Basically nothing is as bad for you as smoking. Short of fairly obvious things like blunt-force trauma or falling out of buildings, anyway. That is a fact worth keeping in mind when you read newspaper headlines about health.
On the front page of the Telegraph's print edition on Friday ran the headline: 'Lazy lifestyle can be as deadly as smoking'. The Mail runs the same story, saying: 'A lack of exercise is as dangerous as smoking.'
Now, remember: Nothing that you do in your daily life, even if you are a lumberjack or an oil-rig diver or whatever, is as deadly as smoking. I pretty much promise you that. Serving with the British Army in Afghanistan is, on one admittedly superficial reading of the statistics, not as dangerous as smoking. (As far as I can work out, rather more than 10,000 UK men and women have served in Afghanistan; fewer than 500 have died; odds of death less than 1 in 20. Smoking-related diseases kill somewhere between one-half and two-thirds of lifelong smokers.)
So why do we see so many headlines saying 'X is as deadly as smoking'? In recent years I've seen 'Is a handshake as deadly as smoking?' (no, it's not); 'sitting can be more dangerous than smoking' (no, it can't); and 'high-protein diets are as dangerous as smoking' (no, they're not).
Smoking was, as I've written before, a bit of a one-off, from an epidemiological point of view: there's almost nothing else which lots of us do all the time, and lots of us don't do at all, and which is straightforwardly poisonous. The effects of every other lifestyle factor are much harder to tease out. But it is possible, to an extent. Public Health England (PHE), the excellent and wise body behind the 'lack of exercise' study, has done that for inactivity, and they think that about 85,000 deaths a year, around one-sixth of the total, are related to sedentary lifestyles.
By curious coincidence, that's roughly how many people die of smoking-related illnesses each year (actually smoking kills a few more, around 100,000, but close enough). So! Lack of exercise is as deadly as smoking, right? Case closed!
Except that less than one person in five in Britain smokes and, as PHE points out, rather more than that fail to take exercise. That is, in fact, the whole point of their report: they say that almost two-thirds of Britons are not taking the recommended minimum amount of exercise. Out of 64 million Britons, therefore, about 13 million smoke, but more than 40 million don't run around enough - and yet still smoking kills more than lack of exercise does.
If we take those numbers completely baldly, smoking is more than three times as deadly as a sedentary lifestyle. Of course it's more complicated than that, because 'not enough exercise' is a tricky thing to define and measure, but that will be in the right ballpark.
You can see where the confusion arises: lack of exercise, or eating too much meat, or whatever, kills as many people as smoking (roughly), ergo it's as dangerous as smoking. But it's simple innumeracy; it's like saying that, say, crossing the road is as deadly as Ebola - in fact much deadlier, since about 270,000 pedestrians are killed each year on the roads, compared to a piddling 5,000 or so deaths from Ebola. But of course if you cross the road once, you aren't very likely to die, whereas if you get Ebola, you are. One is much, much deadlier than the other, and, paradoxically, it's not the one that kills the most people.
Anyway. There you have it: being lazy is very bad for you, but it is absolutely nowhere near as bad for you as smoking. Because nothing is. Just remember, every time you see the headline 'Is X as bad for you as smoking?', unless X is 'being shot', the answer is almost certainly no.