Sedentary living seems to take its greatest toll among the frailest older adults, but regular activity may offset those effects, a study published online August 21 in CMAJ has found.
The mortality risk associated with sedentary behavior, defined as hours spent sitting, was significantly greater for the frailest individuals than for their counterparts who were not as frail, Olga Theou, PhD, from the Division of Geriatric Medicine, Dalhousie University, Halifax, Nova Scotia, and colleagues write.
However, sedentary time "was associated with a higher risk for death only in vulnerable or frail people who did not meet the weekly recommendation for 2.5 hours of moderate physical activity," Dr Theou said in a news release.
For people who met that activity requirement and for those who reported engaging in just 10 minutes of moderate to vigorous activity during the previous 30 days, there was no significant interaction between frailty and sedentary behavior, and sedentary time was not associated with mortality.
Dr Theou urged physicians to "stress the harms of inactivity with all patients, similar to the harms of smoking, to encourage movement. Even something as simple as getting up and walking around the house with a walker or cane can benefit frailer people."
Calculating Frailty
The prospective study used data from the 2003 to 2004 and 2005 to 2006 cohorts of the US National Health and Nutrition Examination Survey. The researchers included 3141 participants who were at least 50 years of age at baseline, had a valid score on a 46-item frailty index, and wore an activity monitor (accelerometer) for at least 10 hours a day on 4 separate days. They were followed until their death or the conclusion of the study on December 31, 2011 (mean, 6.5 years; standard deviation, 1.6 years).
Participants were divided into four groups according to the frailty index score: 0.1 or less (least frail; n = 766), 0.1 to 0.2 or less (n = 1121), 0.2 to 0.3 or less (n = 681), and more than 0.3 (most frail; n = 573).
The researchers defined low sedentary behavior as sitting for fewer than 7 hours per day during waking hours, intermediate as sitting for 7 to 10 hours per day, and high as sitting for more than 10 hours per day. In addition, the subjects reported if they had engaged in 2.5 hours per week of moderate to vigorous physical activity, or in any vigorous activity for at least 10 minutes during the last 30 days.
The researchers analyzed the relationship among frailty, activity level, and mortality according to regression models that controlled for a long list of covariables, including age, sex, body mass index, and smoking status, among others.
Frailty, Activity, and Mortality
There were 550 deaths during the study period. Mortality increased with frailty, from 42 in the least frail group (weighted percentage dead at follow-up, 2.8) to 215 among the most frail (weighted percentage dead at follow-up, 35.3; P < .001).
Among the least frail, mortality did not vary appreciably according to low, intermediate, or high sedentary behavior: the weighted percentages of those dead at follow-up were 2.9, 2.8, and 2.4, respectively. However, among the frailest individuals, the respective weighted percentages were 20.4, 30.1, and 49.6, respectively (P < .001).
On Cox regression analysis, "we found that for those who met the moderate-to-vigorous physical activity requirements and for those who reported vigorous physical activity, there was no significant interaction between frailty and sedentary behaviour, and sedentary time was not associated with mortality," the authors write.
"Thus, among people who are inactive and vulnerable or frail, sitting time increases mortality risk, but among those who are nonfrail or active, sitting time does not affect the risk of mortality," they add.
Among the study limitations was that the researchers were missing activity monitor data for nearly one third of the participants, "and these participants seemed to have higher levels of frailty," the authors write. The missing data reduced the sample size substantially, especially among the frailest group, they explain.
"Future studies will need to examine the effect of sedentary behaviours on people with higher levels of frailty using other data sets." Other limitations included a lack of information on alcohol consumption and income within the cohort, and the possibility of overestimating sedentary time among the frailer individuals.
These findings show that "the effect of sedentary behaviours on mortality differs across levels of frailty among people who are physically inactive, with people who are most frail experiencing the greatest impact," they conclude. Emphasizing the drawbacks of sedentary behavior, as well as the benefits of exercise, "is an important public health message that should be part of a larger promotion of the importance of healthy lifestyle behaviors."
Dr Rockwood reports being a founder and director of DGI Clinical Inc, attended a Roche advisory board meeting regarding outcome measurement for Alzheimer disease, and has received speaker's fees from Nutricia. The remaining authors have disclosed no relevant financial relationships.
CMAJ. Published online August 21, 2017. Full text
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