Too much sitting may increase cancer risk

Lazy boyYou’ve heard it here more than once: sitting too much is bad for you. Unfortunately, much of our everyday life is comprised of prolonged sitting – from your car, to your desk, to your dining table, to your couch. There’s just no escaping the temptation to sit. Sometimes, despite your best efforts, sitting is the only socially acceptable option. (Ever tried standing in a movie theatre or at dinner in a restaurant? This guy has)

Sitting too much increases your risk of a variety of diseases and early mortality even if you are at a healthy weight and you regularly exercise. For instance, as Travis previously summarized, a “longitudinal study from Australia reports that each hour of daily television viewing is associated with an 11% increase in the risk of all-cause mortality regardless of age, sex, waist circumference, and physical activity level.”

Some have gone as far to suggest that sitting is the new smoking. How is that for an ominous metaphor?

In case you needed more proof that excess sitting is, in fact, killing you – here it is, courtesy of a new study published in the Journal of the National Cancer Institute: too much sitting is also associated with an increased risk of certain cancers.

In the study, the authors analyzed data from 43 individual studies including a total of 68 936 cancer cases (a study or studies, or a meta-analysis in science-geek parlance). Across all these studies they compared the risk of a specific cancer in the most versus the least sedentary group.

Comparing the highest levels of sedentary behavior to the lowest, the study observed a significantly higher risk for three types of cancers of the colon, endometrium, and lung.

Specifically, for each 2-hr increase in daily sitting time, the risk for colon cancer, endometrial cancer, and lung cancer, increased by 8%, 10%, and 6%, respectively.

Similar observations were reported for the specific behaviours of TV viewing time and occupational sitting time as well as total sitting time.

As has been described in other similar studies, these associations were true regardless of how much individuals exercised. In other words, not only do we all need to try to be physically active, we have to ensure we’re not falling into the category of an active couch-potato. That is, one who exercises for an hour a day, but spends the rest of his/her time with their butt firmly planted in a chair or couch.

As always, we have to keep in mind the limitations of this type of study. One of the first lessons we all learn in an entry statistics class is that correlation does not equal causation. An increased risk of certain cancers with increased idle time has been observed consistently across many studies, but this does not definitively prove that sitting causes cancer.

Nevertheless, limited lab studies in humans and animals have provided some insights into the mechanisms by which this might happen. The authors of this paper suggest a number of ways in which sitting may lead to cancer – with the mechanism potentially differing based on the type of cancer in discussion. At this point, however, the picture remains blurry.

What is less unclear is the fact that we’d all likely do ourselves a favour by spending less time on our ischial tuberosities (sitting bones).


Daniela Schmid, Michael F. Leitzmann. Television Viewing and Time Spent Sedentary in Relation to Cancer Risk: A Meta-analysis. Journal of National Cancer Institute. 2014. DOI:10.1093/jnci/dju098

Category: News, Obesity Research, Peer Reviewed Research, Physical Activity, Sedentary Behaviour | 1 Comment

New Study: High Levels of Air Pollution Associated with Lower Levels of Physical Activity

Today’s post comes from Dr Jennifer D Roberts.  You can find more on Jennifer at the bottom of this post.

Physical inactivity, ambient air pollution and obesity are modifiable risk factors for non-communicable diseases, with the first accounting for more than three million annual deaths.  Recently, we identified an association between increased ambient air pollution, specifically particulate matter 2.5 (PM2.5), and reduced leisure-time physical activity within the U.SNumerous scientific studies have linked PM2.5 exposure to a variety of health problems including irregular heartbeat, aggravated asthma, and premature death.  However, many of these studies have illustrated these effects in a resting, inactive state, or among elite athletes and the data examining the effects of poor air quality among larger individuals or in real-world physically active settings are meager.

Figure 1. Pollution in the USA (Roberts et al., PLOS ONE)

Figure 1. PM 2.5 Air pollution in the USA.  Darker blue represents higher levels of pollution. (Roberts et al., PLOS ONE)

Figure 2

Figure 2. Prevalence of leisure-time physical inactivity. Darker orange represents higher level of physical inactivity.


