Time spent in sedentary behaviors: United States, 2003-2004.

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Context. Time spent in sedentary behaviors (SB) has been linked to many adverse health outcomes, including cancer, but the amount of time spent in these behaviors by the United States population (US) is unknown. Objective. To describe the amount of time spent in overall sedentary behaviors in the US, by age, gender, and racial/ethnic group. Methods. Participants in the National Health and Nutrition Examination Survey (NHANES) 2003-2004 (age 6+ yrs) were asked to wear an Actigraph activity monitor for seven consecutive days during waking hours. SB was determined as the amount of monitor wear time spent below 100 activity counts/min, an activity pattern consistent with sitting, reclining, or lying down. Estimates of SB were summarized as a proportion of monitor wear time (%) and duration (hrs/d). Results. Among the 6,308 participants with at least one 10 hour day of monitor wear, the average number of days and hrs/d of monitor wear was 5.0 (SD=1.9) d and 13.9 (SD=1.9) hrs/d, respectively. Children (6 to 11 yrs) were the least sedentary group in the US (43%; 6.1 hrs/d), but time spent in SB increased by about 2.0 hrs/d by late adolescence (16 to 19 yrs, 58%; 8.0 hrs/d). There was a significant age-by-gender interaction in youth (6 to 19 yrs). While females were more sedentary than males throughout youth (0.42 hrs/d, p < 0.01), they had a larger increase in SB between childhood (6 to 11 yrs) and early adolescence (12-15 yrs) than males (1.57 vs. 1.39 hrs/d, respectively). White (50%; 6.9 hrs/d) and Mexican American youth (50%; 6.8 hrs/d) were the most sedentary, while Blacks were slightly less sedentary (49%; 6.7 hrs/d, p < 0.01). Young adults (20-39 yrs: 53%; 7.4 hrs/d) were less sedentary than older adolescents, but time spent in SB increased significantly after age 40. Older adults (60+ yrs) were the most sedentary group in the population (63%; 8.9 hrs/d). In contrast to youth, adult males were more sedentary than females (0.13 hrs/d, p = 0.03), and males experienced a larger increase in SB than females between early (20-39 yrs) and older adulthood (60+ yrs: 1.81 vs. 1.08 hrs/d, respectively). Mexican American adults (51%; 7.2 hrs/d) were less sedentary (p < 0.01) than all others, while White (57%; 7.7 hrs/d) and Black adults (57%; 7.6 hrs/d) were similarly sedentary. Black and White females spent the same amount of time in SB (57%; 7.9 hrs/d). Conclusion. These data provide the first direct measure of the amount of time spent in SB by the US population. Older adolescents (16 to 19 yrs) and adults 60+ yrs spent 8 to 9 hrs/d, or about 60% of their waking time, in sedentary pursuits, and these two groups were the most sedentary in the US. In youth, females were more sedentary than males, but this pattern tended to be reversed in adulthood. Mexican American adults were significantly less sedentary than other US adults. Efforts to reduce the substantial amount of time spent in SB each day may be an important strategy in the effort to increase overall physical activity levels in the US population.