Next time someone calls you an old grump and tells you to get a life, take them seriously. It's not likely your heckler knows it, but they're reflecting a vast amount of medical research. People who are bored, miserable, grumpy, stuck in dull occupations, frustrated with their circumstances and - worst of all - lack a sense of humour, are heading for trouble. Lives eked out in quiet desperation are shortened by misery. All the facets of grumpiness - irritation because your job's boring; that seething you do in the supermarket queue or at the lift door; the rage you feel when someone cuts in front of you in traffic - can tip you into the high-risk heart disease category. Believe it or not, most of these things have been studied and found to add up to a picture of stress that doesn't get released in a healthy way. As your teeth clench, your knuckles whiten and your growling deepens, your blood vessels tighten and your heart starts pumping, ready for action. But the action your body's conditioned to expect is something pretty big, such as staving off a sabre-toothed tiger. So, when that car cuts in front of you or your boss demands another pointless report, your angry mind sends the sort of signals that your danger-alert system - the sympathetic nervous system - interprets as a tiger closing in fast. This shoots out adrenalin to help you run for it. Unfortunately, when you're standing at a lift door that's been slammed in your face by a supersonic 'door-close' presser, there's nowhere to run, nowhere to hide. There's just teeth to grind and arteries to squeeze. If you happen to be a smoker, those arteries get even more squeezed and your body less oxygen. No way will you escape any predators in that condition. But what can people do? Face down the sabre-toothed tiger? The best thing is to laugh in his face. Among my favourite areas of research are population and personality studies showing that optimists live longer than pessimists and that people with a good sense of humour have a better chance of staving off heart disease. A good laugh not only keeps your heart happy, it also helps you burn calories. A team from the Vanderbilt University in Nashville, Tennessee, lured volunteers into metabolic measuring units cunningly disguised as cheap motel rooms and told them they were studying their emotional responses to videotapes. They were then told to lie back on reclining chairs, but not to move and not to talk - just watch the television screen. As they watched, their oxygen consumption, carbon-dioxide production and heart rates were measured to see how many calories were burned. For the first half hour, they were shown pictures of boring English landscapes. Then there were comedy clips, followed by pictures of sheep in more of that boring English landscape. When the researchers tallied their results, they found that the comedy had their volunteers burning 20 per cent more calories than the English sheep scenes. The team calculated that 10-15 minutes of laughter could burn up 50 calories and a daily 'laughter workout' could burn off a couple of kilograms in a year. It seems a slow way to go about losing weight, but it's fun. So, the next time your boss, your colleague, your neighbour or your spouse becomes irritating, find a way to find them funny. It'll do your body - and soul - a lot of good.