Reference
Beddhu S, Wei G, Marcus RL, Chonchol M, Greene T. Light-intensity physical activities and mortality in the United States general population and CKD subpopulation. Clin J Am Soc Nephrol. 2015 Apr 30. [Epub ahead of print]
Design
This observational analysis of the 2003-2004 National Health and Nutrition Examination Survey (NHANES) examined the association between low-intensity and light-intensity activities with mortality.
Participants
Data were analyzed from 3,626 of the participants in NHANES who, as part of the study, had worn an accelerometer that provided reliable readings for at least 10 hours per day for at least 4 days and for whom mortality data was available. All participants were over 20 years old. Accelerometer data provided objective measurements of physical activity. Data were recorded in 1-minute increments, and physical activity was categorized as sedentary or low, light, or moderate/vigorous in intensity per 1-minute interval. Mean follow-up time was 2.86 years. Of the total, 383 participants had chronic kidney disease (CKD). There were 137 deaths over the 10,390 years of follow-up in the entire cohort (1.32 deaths/100 person-years) and 50 deaths in the CKD group (4.77 deaths/100 person-years).
Outcome Measures
Mortality data was compared to physical activity.
Key Findings
The average adult in this study spent only about 35 minutes per waking hour sitting. For each waking hour of the day, if 2 minutes of sitting were traded off for 2 minutes engaged in some light activity (eg, casual walking, housecleaning, or gardening), risk of mortality dropped by a third (hazard ratio [HR]:0.67; 95% confidence interval [CI]:0.48-0.93; P=0.02). Significant changes in mortality risk were not seen for low-intensity activities like sitting in class, studying, note-taking, or standing (HR:1.01; 95% CI:0.86-1.19; P=0.87)] or for moderate or vigorous activity like brisk walking, running, or lifting heavy weights (HR:0.80; 95% CI:0.42-1.51; P=0.46).
Practice Implications
These results should shake up the way we view exercise and the role it plays in maintaining health and dramatically shift the goals we set for our patients.
According to this study, getting up and moving about a few extra minutes each hour of the day may have a greater health payoff than exercising vigorously. Few people would guess this; we assume that the more intense our exercise regimen, the better it is for us. We also assume that a bout of intense exercise in the gym will counter the rest of the day spent sitting in our offices. We are wrong.
Instead of trying to get patients to engage in high‒energy intensity activity, simply reducing their time spent sitting may prove to be both more achievable and more effective at improving their health.
Sitting, or sedentary behavior, is clearly bad for a person’s health; lack of activity is a risk factor for obesity,1 insulin resistance,2 diabetes,3 and increased mortality in the general population.4 Degrees of physical activity are defined across a spectrum from none to intense activity using units called metabolic equivalents (METs). Technically, 1 MET is defined as the amount of oxygen consumed while at complete rest, such as sitting in a chair (1 MET=3.5 mL O2/kg/min).5 Therefore, 2 METs are twice the metabolic expenditure of sitting, 3 METs are 3 times the expenditure, and so on. Generally, sedentary activity is defined as 1.0 to 1.3 METs, moderate exercise as 3 to 6 METs, and vigorous activity as more than 6 METs.6
A randomized intervention clinical trial published in 2013 reported that increasing moderate physical activity to 175 minutes per week in 5,145 overweight or obese type 2 diabetics failed to reduce their rate of cardiovascular events.7 This current study instead considered the effect of light activity to see whether time spent in the lower MET range of the exercise spectrum might have more benefit than more intense exercise.
Even if it were more effective, trying to get Americans to engage in vigorous physical activity is difficult. Currently, most Americans do not achieve even the goal of 2.5 hours per week of moderate physical activity.8,9 Instead of trying to get patients to engage in high‒energy intensity activity, simply reducing their time spent sitting may prove to be both more achievable and more effective at improving their health. In this study, light activity certainly is more effective.
Note that this 2 minutes per hour of activity is not an absolute value. It means 2 minutes “more” each hour. If a person is already doing 8 minutes per hour of light activity, we should encourage them to increase that to 10 minutes. If it can be increased further—say, an additional 5 minutes—then even better. Our current image of vigorous exercise, with sweat dripping, heart pounding, and lungs gasping, as being so healthy might not be correct. Instead, a more accurate image may be that sitting quietly in a chair is just bad for our health.