This research found that the highest concentrations of PM2.5 were in the upper Atlantic, Midwest, and the South, along with a small cluster in Southern California (Figure 1).  By comparison, Figure 2 shows the unweighted prevalence of leisure-time physical inactivity in U.S. counties.  Both maps illustrate higher levels of PM2.5 and leisure-time physical inactivity in the South and Midwest.  

Our study findings were compelling because they indicated that the magnitude of this inverse association between air pollution and physical activity was more pronounced among the normal or healthy weight, as opposed to overweight or obese individuals.  Specifically, for these leaner individuals, we estimated a 16–35% relative increase in the odds of leisure-time physical inactivity per exposure class increase of PM2.5 after controlling for several variables, such as age, sex, race, income, seasonality, and urbanization (Figure 3).  We recently published our findings in PLOS ONE this past March (DOI: 10.1371/journal.pone.0090143).

Odds of Physical Inactivity By Pollution Exposure and Body Weight.  Data are adjusted for adjusted for age, sex, race/ethnicity, education, annual income, marital status, seasonality, geographic region, general health status, smoking, disability, asthma, urbanization, and the other air pollutants. (Robertson et al., PLOS ONE)

Figure 3. Odds of Physical Inactivity By  PM 2.5 Air Pollution Exposure and Body Weight. Data are adjusted for age, sex, race/ethnicity, education, annual income, marital status, seasonality, geographic region, general health status, smoking, disability, asthma, urbanization, and the other air pollutants. (Robertson et al., PLOS ONE)

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Category: Guest Post, Obesity Research, Peer Reviewed Research, Physical Activity | Tagged | 2 Comments

Sorry everyone – LeBron’s muscle cramps were NOT caused by dehydration or salt loss

LeBron James (Image by Steve Jurvetson)

LeBron James (Image by Steve Jurvetson)

Last week during game one of the NBA Finals between the Miami Heat and San Antonio Spurs, the air conditioning system in the AT&T Center wasn’t working properly. As a result, the normally cool arena was a sweltering 90 degrees fahrenheit (~30 degrees Celsius). Miami’s LeBron James suffered a debilitating bout of muscle cramps, and had to leave the game. LeBron James is the single most dominant basketball player of his generation. So when he misses a significant portion of one of the most important games of the year, it is a Big Deal. Miami went on to lose the game 110 to 95.

Almost immediately, commentators went into a frenzy discussing how the heat and related dehydration/salt loss caused King James’ cramps (in the above video, the heat is mentioned several times within seconds of James cramping up). This article from ESPN, was pretty typical of the coverage that I saw online:

Miami Heat forward LeBron James was forced to exit early from Game 1 of the NBA Finals because of severe leg cramping caused by extremely warm temperatures after the air conditioning in the arena malfunctioned.

Or take this article, titled “Why heat cramps crushed LeBron”:

“In a regular game, professional athletes lose an extraordinary amount of fluid and electrolytes,” says Dr Michael Bergeron, executive director of the Sanford Sports Science Institute. “Playing in hot and humid conditions can push a player’s fluid and electrolyte loss to a dangerous level.” As dehydration sets in, subtle twitches or cramping can progressively turn into painful muscle spasms.

The prevailing wisdom being that the heat caused dehydration and/or electrolyte loss, which caused his muscle cramps. The analysis has been fast and furious (the classiest was Gatorade pointing out on Twitter that people who consume their sugar water sports drink can “take the heat” – LeBron is sponsored by Powerade), but most of it seems to miss a crucially important point: research suggests that exercise-related muscle cramps are not caused by dehydration or electrolyte loss (I was surprised that even articles explaining “the science of muscle cramps” largely sidestepped the issue).

The real explanation is way less sexy: exercise induced muscle cramps are caused by plain old fatigue.

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Category: News, Peer Reviewed Research, Physical Activity | Tagged | 8 Comments

Is it safe to exercise when pregnant?

Not my wife (Image by seandreilinger)

Not my wife (Image by seandreilinger)

The short answer  is yes – it is absolutely safe to exercise while pregnant.  It is also very beneficial.  There are a few situations that you want to avoid (e.g. maximal exercise, overheating, etc), although I can’t imagine many pregnant women choosing to engage in those types of exercise anyway.

