Monthly Archives: May 2014

What’s the real UK death toll from inactivity? Part two – how many?

In part one of this series I looked at why a lack of exercise causes premature deaths; the aim of this second part is to take a look at exactly how many people may be dying from a lack of exercise. My analysis shows that this number is very high, but it also seems that the studies that I found were underestimating the true death toll due to systematically conservative assumptions in approximations used.

 

The studies:

The HIPI model, based on Lee et al (http://www.sciencedirect.com/science/article/pii/S0140673612610319), predicts a death toll of 36,815 people a year in England, for ages 40-79, but only from coronary heart disease, colorectal cancer, breast cancer and diabetes.   This has a few conservative assumptions from my point of view: I think people start to die of inactivity from childhood (though admittedly in far lower numbers); it ignores many illnesses thought to be caused by inactivity; it uses guideline minimum amounts of exercise (150 minutes) as its baseline for active, and it doesn’t take in the whole of the UK (to allow us to compare to other equivalent statistics).

To correct the last point, we can make an approximation by taking into account the population size of England as compared to the UK, assume that the populations show similar behaviour, and arrive at an estimate of about 44,000 deaths per year in the UK. Of course, this still leaves the other issues – so let’s go back to look at the underlying study – Lee et al.

 

Lee et al quote an all-cause mortality burden of 16.9% of all deaths in the UK – with a total death toll of about 569,000 per year from the ONS, this yields 96,000 deaths per year. Again, they are assuming that active people are doing guideline amounts of exercise (i.e. over 150 minutes); they also assumed that only people over the age of 40 suffered increased mortality rates. These are two flaws which lead me to expect that this is an underestimate.

 

Whats the issue with current thinking?

Most biological systems deliver a dose response curve that looks a bit like this:

Dose-response

Basically, initially as we increase dose, you get maximal response up until a point (corresponding to about 20M/L of the drug in the graph above) where the effect of each additional dose decreases. Of course, in the case of exercise, the units of our dose will be measured in calories, minutes of activity or some measure that accounts for volume and intensity of exercise.

The above studies use models for calculating the death toll from inactivity assume that somewhere in the region of 150 minutes of exercise a week (the UK guidelines) deliver almost all of the benefit that exercise can bring. This is based on the dea that 150 minutes is at the ‘plateau’ stage of the above curve – where an increase in dose will be a small, or no, further improvement in health outcomes. I believe that this is not true, and in fact the Lee et al study in the Lancet does acknowledge this as a limitation in their estimates. A large meta-analysis (a review of available evidence) (http://ije.oxfordjournals.org/content/early/2011/09/05/ije.dyr112 ) gives an estimate of a 14% reduction of deaths at 150 minutes of exercise, and 26% – nearly double – at 300 minutes.

In fact we repeatedly find (http://www.indiana.edu/~k562/articles/role/Lee%20PA%20morbidity.pdf, http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(11)60749-6/fulltext ) that in fact, over the range of durations studied, there appears to be an linear relationship between volume of exercise and decreased mortality rates – i.e. a doubling of exercise volume doubles the protective of effect of exercise.

It feels intuitively as if there must come a point where increasing exercise volumes do not keep on reducing death rates per year – but it seems from the studies reviewed that we have not reached that point at 300 minutes, let alone 150!

We can draw a dose-response curve for exercise using currently available data, in fact someone has already done this for me using data from one study:

 

Dose-responseexercise

 

It seems moderate exercise for various activities yields about 250 calories per 30 minutes; so it looks like we’re reaching the point where the benefits of exercise start slowing at about 2,500 calories exercise per week – or 10 x 30 minutes of exercise a week – 300 minutes (warning – fast and dirty approximation!).  Note that it appears that the benefits are still accruing, albeit more slowly, at 3000 Kcal per week.

Interestingly, there seems to be no lower threshold for exercise effectiveness (so there’s no flat spot at the start of the graph) – basically any amount will start improving your health.

 

So: how many?

The evidence above seem to show that best available protection from deaths by exercise comes at more than 300 minutes of exercise a week. The studies investigated above are based on 150 minutes – which seem to show about half the level of benefit of 300 minutes.

This means that the benefit to those individuals doing less than 150 minutes can be expected to double – but this isn’t the only effect. There will be a fair chunk of the population that were considered ‘active’ under previous studies but who are doing less than 300 minutes of activity a week, and these will also benefit from doing more exercise. This leads me to suggest that the studies above are underestimating the possible protective effect of exercise by at least a factor of 2.

Applying a factor of 2 to Lee et al gives a death toll from inactivity, UK-wide, of 192,000 deaths per year. Note, this is a very fast and dirty estimate and needs further investigation, but can be expected to be a low-end estimate as I have ignored the benefit to those individuals doing between 150 and 300 minutes of exercise a week for simplicity.  I have ignored the number from the HIPI model, as it is based on the same underlying data, but is clearly ignoring a vast swathe of deaths caused by inactivity from the discrepency with the number generated by Lee et al.

This puts inactivity as a cause of death ahead of smoking (100,000 deaths per year in the UK, from here: http://ash.org.uk/files/documents/ASH_107.pdf); vastly exceeds deaths directly caused by air pollution from combustion emissions (19,000 from here: http://pubs.acs.org/doi/abs/10.1021/es2040416); and absolutely dwarfs deaths from road traffic collisions (1,754 deaths in 2012).

