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Guest Post: The Evolution of Sedentary Time

April 16, 2012

Mr Epidemiology: Today, I’m welcoming Lindsay Kobayashi back to the blog. You can find out more about Lindsay at the end of this post.

How sad.

The negative health effects of sedentary behaviour are a hot topic gaining scientific and popular attention. Any Canadian reading the news should be aware that sitting is killing us – Maclean’s, the Globe and Mail, and the CBC have all recently published on the topic. Given the tsunami-like obesity epidemic that has risen over North America over the past few decades, critical investigation of our sedentary behaviour is highly warranted.

Every time I hear someone talk about how sitting is killing us, I return to the same question – If I was born 50 or 100 years earlier, would I be less sedentary than I am now? In the figure above, I’ve depicted my average 16-hour day (waking hours only). Exemplary of a big question in the sedentary behaviour research domain, I am what you would call an “active couch potato” – I spend 7-8 hours week engaged in moderate-to-vigourous exercise, yet I still spend 50% of my waking hours sitting in front the computer! What does this mean for my health? And yours too – if you are reading this, you are likely somewhat similar to me. Is this sort of sedentary behaviour a new phenomenon of the latter part of 20th and early 21st century?

An Average Day as an "Active Couch Potato"

A simple yet elegant piece of evidence for the puzzle would be if time trends in sedentary behaviour among Canadians were found to partially explain increasing population obesity rates. A starting place to look is Statistics Canada’s General Social Survey, where time use of Canadians is estimated (1,2). Between 1998 and 2010, average time spent in “passive leisure activities” (including TV, reading, etc.) decreased from 2:52 (hours and minutes) to 2:39 among men over age 15, and from 2:35 to 2:20 among women over age 15. Average time spent at work decreased from 4:32 to 4:15 among men, and increased from 2:47 to 3:00 among women. Household work increased from 2:24 to 2:29 among men and decreased from 4:03 to 3:53 among women. Sadly, no indication of intensity is available in these estimates – but, tangentially, interesting in terms of gender roles in Canada!

So, what’s in the published literature? We have evidence on time trends in physical activity and inactivity, but not so much on sedentary behaviour. Some research shows that prevalence of leisure-time physical inactivity and “sedentary” behaviour (definitions are inconsistent) has been decreasing among Canadian adults (3–5), while prevalence of inactivity at work is increasing (3). Trouble is, we can’t go back in time and objectively measure sedentary behaviour of previous generations of Canadians. Despite limitations, these findings are disconcerting, especially since it appears that exercise may not save those of us with sedentary jobs (6,7). Another pertinent question is: do genetics play a role in resistance or susceptibility to negative health effects of sedentary time, just as they do in the physical response (such as weight loss) to moderate and vigourous intensity exercise?

A Hypothetical Average Day with Sustained Light Activity but no Exercise

Returning to my original thought – the second figure, directly above, shows what I think my physical activity/sedentary profile would look like if I was if I was born in the early 20th century. My guess is I would spend more waking hours engaged in household work, likely ranging from light to moderate intensity, and would be less likely to have a job I would spend all day sitting at (i.e., I would likely be a housewife). Triathlons and sport would probably not happen. So what’s better or worse for health – the first or the second pie chart? And how would my genetics play a role in susceptibility to the ill health effects of the time I spend at various physical intensity levels? My example is only one, but it is representative of bigger questions at the population level. I’m looking forward to future work explaining the changing social nature of sedentary time among Canadians, and how we can move toward becoming a healthier society.

About the Author: Lindsay Kobayashi is a Community Health and Epidemiology MSc student at Queen’s University. Her thesis research is on lifetime physical activity and risk of molecular marker-defined breast cancer subtypes in women. She is planning to research social inequalities in cancer screening participation for her PhD beginning in September at University College London (UCL). When she’s not researching, she’s running triathlons and reading. You can follow her on Twitter at @1lindsayk

References
ResearchBlogging.org

  1. Statistics Canada. Table 1.1 Average time spent per day on various activities, for the population and participants aged 15 and over, by sex, Canada, 2010 [Internet]. General Social Survey – 2010 Overview of the Time Use of Canadians: Highlights. 2011 [cited 2012 Apr 10];Available from: http://www.statcan.gc.ca/pub/89-647-x/2011001/tbl/tbl11-eng.htm
  2. Statistics Canada. Table 1.2 Average time spent per day on various activities, for the population and participants aged 15 and over, by sex, Canada, 1998 [Internet]. General Social Survey – 2010 Overview of the Time Use of Canadians: Highlights. 2011 [cited 2012 Apr 4];Available from: http://www.statcan.gc.ca/pub/89-647-x/2011001/tbl/tbl12-eng.htm
  3. Juneau CE, & Potvin L (2010). Trends in leisure-, transport-, and work-related physical activity in Canada 1994-2005. Preventive medicine, 51 (5), 384-6 PMID: 20832417
  4. Bruce MJ, & Katzmarzyk PT (2002). Canadian population trends in leisure-time physical activity levels, 1981-1998. Canadian journal of applied physiology = Revue canadienne de physiologie appliquee, 27 (6), 681-90 PMID: 12501004
  5. Li FX, Robson PJ, Chen Y, Qiu Z, Lo Siou G, & Bryant HE (2009). Prevalence, trend, and sociodemographic association of five modifiable lifestyle risk factors for cancer in Alberta and Canada. Cancer causes & control : CCC, 20 (3), 395-407 PMID: 18998220
  6. van der Ploeg HP, Chey T, Korda RJ, Banks E, & Bauman A (2012). Sitting time and all-cause mortality risk in 222 497 Australian adults. Archives of internal medicine, 172 (6), 494-500 PMID: 22450936
  7. Finni T, Haakana P, Pesola AJ, & Pullinen T (2012). Exercise for fitness does not decrease the muscular inactivity time during normal daily life. Scandinavian journal of medicine & science in sports PMID: 22417280
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