Stupid health advice - like nagging people to eat less salt when you've good evidence it won't make a blind bit of difference - isn't a bad thing just because it's a patronising, expensive waste. It also gets in the way of the stuff that actually works. Smoking is a good example.

The best evidence we have about smoking comes from the Oxford study that first showed it killed people: the 50-year follow up was published last year. Smokers die 10 years younger than non-smokers. But quitting helps. If you stop at 30 your life expectancy is the same as if you had never smoked. If you quit at 50 you more than halve the extra risk you have built up.

Deaths from smoking in Britain outnumber deaths from all cancers combined. You're probably getting my drift: smoking is catastrophically bad but it's never too late to give up. As a hospital doctor, if I tell one one of my patients this I will probably make them miserable, guilty or plain irritated. That's not my job. I see enough daily misery without adding to it.

But between 1972 and 2003 there were 39 different trials that looked at the effects of doctors telling more than 31,000 people to quit smoking. They showed that being hounded to quit smoking by their doctor made people almost twice as likely to pack it in. No one imagines that smoking is good for them, and having that fact shoved in their face by their doctor led to an extra 2.5% of tobacco addicts managing to quit - an absolute difference that sounds small, but means a lot.

Around 12 million Britons smoke. Advising them all to quit should lead to almost 300,000 extra of them actually managing it. Given that every second smoker will die of their habit, that would save a very large number of lives.

There's so much rubbish health advice floating about that we have to ignore most of it just to get on with our lives. But while most of it is useless, some of it is life-saving. And the people who glibly spout meaningless trash are responsible for distracting us from that.