Environmental Factors in Cardiovascular Disease Doctoral Thesis

Cardiovascular disease is the main cause of death in Sweden and other developed countries. The purpose of this thesis is to assess the role of certain environmental factors in the etiology of cardiovascular disease, expressed as hypertension and myocardial infarction, focusing on aircraft noise, environmental tobacco smoke, drinking water hardness, and ambient air pollution. The thesis is based on two epidemiological materials, i.e. an Environmental Health Survey (EH-survey) in Stockholm county during 1997 and the Stockholm Heart Epidemiology Program (SHEEP), which is a county-wide case-control study of myocardial infarction 1992-1994. Aircraft noise exposure was assessed for 266 residents in the vicinity of Arlanda airport and 2693 inhabitants in other parts or the county who answered the EH-survey. The SHEEP-study, comprising 2246 cases of myocardial infarction and 3206 population controls, was used to investigate the importance of exposure to environmental tobacco smoke, intake of drinking water magnesium and calcium, and exposure to source-specific residential air pollution. Exposure to energy-averaged aircraft noise above 55 dBA was associated with an adjusted odds ratio for hypertension of 1.59 (95% CI 1.00-2.53), and maximum aircraft noise above 72 dBA was associated with an adjusted odds ratio of 1.76 (95% CI 1.12-2.77). A dose-response relation between aircraft noise and hypertension prevalence was suggested. Exposure to environmental tobacco smoke at home and work was associated with an increased risk of nonfatal myocardial infarction among never-smokers, both with regard to intensity, duration, time since last exposure, and cumulative dose. For example, spousal exposure of 20 cigarettes per day or more was associated with an adjusted odds ratio of 1.58 (95% CI 0.97-2.56), and cumulative combined exposure at home and work was associated with an adjusted odds ratio of 1.55 (95% CI 1.02-2.34) in the top decile of exposure. An inter-quartile range increase in the daily intake of drinking water magnesium was associated with an adjusted odds ratio for myocardial infarction of 1.01 (95% CI 0.87-1.17). There was no indication of dose-response for any of the drinking water parameters. An increased risk of fatal myocardial infarction was suggested in relation to long-term air pollution exposure, but not for incidence or nonfatal myocardial infarction. A difference in the 30-year average exposure to traffic-generated NO2 of 30 μg/m3 was associated with an adjusted odds ratio for fatal myocardial infarction of 1.51 (95% CI 0.96-2.16) and 2.17 (95 CI 1.05-4.51) for out-of hospital death. In conclusion, the results suggest that exposure to aircraft noise may be associated with an increased prevalence of hypertension, indicate that exposure to environmental tobacco smoke increases the risk of nonfatal myocardial infarction, do not support the hypothesis that drinking water hardness would protect against myocardial infarction, and point to long-term air pollution exposure as a risk factor for fatal myocardial infarction.