There are an estimated 15.5 million adults with stage 3 chronic kidney disease (CKD) while only about 600,000 patients have end-stage renal disease (ESRD) in the United States. This is because most of the people with CKD die before they reach ESRD. In order to decrease the high mortality in the CKD population, the "non-renal" issues that contribute to increased morbidity and mortality in this population need to be addressed.
Relevance of sedentary behavior in CKD: Prolonged sitting time (as assessed by a questionnaire or television viewing time) was associated with lower kidney function. Total and light physical activities, measured objectively with an accelerometer were found to be positively associated with kidney function in a study of community dwelling adults. In an analysis of National Health and Nutrition Examination Survey (NHANES) data, it was noted that participants with CKD spent more than two-thirds of the awake time in sedentary activities and longer sedentary duration was associated with increased mortality. It was also noted in another study that compared to those with CKD, those on maintenance hemodialysis had 3.4 fold higher odds of being sedentary independent of demographics, co-morbidity, body size, serum C-Reactive Protein (CRP) and albumin. Thus, sedentary behavior is very common in CKD, appears to worsen with more advanced kidney failure and increases mortality risk in this population.
Feasibility of replacing sedentary activities with moderate/ vigorous physical activities: Moderate/ vigorous physical activities are less likely to be an effective replacement for sedentary activities as most Americans do not reach even the current goals and achieving the currently recommended levels of 2.5 hrs/ week of moderate/ vigorous activities would account only for 2% of the total awake time (112 hours/week). Therefore, decreasing sedentary activities must involve an increase in activities that are less intensive than moderate/ vigorous activities.
The concept of Non- Exercise Activity Thermogenesis (NEAT) and biological relevance of light intensity activity: In a overfeeding study, it was demonstrated that increase (average 336 kcal/day) in non- exercise activity thermogenesis accounted for 10-fold differences in fat storage, directly predicted resistance to fat gain and explained most of the variations in weight gain between participants. Obese persons have less non-exercise activity thermogenesis and spend an average of 2 hrs/d more in a seated position compared to lean persons. Objectively measured light activity was inversely associated with insulin resistance and cardiometabolic risk factors. Daily lifestyle activities were negatively associated with insulin resistance. Thus, replacing sedentary activities with non-exercise intensity activities of daily living could increase energy expenditure and decrease adiposity.
Determining what kind of light activity would be most beneficial in replacing sedentary activity: As standing (\~ 1.5 Metabolic Equivalents of Task (METs)) is by definition non-sedentary (i.e. not sitting or lying down), one might consider replacing sitting duration with standing duration in order to decrease sedentary behavior. However, replacing sitting duration with casual walking (2 to 2.9 METs) duration might be even more beneficial. This notion is supported by the following theoretical calculations of energy expenditure. Assuming 16 hrs/day of awake time, it was calculated that the weekly energy expenditure for a person weighing 80 kg for trade-off of 1 to 5 min/hr of sedentary activity at 1.2 METs with 1.5 METs (standing intensity activities) or 2.5 METs (casual walking intensity activities). Additional kcal/week was calculated as the difference in energy expenditure between sedentary activity and 1.5 or 2.5 METs activity using the equation Kcal/ week = (METs/hr) x weight in kg X weekly duration of the physical activity. Trade-off of 1-5 min/hr of sedentary duration with standing intensity activities duration is expected to result in additional weekly expenditure of 50-250 Kcal only. On the other hand, similar trade off of sedentary duration with casual walking intensity activities duration is expected to result in \~ 200 to 1000 Kcal/ week of additional energy expenditure. This is consistent with prior observation that increase in non-exercise activities could lead to an additional 350 Kcal/d of energy expenditure in obese individuals.
Indeed, in the NHANES analyses, it was noted that trade-off sedentary duration for light intensity (2.0 to 2.9 METs) activities but not for very light intensity (1.5 to 1.9 METs) duration was associated with significantly lower risk of mortality. Thus, replacing sedentary duration with casual walking duration could increase energy expenditure and decrease mortality in CKD.
