‘The average Canadian is slightly less active than a (motionless) fire hydrant’ – Andrew Pipe

If this statement is true for the average Canadians, one wonders if it also rings true for our neighbors to the south. Such bombastic rhetoric may seem over the top, but the sitting disease is truly an epidemic of sorts. With sitting at work, sitting at home (usually watching something), or sitting during our commute, a lot of time is spent just sitting throughout the day.

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What might this mean for kidney health? Could physical activity, or lack thereof, be on the pathway to more kidney disease?

Sedentary behaviors are certainly associated with higher incidences of diabetes, hypertension, and cardiovascular disease. Moreover, the relationship could be bidirectional, since chronic kidney disease (CKD) itself and its accompanying comorbid conditions could make physical activity more difficult. Using data from the Canadian Health Measures Survey (CHMS), Glavinovic et al from the University of Manitoba explore this relationship in a recent article published in AJKD.

Though the CHMS is a cross-sectional survey, for physical activity, the questions went above and beyond what a normal survey would do. About 8,444 individuals from the overall cohort of just over 10,000 completed activity monitoring using accelerometry. They wore an Actical accelerometer over the dominant hip during the waking hours for 7 days. For analysis in this study, they were then divided into quartiles, with Q4 representing the fire hydrant group (least active, most sedentary).

Despite this meticulous assessment of the physical activity, some caveats should be considered (as the authors do point out in their discussion). The Hawthorne effect could very well apply – surely the act of measurement will change the thing that is being measured. Additionally, these accelerometers poorly capture non-weight bearing activities (eg cycling or swimming) nor do they have an inclinometer to measure change in posture.

So what did Glavinovic et al find from the CMHS?

Firstly, very few participants in the survey had CKD: only 323 patients out of the 8,444 had a GFR of < 60 mL/min/1.73 m².

Demographic Characteristics by eGFR Category. Note: Results of continuous variables presented as mean ± SEM; categorical variables, as proportions. Table 2 from Glavinovic et al, AJKD © National Kidney Foundation.

A question to keep in mind with respect to external validity here – would this study perhaps represent the ‘healthier’ CKD patients? Would ‘sicker’ CKD patients be even less active? Table 1 shows the demographics and health conditions by quartiles of physical activity, and the remarkable thing about this table is that each row is statistically significant, with most P values being <0.001.

Demographic Characteristics by Sedentary Time Quartile. Note: Results of continuous variables presented as mean ± SEM; categorical variables, as proportions. Table 1 from Glavinovic et al, AJKD © National Kidney Foundation.

Dramatic separation – sitting and not sitting – is thus a huge signal of many things, to put it mildly. For the main result, CKD is indeed strongly associated with the least active participants, Quartile 4 (the aforementioned ‘fire hydrant’ phenotype). Even when adjusted for all other variables, this association holds strong and persisted for other chronic conditions such as arthritis, diabetes, and older age.

This study represents high quality data on actual activity and its association with CKD, but also diabetes and arthritis. The causation conundrum remains, however, since it could be fatigue driving the lack of activity in CKD, and not just the lack of physical activity contributing to CKD. Trials have shown salubrious effects of increased physical activity and exercise in non-CKD populations. There are ongoing trials aimed at increasing physical activity and exercise in dialysis patients. We do still need to understand the type of physical activity that is both desirable and confers the most benefit (eg perhaps resistance is better than aerobic?) for our CKD patients. This study is a step in the right direction towards that goal.

– Post prepared by Swapnil Hiremath, AJKDBlog Contributor. Follow him @hswapnil.

To view Glavinovic et al (subscription required), please visit AJKD.org.

Title: CKD and Sedentary Time: Results From the Canadian Health Measures Survey
Authors: T. Glavinovic, T. Ferguson, P. Komenda, C. Rigatto, T.A. Duhamel, N. Tangri, and C. Bohm
DOI: 10.1053/j.ajkd.2018.03.031