Diabetes epidemiology: present and future

It is 1959 ± today's diabetic clinic is over and the physician sits, alone, pondering his afternoon's work. He has seen 25 patients, each of whom was carefully weighed and had a urine test for glucose performed before coming to his consulting room. They were a mixture of juvenile-onset and maturity-onset patients, some treated with (bovine) insulin, others with the recently introduced oral hypoglycaemic agents. A few had home urine testing results to discuss but for most the discussion revolved around symptoms of polyuria, thirst or hypoglycaemia. Finally complaints of numb or painful feet, angina or deteriorating vision were sought but, in the absence of any proven therapeutic interventions, little or no speci®c action could be taken. A further appointment for 6 months was then made. It was hard for the honest physician to feel that he was doing more than impotently following the natural history of the disease. Forty years have transformed the activities of the diabetic clinic. The physician works in a team, sharing her responsibilities with nurses, dietitians, podiatrists and others. New insulins, new oral agents, new delivery devices and new monitoring equipment abound and the increased understandings and management techniques for the long-term complications of diabetes have transformed the whole ethos of complications review from depressing passivity to optimistic activity. It is 1999 ± today's epidemiologist studying diabetes is rather like the physician of 40 years ago, laboriously recording and analysing the mortality of people with diabetes and able to see little cause to be positive or optimistic. Like his counterpart in 1959 he lacks the tools, in this case data, to undertake the analyses he would wish to perform to gain the full picture of the disease he is studying. The situation is illustrated well by the two papers in this edition of Diabetic Medicine from the British Diabetic Association Cohort Study of people with insulin-treated diabetes [1,2]. The impressively large cohort was recruited from a variety of disparate sources which vary substantially in size, composition and, one suspects, comprehensiveness of coverage. A large amount of effort over several years was then necessary to `clean up' the demographic data on the subjects from each source and check for double-counting before attempting to ̄ag the records of each subject with the appropriate national population register. Thereafter all prevalent and incident deaths have been recorded and analysed using death certi®cate information and it is the results of these analyses which are presented here. The information obtained is both interesting and useful. The excess mortality in people with diabetes is con®rmed, this being present at all ages; the absolute excess mortality is greater in males though the relative risk is generally greater in females. The standardized mortality ratio peaks in early adult life and then reduces as background mortality rates increase, though the absolute risk of death attributable to diabetes rises progressively in each decade of life. Causes of death are fairly unsurprising, with acute metabolic derangements having the greatest impact in the early years (and having a larger impact on males than females in middle life) and the vascular effects of diabetes dominating after age 30 years. It is particularly noteworthy that at all ages cardiovascular deaths exceeded deaths from renal disease and that in the age range 20±39 years over 85% of cardiovascular deaths could be attributed to the presence of diabetes. Lessons for clinical practice (or at least further research) are clear: can we impinge further on acute metabolic problems, should we be beginning cardiovascular risk factor management in the teenage years to reduce mortality in the third and fourth decades, should this management be further strengthened in later years where the greatest absolute mortality lies? By combining the data with those from intervention studies, sensible health economic assessments of the impact of interventions in different age groups can begin to be made. In addition, those peripheral to clinical practice but with a legitimate interest in the mortality pro®le of people with diabetes, such as the insurance industry, now have up-to-date data. The information is, however, depressingly limited in its extent. The studies give us no information on comorbidities, on other in ̄uences on mortality in the subjects studied, on the nature and extent (and therefore utility) of diabetes-related and other therapeutic interventions, on morbidity and disability rather than death and on changes over time. We have real cause to believe that changes in clinical practice in the last 10 years are likely to be making signi®cant differences to both morbidity and mortality, yet we have no ready way to monitor and chart improvement, let alone detect failure. The diabeto-epidemiologist of the future should not have to rely on raw mortality statistics from ad hoc patient cohorts to assess the impact of diabetes on health. The challenge of the information technology age is to link existing and new data-sets across populations to give a full picture of the effects of both illness and interventions and we in diabetes care are ideally placed to take the lead. With a population diabetes register linked to prescribing data, other disease registers, hospital morbidity statistics and mortality data, we could be one of the ®rst clinical groups to be able continuously to monitor both the safety and effectiveness of a broad range of activities in real time and in a real world population. Our practice could become truly evidence based, with the evidence coming not from the arti®cial world of the `gold standard' randomized controlled clinical trial but from the real world of real people with diabetes. L