These and other topics are discussed today in the latest installment of the Obesity Panacea podcast.  This time I am joined by my friend and colleague Dr Zach Ferraro.  Zach’s research interests include physical activity and weight management during pregnancy.  The impetus for this podcast was the fact that my wife is pregnant (!!!) with our first baby, and we were both curious about how physically active she could/should be while pregnant.  In the podcast Zach and I talk about some of the questions that Daun and I had, the types of activities that are recommended for pregnant women, and also how to recognize if you’re doing too much.

Daun and I have always been very physically active (we met on a varsity cross country team), she even moreso than me.  She’s cycled across Canada, can portage a canoe solo (I find this far more impressive than she does), etc. So it was really important for us to know what types of exercise are safe/potentially unsafe for a pregnant woman.  On that note, I’d like to remind people that  Zach is not a physician, so he was only able to give general info, rather than specific info for Daun (which I imagine will also make the podcast more useful for others).

Let me be the first to point out the irony of 2 men discussing pregnancy – my wife had hoped to join us for the podcast, but wasn’t feeling well the night that we did the podcast (we did the podcast at the end of the first trimester, during what was probably the worst week of the whole pregnancy… we’re now into the 3rd trimester and she is feeling much better). But many of the topics we discuss were ones that she had asked us to include in the podcast.

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Category: Interview, nutrition, Obesity Research, Physical Activity, Podcast | Tagged | 2 Comments

Cycling is safer than you think (but not as safe as it should be)

Image by Wolfgang Staudt

Last week there was a tragic and fatal bike accident here in Halifax.  As avid road cyclists, these sorts of accidents always hit home for my wife and I.  Even moreso in this case, as the cyclist’s description (an elementary-school teacher and cycling enthusiast in her early 30′s) is also an apt description for my wife.

Although the cause of the crash is still unclear (the cyclist was hit by a truck turning right, although no word yet on whether anyone was at fault), these sorts of accidents drive home the fact that riding a bike can, at times, be a dangerous activity.  And so, I thought this would be a good time to revisit just how dangerous cycling is, when compared to other modes of transportation.

The most useful information that I’ve encountered on this topic is from a paper in Environmental Health Perspectives which examines whether the benefits of increased cycling (increased physical activity) outweigh the risks (both in terms of accidents and exposure to pollutants for individual cyclists).  To calculate these numbers, the authors examine changes in mortality at both the population level, and for individual cyclists, if 12.5% of current short car trips in the Netherlands were to be performed by cycling instead.

So, what did they find?

The authors report that for most adults, the risk of death when cycling is about 4.3x higher than if the same trip were being made by car (YIKES!). However, we’ve got to remember that commuters not only pose a risk to themselves – they also post a risk to other road users.  And if you’re going to be hit by a vehicle, a Cervelo is going to do you a lot less harm than a Corolla!  There is a reason why you don’t hear about out-of-control cyclists taking out a swath of pedestrians.  So with an increase in the number of trips made by bike, the increased mortality among cyclists due to traffic accidents is offset by the reduced mortality among the general population who would be less likely to be run over crossing the street (interestingly, if it were high risk young drivers who were to switch from driving to cycling, it would actually save lives!).

Now while the risk of being in an accident is higher for cyclists, it must be remembered that they are also likely to be getting increased levels of health promoting physical activity, and substantially reducing their volume of sedentary time.  In fact, the risk of death due to physical inactivity among active commuters is estimated to be 10-50% lower than in non-active commuters – a pretty substantial health benefit!

So will cycling to work make your life longer or shorter?  On average, the risk due to car accidents will reduce your life expectancy by just 5-9 days.   Being exposed to air pollution during your commute could cost you another 8-40 days.  But the physical activity in your commute would actually increase your life expectancy by up to 14 months! Overall, the health benefits of active commuting by bike are 9 times greater than the risks!

