| Summary: | Coronary heart disease (CHD) mortality rates have fallen since the 1960s in the UK. The prevalence of type 2 diabetes (T2DM), in contrast, has increased markedly in recent decades. Few attempts have been made to examine the reasons for these striking, divergent time trends. The CHD mortality and T2DM prevalence trends likely reflect in part contemporaneous trends in incidence of these conditions. The broad aim of this thesis is therefore to analyse recent trends in CHD and T2DM incidence in the UK, in relation to trends in aetiological exposures and treatment use, and in relation to each other. This epidemiological research involves statistical analysis of pre-collected data from different UK-based observational data sources, each used according to their strengths: the British Regional Heart Study cohort, The Health Improvement Network primary care database, and the Whitehall II cohort. The principal findings are that favourable time trends in major modifiable aetiological exposures (smoking, blood pressure and HDL and non-HDL cholesterol) may explain half of a 62% decline in major CHD incidence in men over 25 years. Findings for women are similar. Much of the blood pressure decline, and a third of the non-HDL cholesterol decline was associated with increased preventive medication use. Conversely, unfavourable rising adiposity levels limited the scale of the decline in major CHD incidence, and explain an estimated one quarter of a rise in T2DM incidence since the 1980s. Major CHD incidence declined faster among those with T2DM, than without, corresponding to an attenuation of excess risk of CHD associated with T2DM. By highlighting what can be achieved in terms of reducing CHD, while showing the adverse impact of rising obesity levels, the results provide evidence to help inform future efforts to reduce CHD further and curb the rise in T2DM, in the UK and in other locations.
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