Vitamin D lowers heart-attack risk Men with low levels of vitamin D are at significantly greater risk of suffering a heart attack - and quite likely a fatal one - say researchers from the Harvard School of Public Health. Their 10-year study of 1,350 men is the latest to identify possible key health benefits of vitamin D, which is produced when the skin is exposed to sunshine. The researchers say the vitamin may protect against heart attacks in a number of ways, including helping to lower blood pressure and reduce artery calcification, Reuters reports. Serotonin link to weight control Serotonin, a brain chemical linked to mood and appetite, may be a key factor in why some people get fat, say researchers from the University of California, San Francisco - based on studies of worms. Serotonin appears to determine whether the body burns excess calories or stores them as fat, regardless of how much food is eaten, Reuters reports. Grumpy? Blame it on your diet Meanwhile, Cambridge University researchers say serotonin may be a key factor in aggression and impulsiveness - possibly explaining why many people aren't at their best on an empty stomach. Changes in diet and stress affect serotonin levels, which in turn appear to affect decision making, AFP reports. 'Our results suggest serotonin plays a critical role in social decision making by keeping aggressive responses in check,' says researcher Molly Crockett. Call for eye exercise periods The mainland's highly competitive education system is damaging the eyesight of millions of students, says the education ministry, which wants schools to introduce twice-daily eye exercise periods. About 32 per cent of primary-school students suffer from impaired vision; but among university students, the rate is almost 83 per cent, Reuters reports, citing Xinhua. Excessive eye strain accounts for an estimated 45 per cent of the total problem, Xinhua reports experts as saying. Mainland road-death toll doubles The death toll on the mainland's roads has almost doubled during the past two decade, and is likely to worsen significantly, say Johns Hopkins University researchers. From 1985 to 2005, the death rate rose to 7.6 fatalities per 100,000 people from 3.9 per 100,000. This compares with a global average of about 19 - but with more mainlanders able to afford cars, the researchers fear the worst, AFP reports. Contaminated air is plane nonsense You're no more likely to catch a bug aboard a crowded aircraft than in a bus or restaurant, according to a report by the Australian Transport Safety Bureau. Concerns the air in planes is full of contaminants is based on the widely held belief that it's continually recycled, AFP reports. But the bureau says the risk is 'no greater, and perhaps less, than' in any other place a large number of people gather. Toilets awash with bacteria On the other hand, public toilets are about as badly infected with bacteria as most people suspect. A study by researchers from Sul Ross State University in Alpine, Texas, of toilets along interstate highways found a variety of bacteria such as staph and E coli on taps, door handles, flushers and hand-dryers, says WebMD.