Lest that you think that this is only true in the cycling utopia that is the Netherlands, similar studies have also suggested that the benefits of cycling outweigh the dangers in countries ranging from Spain to India and the UK.  Just this week it was reported that after 8.75 million trips covering more than 14 million miles, there has yet to be a single fatality associated with the new Citi bike-share program in New York City (there have been only 100 reported accidents so far, and only 25 of those warranted a trip to the emergency room).  When you consider that the people most likely to use a bike-share program are tourists and other individuals who don’t spend a lot of time on a bike, those results are very heartening.  Especially when you take into account the many failings of urban cycling in North America (see videos below).

What’s the take-home message?

Cycling is obviously more dangerous that it should be, something which needs desperately to be addressed.  But if you decide to commute by bicycle on a regular basis, you are far more likely to improve your health and prolong your life via increased physical activity than you are to shorten your life by getting involved in an accident.  It is interesting and extremely important to note that the number of cyclists on the road is inversely related to the number of car/bike collisions  – so the more of us that get out on the roads, the less likely we are to get in an accident.

And if you do choose to cycle more regularly (which I definitely think you should!), please wear a helmet and obey traffic laws – especially stop signs.  Those two factors alone will go a long way to preventing some cycling related deaths.

Today’s post is an update from a post published on Obesity Panacea in September of 2010.


Category: News | 6 Comments

Over 1 in 3 adults worldwide are now overweight or obese


According to a brand new study, the global prevalence of obesity is on the rise – and this seems to be true of men and women, adults and children, and those in developed and developing countries. But there are some interesting differences according to country, age, and gender and even some potentially positive news.

The results come from a massive study just published in the journal Lancet assessing the worldwide change in the prevalence of people who are overweight or obese (BMI≥25kg/m2). By massive, I’m referring to the fact that this study used data from a whopping 1769 individual studies from 183 countries. That alone is an impressive feat.

Let’s dig a bit deeper into the study findings, shall we?

Globally, between 1980 and 2013, the proportion of men who were overweight or obese increased from 28.8% to 36.9%, while the proportion of women in this category increased from 29.8% to 38.0%.

Across time, the prevalence of overweight/obesity was higher in developed than in developing countries across all ages.

For instance, in 2013, the US accounted for 13% of all obese people worldwide! This is a tremendous statistic given that the US accounts for approximately 4.4% of the world’s population.

Interestingly, more men than women were overweight and obese in developed countries like the US and Canada, whereas the opposite was true in developing countries (overweight and obesity was more prevalent in women).

The rates of overweight and obesity peaked in men at about 55 years of age; meanwhile the peak age in women was approximately 60 years.

And adults weren’t the only ones putting on the pounds; rates of excess weight in children and adolescents also increased. Between 1980 and 2013 in developed countries, the prevalence of overweight and obesity has increased from 16.9% to 23.8% among boys and from 16.2% to 22.6% among girls.

While the greatest increase in obesity prevalence occurred between 1992 and 2002, this trend has tapered down in the past decade, particularly in developed countries.

That is, as a species, we’re still getting fatter, albeit at a slower pace.

This was the good news I was referring to above. Not the most encouraging, but given the barrage of negative news regarding the obesity pandemic, I’ll take what I can get.

Excess weight has previously been estimated to cause 3.4 million global deaths per year, and it has been postulated that, at least in the US, the rise in obesity could actually result in shorter life expectancy for future generations – thereby reversing the temporal trend of increasing life expectancy over time. The fact that a growing proportion of the global population is crossing the threshold into excess weight suggests that this daunting prediction may become true.

The exact cause of this global weight increase is anyone’s guess. The authors of this paper suggest the usual suspects: increased caloric intake, changes in the composition of diet, decreased levels of physical activity. Then they promptly throw their hands up.

Due to the continued westernization of many developing countries across the globe, no one should be surprised if the global rates of obesity continue to climb into the future. The slight plateauing in the rise of obesity in developed countries may indicate that some of the strategies enacted over the past decade are actually having some impact. Hopefully, we can help developing countries launch similar public health strategies and turn the tide before obesity rates in these countries mirror those of more developed (and chubbier) counterparts.

Interesting fact: The research was funded by the Bill & Melinda Gates Foundation.


Reference: Ng et al. Global, regional, and national prevalence of overweight and obesity in children and adults during 1980–2013: a systematic analysis for the Global Burden of Disease Study 2013. (2014) The Lancet.

Category: News | 12 Comments