Continued sedentariness, change in sitting time, and mortality in older adults

Prolonged sitting time (ST) is associated with higher mortality. However, previous studies used only a single measure of ST at baseline, so they could not directly assess the effect of continued exposure to high ST, or of changes in ST, on mortality. We prospectively assessed the association of continued sedentariness and of changes in ST for 2 yr with subsequent long-term all-cause mortality.

This study was based on a prospective cohort of 2635 persons representative of the Spanish population 60 yr and older. ST was self-reported in 2001 and 2003. The median of ST was used as the cutoff to define excessive ST. Individuals were classified as consistently sedentary (> median in 2001 and 2003), newly sedentary (≤ median in 2001 and > median in 2003), formerly sedentary (> median in 2001 and ≤ median in 2003), and consistently nonsedentary (≤ median in 2001 and 2003). The association of ST in the period 2001-2003 with all-cause mortality from 2003 through 2011 was assessed with Cox regression and adjusted for the main confounders, including physical activity.

Among the study participants, 846 died between 2003 and 2011. Compared with persons who were consistently sedentary, the hazard ratios (95% confidence interval) for mortality were 0.91 (0.76-1.10) in those who were newly sedentary, 0.86 (0.70-1.05) in formerly sedentary individuals, and 0.75 (0.62-0.90) in those who remained consistently nonsedentary. The results were similar across strata defined according to obesity, morbidity, functional limitations, or meeting recommendations for physical activity.

Compared with older adults who were consistently sedentary during 2 yr, consistently nonsedentary individuals showed reduced all-cause mortality. Individuals who changed ST experienced an intermediate reduction in mortality.