Effect of ambient levels of smoke and sulphur dioxide on the health of a national sample of 23 year old subjects in 1981.

BACKGROUND There is concern that, despite the fall in air pollution levels since the 1950s, there may still be adverse effects at current levels. A study was carried out to investigate the association between air pollution and respiratory symptoms in 23 year old subjects in 1981. METHODS Data on cough, phlegm, and wheeze were available on 11,552 members of the 1958 national birth cohort. Counties in the UK were ranked by annual average level of black smoke and sulphur dioxide (SO2), and then divided into five groups. The subject's county of residence determined their categorisation of pollution exposure. The association between air pollution exposure and respiratory symptoms was examined by logistic regression, adjusting for social class, sex, and smoking. RESULTS The ranges of the air pollution groups were 2.0-13.0, 13.1-18.7, 19.6-20.8, 21.0-25.8, and 26.1-55.1 micrograms/m3 for black smoke, and 7.0-36.4, 36.7-42.7, 43.0-50.5, 52.0-59.3, and 60.9-87.7 micrograms/m3 for SO2. The overall prevalences of cough, phlegm, wheezing since age 16, and wheezing in the past year were 13.3%, 10.3%, 9.4%, and 4.4%, respectively. Phlegm symptoms increased with increasing smoke levels with evidence of a plateau. Cough and wheeze were not associated with black smoke; no symptom was associated with SO2. In the subgroup with wheeze at ages 16-23 there was no effect of smoke level on phlegm. CONCLUSIONS Low ambient levels of black smoke were associated with decreased prevalence of phlegm symptoms in young adults in the UK in 1981. The effect was evident below the current EC guideline of 34-51 micrograms/m3 annual black smoke. In 1991 the annual mean smoke level for each county ranged from 3.4 to 26.5 micrograms/m3, spanning all but the last exposure group used here. This is consistent with the existence of adverse and possibly chronic effects at current levels.