Wednesday, August 17, 2011

Sitting and Health

I just wanted to gather together some of the studies I'd referenced before about the dangers of the modern sedentary lifestyle.

Summary

Our bodies were not built for life in a chair and it is no surprise that research has highlighted the danger that so much sitting poses to health. Scientists have found that time spent sitting was associated with increased risk of mortality. Those who sat “most of the time” were more likely to die during the following 12 years than those who “almost never” sat, even after controlling for age, smoking, body weight and physical activity[2]. Even if they exercised, people who sat for over 6 hours per day had a higher risk of death than those who sat for under 3 hours per day[3]. Sitting watching television for an average of 6 hours a day could shorten life-expectancy by almost 5 years[4].



1. Owen et al. British Journal of Sports Medicine 2009;43:81–83.

 Research on physical activity and health has pointed clearly to increasing the time that adults spend doing moderate to vigorous intensity activities: 30 minutes a day is generally recommended. However, recent evidence underlines the importance of also focusing on sedentary behaviours—the high volumes of time that adults spend sitting in their remaining “non-exercise” waking hours. We provide a brief overview of recent evidence for the distinct relationships between ‘too much sitting’ and biomarkers of metabolic health and, thus, with increased risk of type 2 diabetes, cardiovascular disease and other prevalent chronic health problems. Particular concerns for this new field include the challenges of changing sedentary behaviours in the context of ubiquitous environmental and social drivers of sitting time; examining the effects of interventions for reducing or breaking-up sitting time and identifying the most relevant implications for clinical and public health practice.

2. Katzmarzyk et al. Medicine and Science of Sports and Exercise 2009;41:998-105.

PURPOSE:
Although moderate-to-vigorous physical activity is related to premature mortality, the relationship between sedentary behaviors and mortality has not been fully explored and may represent a different paradigm than that associated with lack of exercise. We prospectively examined sitting time and mortality in a representative sample of 17,013 Canadians 18-90 yr of age.

METHODS:
Evaluation of daily sitting time (almost none of the time, one fourth of the time, half of the time, three fourths of the time, almost all of the time), leisure time physical activity, smoking status, and alcohol consumption was conducted at baseline. Participants were followed prospectively for an average of 12.0 yr for the ascertainment of mortality status.

RESULTS:
There were 1832 deaths (759 of cardiovascular disease (CVD) and 547 of cancer) during 204,732 person-yr of follow-up. After adjustment for potential confounders, there was a progressively higher risk of mortality across higher levels of sitting time from all causes (hazard ratios (HR): 1.00, 1.00, 1.11, 1.36, 1.54; P for trend <0.0001) and CVD (HR:1.00, 1.01, 1.22, 1.47, 1.54; P for trend <0.0001) but not cancer. Similar results were obtained when stratified by sex, age, smoking status, and body mass index. Age-adjusted all-cause mortality rates per 10,000 person-yr of follow-up were 87, 86, 105, 130, and 161 (P for trend <0.0001) in physically inactive participants and 75, 69, 76, 98, 105 (P for trend = 0.008) in active participants across sitting time categories.

CONCLUSIONS:
These data demonstrate a dose-response association between sitting time and mortality from all causes and CVD, independent of leisure time physical activity. In addition to the promotion of moderate-to-vigorous physical activity and a healthy weight, physicians should discourage sitting for extended periods.


3. Patel et al. American Journal of Epidemiology 2010;172:419-429.

 The obesity epidemic is attributed in part to reduced physical activity. Evidence supports that reducing time spent sitting, regardless of activity, may improve the metabolic consequences of obesity. Analyses were conducted in a large prospective study of US adults enrolled by the American Cancer Society to examine leisure time spent sitting and physical activity in relation to mortality. Time spent sitting and physical activity were queried by questionnaire on 53,440 men and 69,776 women who were disease free at enrollment. The authors identified 11,307 deaths in men and 7,923 deaths in women during the 14-year follow-up. After adjustment for smoking, body mass index, and other factors, time spent sitting (≥6 vs. <3 hours/day) was associated with mortality in both women (relative risk = 1.34, 95% confidence interval (CI): 1.25, 1.44) and men (relative risk = 1.17, 95% CI: 1.11, 1.24). Relative risks for sitting (≥6 hours/day) and physical activity (<24.5 metabolic equivalent (MET)-hours/week) combined were 1.94 (95% CI: 1.70, 2.20) for women and 1.48 (95% CI: 1.33, 1.65) for men, compared with those with the least time sitting and most activity. Associations were strongest for cardiovascular disease mortality. The time spent sitting was independently associated with total mortality, regardless of physical activity level. Public health messages should include both being physically active and reducing time spent sitting.


4. Veerman et al. British Journal of Sports Medicine 2011; doi:10.1136/bjsm.2011.085662.

Background Prolonged television (TV) viewing time is unfavourably associated with mortality outcomes, particularly for cardiovascular disease, but the impact on life expectancy has not been quantified. The authors estimate the extent to which TV viewing time reduces life expectancy in Australia, 2008.

Methods The authors constructed a life table model that incorporates a previously reported mortality risk associated with TV time. Data were from the Australian Bureau of Statistics and the Australian Diabetes, Obesity and Lifestyle Study, a national population-based observational survey that started in 1999–2000. The authors modelled impacts of changes in population average TV viewing time on life expectancy at birth.

Results The amount of TV viewed in Australia in 2008 reduced life expectancy at birth by 1.8 years (95% uncertainty interval (UI): 8.4 days to 3.7 years) for men and 1.5 years (95% UI: 6.8 days to 3.1 years) for women. Compared with persons who watch no TV, those who spend a lifetime average of 6 h/day watching TV can expect to live 4.8 years (95% UI: 11 days to 10.4 years) less. On average, every single hour of TV viewed after the age of 25 reduces the viewer's life expectancy by 21.8 (95% UI: 0.3–44.7) min. This study is limited by the low precision with which the relationship between TV viewing time and mortality is currently known.

Conclusions TV viewing time may be associated with a loss of life that is comparable to other major chronic disease risk factors such as physical inactivity and obesity.

3 comments:

Anonymous said...

I think these studies are best seen as raising some interesting questions as opposed to pointing to conclusions.

I would like to see a proposed mechanism for sitting-->death? Are we to believe that lying down for 8 or more hours a day is essential, but that sitting will send us to an early grave? The possibility can't be ruled out, but I think we need more evidence than correlation among self-reported data (and some of it rather subjective data at that).

I also question whether all confounding factors have really been accounted for. For example, it seems quite likely that more of the non-sitting would have occurred outdoors. I wonder if vitamin D levels were the same among the sitters and non-sitters. Or does it make a difference whether you sit down to play chess or to watch American Idol?

antispirit said...

I try to stand most of the day at work. I do it mostly because it makes me feel more alert and happy. I will not be convinced of any other benefit until I see an interventional study (more than one?). How they could pull that off, I don't know. I'm not sure how you can "placebo sit". But I'll leave that to smarter people.

Interval training said...

Great blog, and great read! Looking forward to reading more.