 

Notes of caution:

These calculations are based on correlation studies – i.e. they look at how much less likely someone who exercises at different amounts is to die than someone who’s inactive; however, as discussed in other blogs correlation does not always imply causation and there may be confounding factors around more affluent people being more likely to exercise.   As affluent people generally live longer, it may be that this is causing the apparent protective effect of exercise. However, there are also other confounders – the types of exercise participated in may expose people to greater risk of dying from other factors – e.g. air pollution from exercising outside. These confounders may cause this study to underestimate the true protective effect of exercise if, say, you were exercising in the country where this air pollution was not present in such high quantities.

 

Conclusions:

  1. It seems highly likely that any amount of exercise will improve your chance of living a long life – and the more exercise you do, the greater the benefit, until at least 300 minutes of moderate-to-intense activity per week
  2. Guideline amounts of activity are below the optimum amounts for reducing avoidable deaths according to best available data
  3. Available studies seem to be underestimating death rates from inactivity by a large amount, possibly a factor of greater than 2
  4. The reason for these underestimates is an assumption that guideline amounts of activity deliver all possible health benefits from exercise
  5. Applying a correction factor to Lee et al predicts a death toll from inactivity of 192,000 deaths per year – this is likely to still be a conservative estimate, and most likely puts inactivity as the leading cause of avoidable death in the UK by some considerable margin
  6. More research is needed in the field to fully quantify the likely death toll, the economic cost to the state and therefore how much needs to be invested in preventing inactivity through clever urban design and sports and physical activity interventions

 

 

 

 

 

 

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What’s the real UK death toll from inactivity? Part one – How?

What’s it got to do with movement?

This  post is the first in a two-part series aimed at looking at the true cost of inactivity in the UK in number of lives lost.  Why, this being a transport based blog?  Well, I believe that there is strong evidence that the built environment has a direct effect on peoples health.  We know that exercise is well correlated with lower mortality rates (e.g. meta-analysis (review of research done) here).  In fact, we see that the least fit 25% have mortality rates have four times that of the most fit 25%.  We see this pattern over and over again.  We also know that the number one cause of people not exercising is that people feel that they do not have time to exercise.  The answer, to me, seems to be that we need to help people fit more exercise into their day in time where they would otherwise be sedentary.  This could include more movement at work for some; but with people spending an average of 1 hour every day travelling, I argue that commute/travel time is the obvious candidate for fitting in more exercise.  Often, journeys could be moved at least partly to active travel modes with either a trivial increase in travel time, or often, a reduction in travel times once the quickest route has been worked out, some fitness has been gained and most appropriate equipment sourced.  There is strong evidence from Denmark that cycling to work reduces mortality (your chance of dying in any given year) by 28% once other factors (diet, economic group, other physical activity) are adjusted for  (from this study here).

How does exercise save lives?

Well, we know it prevents heart disease, reduces levels of certain types of cancer; this is a matter of scientific record.  But I think it goes further than that.  I would suggest that being fit, which leads on from exercising, has many other benefits when it comes to staying alive.  Sure, more cycling might increase your chance of being involved in an accident by some small measure over sitting in a train or driving for the same length journey, but it seems reasonable to suggest that your chances of surviving an accident as a fit person are significantly higher – you can control a fall better, and your better developed musculature, tendons and bone structure   will help reduce your chances of death in the event of an accident.  Suicide is the main cause of death amongst 5-34 year olds, and there’s some evidence that physical activity helps fight the depression that leads to it.

What if you still have a fall, a heart attack, or cancer?  Well, my opinion (as distinct from direct scientific research that I can access) is this.  The thing that finally kills you is you no longer being able to pump oxygenated blood round your body.  If you are fit you have more blood, bigger usable lung area, a bigger heart, and better developed blood vessels, then when the crisis comes you can stay alive for longer, giving your body a longer window to sort out the problem, or the magic of modern medicine longer to save you.  Even things as small as doctors being able to take blood samples to find out more about what’s making you ill – because you have bigger veins from exercising more (established long enough that it’s hard to find the studies online, but e.g. here: http://www.ncbi.nlm.nih.gov/pubmed/12640286) – can be expected to be significant (is significant, according to doctors that I’ve spoken to).

Beyond the death toll..

There is also the reduction in quality of life that comes with being less fit: regular exercise cuts the risk of dementia in old age by nearly 2/3; reduces the effects of type 2 diabetes and the chances of being affected by it in the first place by over 50%; there even more immediate short term effects, with reduction in obesity, most obviously, but also brings benefits as wide as increases in intelligence (certainly in children).

The scale of the problem

This all sounds very serious what with all this talk of death, dementia, and diabetes; but I don’t see it that way – I see a massive opportunity to give many people longer, more productive lives with less ill health and disability.  In part two of this blog I will explain why I think that it is possible that as many as A THIRD of all deaths in the UK – nearly 200,000 deaths per year – may be premature deaths which exercise would prevent.  Many of these deaths could be prevented by clever urban design which gives people the opportunity to exercise on a daily basis.  This is higher than previous analysis that I’ve found, but I think I have a strong case that is worth considering.

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