Gel halts spread of HIV US researchers have developed a vaginal gel, using a compound found in breast milk, that appears to prevent the sexual transmission of the human immune-deficiency virus (HIV) in monkeys. 'The results are very encouraging,' says Ashley Haase from the University of Minnesota. The anti-HIV ingredient is glycerol monolaurate, which is found in breast milk and already used in cosmetics and medicines. It is also being considered for use in tampons because of its antibacterial properties, WebMD reports. The researchers say they need to do many more studies before conducting human trials. Depression triggers heart attack Women suffering severe depression may be at greater risk of fatal heart attack, say US researchers, based on analysis of data from 63,000 women between 1992 and 2004. Depression is common after heart attack or stroke, but the Columbia University study suggests it may be a trigger. Although sudden cardiac death appears to be particularly linked with antidepressant use, researchers say this may mean those using drugs were more depressed, AP reports. Fitness boosts longevity The health benefits for men over 50 of taking up regular exercise are as significant as those from giving up smoking, say Swedish researchers, based on a study of 2,200 men over 30 years. The exercise regime has to be followed for five to 10 years before the full benefits are apparent, but from then on the men had the same life expectancies as those who had always exercised. The Uppsala University study notes about one in every two middle-aged western men doesn't exercise regularly, AFP reports. Look on the bright side More bad news for pessimists: optimists live longer and tend to be healthier. The conclusion by University of Pittsburgh researchers is based on analysis of the Women's Health Initiative study of more than 100,000 women aged 50 and over since 1994. Optimists are 30 per cent less likely to die from heart disease. They're also less likely to smoke or have high blood pressure or diabetes, Reuters reports. Team leader Hilary Tindle says the study doesn't prove that negative attitudes cause ill health, but there seems to be a link. Financial crisis hits fairies The global economic slowdown appears to be putting the bite on the tooth fairy: children are earning about 10 per cent less for their teeth this year than they did last year, according to a US dental insurance company that has been monitoring payouts for more than a decade. Average payments are down from US$2.09 per tooth to US$1.88, WebMD reports.