Diseases and Different Ethnic Groups - Asians

Cardiovascular related illnesses are still the highest cause of death in the United Kingdom. In men coronary heart disease tops the list of causes of death closely followed by cerebrovascular disease.

The pathophysiology of cardiovascular disease, i.e. atherosclerosis is still only barely understood. However, the risk factor profile is well established (although more soft risk factors are still under research e.g. homocysteine levels). The important risk factors that we need to be aware of and to look for are:

• Smoking
• Diabetes mellitus
• Hypertension
• Hyperlipidaemia
• Family history
• Past history of ischaemic heart disease
• Obesity and lack of exercise.

Compounded on this is that the United Kingdom consists of a very versatile population and it has become apparent that cardiovascular disease is more prevalent in certain subgroups - especially men from the Indian subcontinent. We have also become aware that some of the major clinical trials may not be easily correlated to patients from ethnic groups as patient cohorts have usually involved caucasian subjects.

Research to try and tease out the differences in cardiovascular disease in ethnic minorities and the causes for these differences have been underway for a few years. Unfortunately, most of this research has been performed in the United States and there are no cohort studies in the UK that include enough ethnic minority patients at present.¹

In 1999 the UK health survey was performed in which members of the population were randomly sent questionnaires regarding their health. Various aspects of health were reviewed.

Presence of angina in various ethnic groups

Presence of stroke in various ethnic groups

There have been various theories as to the observed difference of cardiovascular disease in ethnic minorities. Possibilities include genetic variation and dietary influence. It is suggested that the risk factor profile is different in terms of intensity and prevalence. Lets explore some of these risk factors.

Diabetes mellitus

The 1999 Uk health survey reported that prevalence of diabetes is greater in men than women. The observed prevalence was markedly higher in Bangladeshis (10.6%) - although Pakistanis and Indians were not far off (8.7% and 7.7% respectively).² For the Bangladeshi and Pakistani population this represents an almost 5 times higher prevalence than the general population. The prevalence in black caribbean men was similar to Indians. However, black caribbean women had the highest prevalence of diabetes mellitus amongst all women.

Hypertension

In the Health Survey for England (2001) the prevalence of hypertension was reported as over 25% in those over 40 years of age and nearly 50% in those aged 80 or over.⁷ Hypertension is more frequently encountered in ethnic minorities. The average blood pressure is different in the differing ethnic groups. Another difference is the development and presence of target organ damage, for example, afro-caribbean patients have an increased prevalence of left ventricularar hypertrophy (a predictor of mortality and morbidity independent of other risk factors).⁷

Hyperlipidaemia

There is no clear evidence that a difference in lipid levels exists between ethnic minorities.³ Despite this plasma lipid concentrations are greater in patients of South Asian descent (i.e. from the Indian subcontinent and East Africa - note that the BHF define South AsianS as only from Indian countries).⁴ This may explain the differences in prevalence of cardiovascular disease seen between them and the black caribbean population.

Black caribbean populations appear to have higher HDL fractions and lower triglycerides. It is postulated that these changes probably represent genetic variations e.g. polymorphism of hepatic lipase genes.⁸

Obesity

In the 1999 UK health survey obesity and raised waist-hip ratio was higher in those with cardiovascular disease and more so in Indian and Bangladeshi women.²

Other theories

• The pattern of atherosclerosis is thought to be different in african american and caucasian patients - but this remains inconclusive. Levels of C-reactive protein (CRP) , an inflammatory marker, appear to be higher in ethnic groups and has been independently associated with cardiovascular disease - although the part it plays in the pathophysiology of atherosclerosis is still poorly understood.³ Another theory is that genetic differences resulting in changes in the bioavailability of nitric oxide, a potent vasodilator may be involved.⁹
• The most likely cause for the observed disparity in cardiovascular disease between ethnic groups probably relates to greater risk factor clustering - leading to a metabolic syndrome characterised by dyslipidaemia, obesity and hypertension.^3,10 This is supported by studies that have shown higher fasting insulin levels in asian indians in the united states when compared to caucasians of a similar age and body mass index. This supports the presence of impaired insulin metabolism and use.
• The BHF states that the increased rate of cardiovascular disease in South Asians is due to four essential factors: excess exposure to risk factors, greater susceptibility (e.g. environmental such as urban lifestyle), presence of a certain risk factor not yet determined and due to the fact there are fewer competing causes of death in this group e.g. cancer.⁴
• However, it has been argued that the observed differences actually relate to the fact that ethnic minorities are under investigated and under treated.^3,11

The Framingham study has provided us with valuable insights in to the risk factors for cardiovascular disease and the time course of disease. This provided the Framingham risk function to determine the cardiovascular risk in a patient based on their risk factors. However, the cohort of patients has been mainly caucasian making it difficult to correlate to ethnic minority groups,¹² JBS guidelines suggests multiplying calculated risk by 1.5.⁵

Recently a risk calculator for determining the 10 year risk of coronary heart disease and cardiovascular disease for ethnic minorities has been developed and is based on the Framingham study.^1,13

• In the first instance this should be the same as your management of all patients.
• However, when considering the risk of a patient from a cardiovascular view point we need to take in to account their ethnicity - this includes cultural differences.
• BHF recommend that practices keep a register with ethnic codes and diseases
• All patients should have their blood pressure, weight and height checked - these are easy to perform and non-invasive.
• Patients with a strong family history of diabetes, hypertension and hyperlipidaemia should have these parameters regularly checked e.g. annually.
• Have a high index of suspicion for the presence of multiple risk factors and use the risk calculator to determine the patients risk.
• Lifestyle modifications must be reinforced when ever possible and even if risk is low e.g. weight reduction, salt reduction, healthy low-fat diet and increased exercise.
• The above measures may require dedicated services available in the patients language e.g. gujarati smoking cessation service.
• Hypertension, diabetes mellitus and hyperlipidaemia should be aggressively treated and patients should be educated e.g. community ethnic diabetes mellitus meetings with professionals and patients.