Washington: Researchers have suggested that laughter may not be the best medicine after all and could even be harmful to some patients. Researchers from Birmingham and Oxford, in the UK, reviewed the reported benefits and harms of laughter. They used data published between 1946 and 2013. They concluded that laughter is a serious matter. They identified benefits from laughter; harms from laughter; and conditions causing pathological laughter. Some conditions benefit from `unintentional` (Duchenne) laughter. Laughter can increase pain thresholds although hospital clowns had no impact on distress in children undergoing minor surgery (even though they were in stitches). Laughter reduces arterial wall stiffness,which the researchers suggest may relieve tension. Clowns improved lung function in patients with COPD and `genuine laughter` for a whole day could burn 2000 calories and lower the blood sugar in diabetics. Laughter also enhanced fertility: 36 per cent of would-be mothers who were entertained by a clown after IVF and embryo transfer became pregnant compared with 20 per cent in the control group. The paper has been published in The British Medical Journal.