Nevertheless, the study suggests that "when you just compare physical activity with income, physical activity is a more protective factor for chronic diseases," concluded Kunutsor.

The study was supported by the Finnish Foundation for Cardiovascular Research, Helsinki, Finland. The authors have disclosed no relevant financial relationships.

Am J Med. Published online July 22, 2022. Full text

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