座る時間が長いと、運動量と関係なく死亡と関連

●2012年発行のJAMA = The Journal of the American Medical Association = によると、45歳以上の被験者約22万人から得られたデータから、座る時間と死亡との関連が明らかとなった。

●一日に座る時間を４つのカテゴリ（0-3, 4-7, 8-10, 11〜 時間）に分けて調査をしたところ、カテゴリが一つ上に上がるたびに、11%総死亡率が上がるという結果が出た（ハザード比1.11，95%CI：1.08-1.15）

●ハザード比（95%信頼区間）はそれぞれの座位時間カテゴリにおいて，1.0（N/A），1.02（0.95-1.09），1.15（1.06-1.25），1.40（1.27-1.55）であった。

●また，この座位による死亡率は性別，年齢，運動量，BMI，心臓病・糖尿病の有無とは無関係に増加することが分かった。

●座位による人口寄与割合は6.9%であり，これは死因の6.9%が座位によるものであることを示唆している。

●座位時間を減らすこと（特に一日8時間以下）と，適切な運動を行う事はそれぞれ死亡率を減少させることが分かった。

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Sitting Time and All-Cause Mortality Risk in 222 497 Australian Adults

JAMA.2012;172(6):494-500. doi:10.1001/archinternmed.2011.2174. (Published 2012)

Abstract

Background Prolonged sitting is considered detrimental to health, but evidence regarding the independent relationship of total sitting time with all-cause mortality is limited. This study aimed to determine the independent relationship of sitting time with all-cause mortality. Methods We linked prospective questionnaire data from 222 497 individuals 45 years or older from the 45 and Up Study to mortality data from the New South Wales Registry of Births, Deaths, and Marriages (Australia) from February 1, 2006, through December 31, 2010. Cox proportional hazards models examined all-cause mortality in relation to sitting time, adjusting for potential confounders that included sex, age, education, urban/rural residence, physical activity, body mass index, smoking status, self-rated health, and disability. Results During 621 695 person-years of follow-up (mean follow-up, 2.8 years), 5405 deaths were registered. All-cause mortality hazard ratios were 1.02 (95% CI, 0.95-1.09), 1.15 (1.06-1.25), and 1.40 (1.27-1.55) for 4 to less than 8, 8 to less than 11, and 11 or more h/d of sitting, respectively, compared with less than 4 h/d, adjusting for physical activity and other confounders. The population-attributable fraction for sitting was 6.9%. The association between sitting and all-cause mortality appeared consistent across the sexes, age groups, body mass index categories, and physical activity levels and across healthy participants compared with participants with preexisting cardiovascular disease or diabetes mellitus. Conclusions Prolonged sitting is a risk factor for all-cause mortality, independent of physical activity. Public health programs should focus on reducing sitting time in addition to increasing physical activity levels.