Respiratory illness in British schoolchildren and atmospheric smoke and sulphur dioxide 1973-7. II: longitudinal findings.

A study was set up to investigate the effects of annual changes in the levels of atmospheric smoke and SO2 on changes in health from 1973 to 1977 in primary schoolchildren from 28 randomly selected areas of England and Scotland. Changes in health were measured by taking the change in number of respiratory conditions reported from one annual examination to the next. The number of areas with data on pollution in each period was 5,9,17, and 14 respectively and within these areas the response rate varied from 65% to 74%. Altogether 857, 1436, 2702, and 2036 children respectively who were of white ethnic origin, aged 6 to 11, and had complete data on sex, social class, and changes in health were studied in each period. In 1973-4 the levels of pollution were highest and showed the greatest decline. The greatest annual mean change in smoke was a decrease from 71.9 to 50.5 microgram/m3 and in SO2 a decrease from 94.2 to 47.6 microgram/m3. However, no relation was found between improvement in health and decreasing levels of pollution. In subsequent years, when the levels of pollution were lower and showed smaller changes, change in health was also unrelated to changes in pollution. Thus no evidence was found to suggest that the levels measured during the study were harmful to health.