In case you haven’t heard, tobacco smoking is very bad for your health. In fact, it is extremely dangerous. It is associated with an astoundingly morbid gallery of adverse consequences, including a quadrupling of cardiovascular disease risk, a quadrupling of stroke risk, at least a dozen-fold increase in lung cancer risk, an increased risk of respiratory conditions such as emphysema and bronchitis, as well as higher levels of infertility, reduced bone density, and even gangrene. In addition to cancer of the lungs, smoking contributes to the onset of cancers of the kidney, larynx, oesophegus, mouth, stomach, bladder, and uterus, making it one of the most cancerous of all human activities. The US Center for Disease Control reckon that smoking kills more Americans each year than HIV/AIDS, illegal drug use, alcohol use, motor vehicle injuries, suicides, and murders combined. But, now, the Daily Mail is telling us that research shows you probably engage in an even more dangerous habit. You — yes, YOU — are very probably engaging in it right now, thereby hastening the arrival of your own imminent death. And what is that you are doing that is so very deadly? Well, you’re going to be surprised. It might even make you fall off your chair. Because it is… sitting. As in “sitting down“. Yes, according to the Daily Mail this week, “Sitting can be more dangerous than smoking“.

Given that the vast majority of our species spends quite a lot of time sitting down, this is quite bad news for the human race in general. And so it was with some discernible relish that the ever fearful Daily Mail reported the story. They even carried quotes from a victim of this devastating blight, someone who sat but who lived to tell the tale. But guess what? It turns out that the Daily Mail got it wrong (and the quoted victim wasn’t best pleased). Now, who’d have thought that possible?

At first glance, the overall news story relates to a very valid point that sedentary lifestyles can be bad for people’s health. For one thing, they relate to obesity, which is itself extremely unhealthy (although not as dangerous as smoking). However, this particular news story emerges from a new research study published in the Journal of the American College of Cardiology, in which the authors claim that prolonged sitting in front of televisions or computer screens is associated with adverse outcomes irrespective of your body mass index and irrespective of how much physical activity you engage in at other times of the day. In other words, they are not talking about an obesity mechanism.

The researchers examined data from a sample of over 4,500 Scottish adults across a four-year period. They found that people who sat for more than 4 hours per day suffered 45% more all-cause mortality (i.e., death from anything) and 125% more CVD events (i.e., incidents of cardiovascular disease) when compared to those who sat for less than 2 hours per day. Statistically, this association was independent of the effects of other risk factors, such as gender, smoking, BMI, and physical activity. In support of the link, blood tests suggested that proteins associated with inflammation were possibly involved in the disease onsets observed.

All such studies can be critiqued on methodological grounds, although the present one had several strengths (including a rigorous follow-up protocol and the inclusion of bioassay tests). One inevitable weakness is that measures of sitting time were based on unverified self-reports. Even though the study is prospective, there is a risk that these self-reports reflected a degree of post hoc rationalization, especially among those respondents who were physically unfit to begin with. Relatedly, as in other similar study designs, the statistical model seems to assume that daily sitting time remained unchanged over the four-year period, even though it is likely that a significant subset of any group of adults can be expected to alter their behaviours across four mid-life years, especially when bombarded by public health campaigns demanding that they take more exercise. And finally, while the overall study sample was large (4,500+), the actual numbers succumbing to sitting-related all-cause mortality or CVD events are extremely small (i.e., 5 and 7 cases, respectively). Even though statistical significance can be established from them, it is difficult to be confident that such tiny numbers present an evidence base from which we can produce sound generalizations about the human population as a whole. In other words, while the evidence is important, the study requires at least a couple of replications in order to support its case. But, as these things go, it is still a pretty decent study.

One thing we can conclude, however, is that the study does not support the claim that “sitting is more dangerous than smoking“, whatever the talking heads might say. Firstly, while the study data imply that sitting led to 125% more CVD events, this seems very modest when compared to the fact that tobacco smoking typically leads to up to 400% more CVD events. Secondly, while sitting appears to have led to 45% more all-cause mortality in the present study, smoking typically leads to in excess of 100% more all-cause mortality in adult samples. And these comparisons don’t take into account the several other illnesses and disabilities attributable to smoking (and thus, to its “dangerousness”), but which are unlikely to be linked with sitting at all (things like like infertility and gangrene).

The claim that “sitting is more dangerous than smoking” may encourage people to take more exercise, which is a good thing. However, as it is inaccurate, the claim is itself actually quite dangerous. This is because its very inaccuracy may encourage people to underestimate the true dangers of smoking. If the general public come to believe that smoking is in fact safer than sitting, then it is pretty inevitable that concerned smokers will simply end up smoking more and that a greater number of curious non-smokers will eventually take up smoking.

However, poor conclusions based on relative risk statistics were not the only problem with the Daily Mail piece. Notably, one of the people they quoted  — one Paul Golin from New York — was so unhappy with how his comments were presented that he posted a complaint to the Daily Mail’s website. The Mail had described his testimony as follows:

Paul Golin told CBS he was sitting up to eight hours a day until he had a health scare which he believes was largely brought on by sitting down all day.

However, Golin himself had a different impression. In his post, viewable on the Comments section at the end of the article, he states:

At no point in the CBS piece – or ever in my life – have I said that I believe my “health scare…was largely brought on by sitting down all day.” In fact, in the piece I specifically mention a family history. Please correct this inaccuracy, lest it be permanently attached to my name on the never-erasable record that is the Internet. I’m really not a hard person to reach; a 3-second Google search will get you my email address. But if you’re just going to copy someone else’s story and call it “journalism” rather than actually talking to people yourself, at least try to copy correctly.

Stirring words indeed! Really gets the blood pumping.

In fact, I think I need to go and sit down…