TEENAGERS in Hong Kong are suffering higher incidences of asthma and allergies than in other Asian nations while their counterparts in China are the least affected, a study says. Diet might be associated with the rise in asthma in the fast-growing economies of Hong Kong, Japan and Singapore, it said. A significant increase in asthma and the use of medications to treat it had also been detected among students at the Chinese University of Hong Kong. Researchers speculate that higher consumption of fast-food could be a factor in the increasing prevalence of allergic diseases. The study found 12.4 per cent of 13 to 14-year-olds surveyed had asthma in Hong Kong compared with just 3.1 per cent in more-highly polluted Guangzhou. The range differed in China with the highest level of 5.1 per cent recorded in Beijing. The prevalence of asthma in Japan was 13.2 per cent, Malaysia 6.8 per cent, the Philippines 12.3 per cent and Singapore 9.7 per cent. Those in Hong Kong suffered the highest proportion of rhinitis - inflammation inside the nose similar to hay fever with itchiness, sneezing, nasal discharge and blocked passages - with 44.5 per cent. This compares with a range in China of 20.5 to 33.7 per cent, 40.7 per cent in Japan, 29.1 per cent in Malaysia, 27 per cent in the Philippines and 41.1 per cent in Singapore. The next phase of the study would examine the causes behind the rise in allergies such as home environments, said Dr Christopher Lai Kei-wai, senior lecturer in the Chinese University of Hong Kong's medicine department. The presence of dust mites, which are abundant in Hong Kong homes because of the atmosphere, would be studied because they had been found to affect 90 per cent of asthmatics. Dr Lai was puzzled by the higher levels of pollution in China but the lower incidence of allergic disease. As both areas were dominated by Chinese ethnic groups, the difference could be due to environmental factors. Pollution levels, which can act as a trigger, will be studied to help explain the differing levels of allergic disease. Diet would also be examined. Links had been detected between breast-feeding and greater protection against allergies later in life, he said. A diet high in fish oil might provide some protection and high levels of salt could aggravate the disease, said Dr Lai. 'Some investigators would point out that the major change in the last decade or so is the increase of Western fast food with high-salt content,' he said. More fresh fish had been eaten in developing nations. 'Maybe because of fast food we tend to eat less.' Other factors which had been linked to asthma were exposure to viral infection in infancy and mothers smoking. The study was also conducted in Japan, Malaysia, Singapore and the Philippines. The worst countries for asthma and allergy sufferers had been found to be Australia and New Zealand, said Dr Lai.