ArticlesRelation between age and cardiovascular disease in men and women with diabetes compared with non-diabetic people: a population-based retrospective cohort study
Introduction
Diabetes is a common cause of morbidity and premature loss of life.1 People with diabetes are up to four times more likely to have cardiovascular disease (CVD) as people without diabetes; CVD accounts for a large proportion of the excess mortality related to diabetes.2, 3, 4 Evidence suggests that even in the absence of pre-existing vascular disease, middle-aged people with type 2 diabetes have a similar risk of coronary heart disease (CHD) to those without diabetes who have had a myocardial infarction.5 The idea of diabetes as a coronary equivalent led to widespread changes in the approach to reduction of CVD risk in this population.6, 7, 8 In the past 5 years, increasing evidence has emerged that lends support to the use of cardioprotective agents in patients with diabetes, including lipid-lowering therapy, aspirin, and angiotensin-converting-enzyme inhibitors, and the adoption of all of these strategies simultaneously.9, 10, 11, 12
An issue that concerns many practitioners is the age at which vascular-protection strategies should be started in people with diabetes. Although randomised controlled trials on this topic have rarely included participants under the age of 40 years, many clinical practice guidelines recommend application of existing evidence when treating these individuals. National cholesterol guidelines in several countries recommend use of the same therapeutic targets for people with type 2 diabetes as those recommended for secondary prevention of coronary-artery disease.6, 7, 8 In this respect, all adults with type 2 diabetes, irrespective of their age, are regarded as being at high risk of fatal or non-fatal coronary events. In 2005, the International Diabetes Federation published global guidelines suggesting that people with type 2 diabetes should be judged as being at high risk of CVD if older than 40 years, even in the absence of pre-existing CVD or coronary risk factors.13 The American Diabetes Association takes a similar approach; however, their recommendations do not distinguish between people with type 1 or type 2 diabetes.14 By contrast, the UK National Institute for Health and Clinical Excellence uses risk-assessment tables to select individuals with type 2 diabetes for primary-prevention strategies.15 In the absence of an appropriate prediction tool for type 1 diabetes, these guidelines use an age threshold of 35 years for recommendation of primary prevention with statins in people with type 1 diabetes without pre-existing vascular disease or other high-risk features.16
The relation between age and risk of CVD in people with diabetes has not been fully elucidated. Predictive algorithms created from diabetic cohorts have shown that age is a strong predictor of CHD, but little is known about the absolute risk of these events in younger people with diabetes.17 Moreover, the appropriateness of existing age thresholds for identification of people with diabetes who are at high risk of CVD is not known. Therefore, we used a population-based approach to investigate the age at which individuals with and without diabetes develop a high risk of CVD. We postulated that the absolute rate of cardiovascular events in adults younger than 40 years with diabetes would be less than the rate conventionally characterised as high risk. We explored this issue using two commonly used definitions of high risk: a fatal or non-fatal CHD-event rate equivalent to a 10-year risk of 20% or more; and a rate of CHD equivalent to that of previous myocardial infarction. Our secondary aims were to ascertain: the ageing equivalent of diabetes-associated cardiovascular risk; and the effect of diabetes on sex-related differences in CHD.
Section snippets
Patients
We used the Registered Persons Database to identify all residents of Ontario aged 20 years and older who were eligible for coverage under the Ontario Health Insurance Plan on April 1, 1994. As in other Canadian provinces, hospital, laboratory, and physicians' services are funded through a single-payer system administered through the Ontario Government; therefore these data sources include records for almost all residents in the province.
We used the Ontario Diabetes Database to identify
Results
The study population consisted of 379 003 people with diabetes and 9 018 082 without this disease. People with diabetes were older than those without the disease (60·8 vs 42·6 years, p<0·0001); a substantially lower proportion of them were younger than 40 years (9·6% vs 51·3%), and a higher proportion were 65 years or older (44·7% vs 12·6%). 573 515 individuals in our cohort had one or more outcome events during the 6-year follow-up period, 18·3% (n=104 702) of whom had diabetes.
In both
Discussion
Our findings highlight the higher CVD risk in people with diabetes than in those without diabetes, both in relative and absolute terms. We showed that both for men and women, diabetes confers an equivalent degree of risk as ageing about 15 years. Age also seems to be an important predictor of CVD in people with diabetes, with younger people being at lower risk than older people. Even with use of the broadest definition for CVD, our data suggest that the CVD risk in people with diabetes does not
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