Reduced eGFR Associated with Increased Sedentary Time in Canadian Study

In the general population, ≥50% of awake time is spent in sedentary activities. Studies have shown that sedentary behavior, independent of physical activity level, is a risk factor for adverse health outcomes, including increased risk for diabetes and all-cause and cardiovascular mortality, and higher rates for chronic disease. There is an association between increased sedentary time and lower health-related quality of life, as well as an increase in the prevalence of depressive symptoms and mood disorders.

 Compared with the general population, those with chronic kidney disease (CKD) have low levels of physical activity and levels of physical decline as the severity of CKD increases. The associations of poor outcomes seen in the general population in those with lower physical activity levels are matched in the population with CKD, including increased mortality, increased symptom burden related to dialysis, and decreased quality of life.

Previous studies examining physical activity behavior among patients with CKD commonly relied on self-reported measures derived from questionnaires. Due to the inability to capture low-intensity activities or short periods of activity (<10 minutes), the questionnaires were often limited in quantification of the degree of physical activity compared with the gold standard of accelerometry. Further, most questionnaires did not independently measure or include questions related to sedentary time.

Tamara Glavinovic, MDCM, and colleagues conducted a cross-sectional national survey in Canada to examine the association between CKD and gold standard measures of sedentary time. Using data from the Canadian Health Measures Survey (CHMS) component related to activity monitoring, the researchers sought to test the hypothesis that, independent of age and comorbid conditions, there would be an association between reduced kidney function and a marked increase in sedentary time, as measured using accelerometry. Study results were reported in the American Journal of Kidney Diseases [2018;72(4):529-537].

The CHMS, a nationally representative voluntary survey of Canadians 3 to 79 years of age (n=16,019) was launched in 2007; the current study included data from the first three cycles (2007-2009, 2009-2011, and 2012-2013). There were 10,995 individuals ≥18 years of age in the first three cycles. Of those, there were 2955 from cycle 1, 2976 from cycle 2, and 2513 from cycle 3 with valid activity monitoring using accelerometry (total=8444).

Participants received an Actical accelerometer (Philips Respironics) to be worn over the dominant hip during waking hours for a total of 7 days (showering and swimming included). Midnight of the day the participant received the monitor signaled the start of data collection. The categorical outcome (primary) of interest was ordinal, representing quartiles of sedentary time. Participants were stratified into quartiles of percentage of sedentary time (n=2111 per quartile); quartile 1 included those with the lowest proportion of sedentary time. The continuous outcome (secondary) was the proportion of time spent sedentary.

Individuals were further classified into groups based on kidney function, as measured by estimated glomerular filtration rate (eGFR) using the CKD Epidemiology Collaboration equation. The three groups were: (1) eGFRs >60 mL/min/1.73 m2; (2) eGFRs 45-60 mL/min/1.73 m2; and (3) eGFRs <45 mL/min/1.73 m2.

Mean overall wear time of the accelerator was 5486 minutes. In Q4 (the most sedentary group), the proportion of wear time spent sedentary was 80.7% compared with 58.0% in Q1 (the least sedentary group), P<.01. Mean sedentary times in Q2 and Q3 were 68% and 74%, respectively. Those in Q4 were older and more likely to be women; the burden of comorbidity, including higher mean body mass index and higher blood pressure, was substantially higher compared with those in the other three quartiles (P<.001). Q4 participants also had a 4-fold increase in the prevalence of diabetes, a 6-fold higher increase in the prevalence of heart disease, and a nearly 10-fold higher prevalence of reduced eGFR (P<.001).

There were 322 individuals with eGFR <60 mL/min/1.73 m2; they were older, had lower levels of hemoglobin, more comorbid conditions, and lower amounts of accelerometer wear time compared with those in the other two eGFR groups. The proportion of mean sedentary time in the group with eGFRs >60 mL/min/1.73 m2 was 69.9% (n=8072); in the group with eGFRs 45 to 60 mL/min/1.73 m2, the proportion of mean sedentary time was 75.9% and in those with eGFRs <45 mL/min/1.73 m2, it was 80.5% (P<.001).

In logistic regression analysis, in comparison with those with eGFRs >60 mL/min/1.73 m2, the likelihood of being in a quartile with higher sedentary time was nearly 2-fold higher in those with eGFRs 45 to 60 mL/min/1.73 m2 (odds ratio [OR], 1.7; 95% confidence interval [CI], 1.2-2.3) and 4-fold higher in those with eGFRs <45 mL/min/1.73 m2 (OR, 4.2; 95% CI, 2.5-7.3).

In the CKD subgroup, there was an association between every 10 mL/min/1.73 m2 increase in eGFR and a 40% likelihood of being in a more sedentary quartile. There was also an association between the presence of diabetes and a 2-fold increased risk of being in a more sedentary quartile (OR, 2.68; 95% CI, 1.56-4.49) and between the presence of arthritis and a 2-fold increased risk of being in a more sedentary quartile (OR, 2.32; 95% CI, 1.43-3.77).

In a fully adjusted model of linear regression, compared with those with eGFRs >60 mL/min/1.73 m2, there was an association between eGFRs <45 mL/min/1.73 m2 and an absolute increase of 5.41% (95% CI, 3.8%-7.0%) of time spent sedentary, and eGFRs of 45 to 60 mL/min/1.73 m2, with 3.58% (95% CI, 1.6%-5.6%) additional time spent sedentary.

Even in Q1, for a participant with an average total weekly wear time of 5628 minutes, decreased eGFRs of 45 to 60 mL/min/1.73 m2 or eGFRs <45 mL/min/1.73 m2 would transplant into an additional 202 and 304 minutes spent sedentary per week, respectively. In Q4, for a participant with an average total weekly wear time of 5238 minutes, reduced eGFR would add 187 (95% CI, 82-293) and 283 (95% CI, 199-367) sedentary minutes per week depending on the degree of impairment.

The researchers cited some limitations to the study, including the cross-sectional and observational design, reliance on a single eGFR measurement, and the inability to determine how sedentary time was affected by the severity of comorbid conditions.

In summary, the researchers said, “In this nationally representative cross-sectional analysis, we clearly demonstrate that reduced eGFR is independently associated with a marked increase in sedentary time. The magnitude of this association is stronger than that associated with increasing age and/or the presence of diabetes and calls for further study to explore the biology and psychosocial factors behind reduced kidney function and sedentary behavior.

“Finally, these results emphasize the need for prospective studies to determine the potential beneficial effects of sedentary behavior reduction strategies on long-term clinical outcomes in this population.”

Takeaway Points

  1. Researchers conducted a cross-sectional study to test the hypothesis that there would be an association between reduced kidney function and a marked increase in sedentary time, as measured by accelerometry.
  2. Patients with estimated glomerular filtration rates (eGFRs) of <45 mL/min/1.73 m2 had more than a 4-fold higher likelihood of being sedentary compared with those with eGFRs of >60 mL/min/1.73 m2.
  3. In the chronic kidney disease subgroup, there was an association between greater sedentary time and diabetes and arthritis.