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...migration and increased life expectancy have also been major contributors (Lipscombe and Hux, 2007). The UK has a large South Asian population comprising migrants from Bangladesh, India and Pakistan. The prevalence of diabetes among South Asian adults in the UK is estimated to be approximately 20% compared with 3-4% in Caucasians (Barnett et al, 2006). The purpose of this review is to examine the literature on diabetes and CVD in South Asians and to discuss novel options for improving health care in this high-risk population.
Key words
- South Asians
- Cardiovascular disease
- Novel healthcare strategies
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The prevalence of diabetes and cardiovascular disease in this population is disproportionately high: diabetes is almost six times greater (Mather and Keen, 1985) and mortality from CVD nearly twice as common compared with the local Caucasian population (Chaturvedi and Fuller, 1996). Epidemiological studies have shown that this excess risk is due to a higher prevalence of insulin resistance and an unfavourable CV risk profile more commonly seen in South Asians (McKeigue et al, 1991). This is further compounded by economic deprivation, poor access to healthcare, and cultural practices that make it difficult to deliver optimal care. This is thought to be due to a combination of genetic and environmental factors (Reddy and Yusuf, 1998).
The genetics of type 2 diabetes is complex and involves interaction of several genes with the environment (Barroso, 2005; Ramachandran et al, 1992). Although no single gene has been implicated in the causation of type 2 diabetes, better understanding of the pathogenesis and improved techniques of genetic testing have allowed identification of several susceptibility genes associated with the condition (Grant et al, 2006; Ramachandran et al, 2006). Most of these studies have been in Caucasians and until recently there have been very few genetic studies in South Asians. Despite the widely-held belief that South Asians may be genetically different to other ethnic populations, studies involving South Asians have so far not demonstrated any significant differences between the ethnic groups. On the other hand, features of insulin resistance have been identified in early childhood in South Asians suggesting a possible genetic predisposition (Krishnaveni et al, 2005).
In contrast, evidence for environmental influence is much stronger. Studies comparing prevalence of diabetes between migrants and native South Asians have shown a much higher prevalence in migrants (Dhawan et al, 1994; Bhatnagar et al, 1995). Studies from India (Ramachandran et al, 1992; Ramachandran et al, 1997) have shown significantly greater prevalence in those residing in urban compared with rural areas. These studies support the assertion that environmental influences play an important role in the pathogenesis of type 2 diabetes. In addition to the increased prevalence, diabetes occurs at least a decade earlier in South Asians with substantially greater rates of microvascular complications such as nephropathy and retinopathy even at diagnosis (Burden et al, 1992). The burden of long-term complications, therefore, is much higher in this ethnic group.
The higher rates of CVD in South Asians parallel the high prevalence of diabetes. In the UK, for example, mortality from cardiovascular causes is 40-50% greater among South Asians compared with the local Caucasian population (Chaturvedi and Fuller, 1996). The difference in risk is further exaggerated in individuals with diabetes with mortality rates as much as three times that seen in Caucasians. This pattern persists even in second generation migrants. In one study comparing South Asians with six other racial groups, mortality from CHD was highest among South Asians (Palaniappan et al, 2004). Another study found a much higher prevalence of sub-clinical atherosclerosis (Anand et al, 2000). The precise reasons for this excess cardiovascular risk are not fully understood, but it is widely believed that the increased prevalence of diabetes and adverse metabolic risk factors commonly seen in this ethnic group are (at least in part) responsible. In fact, the relationship between CHD and diabetes is so strong that there may be a common pathogenic mechanism linking the two (Lebovitz, 2006).
The relationship between diabetes and CHD can be further explored through studies of the metabolic syndrome. Originally described by Reaven (1988), this syndrome comprises the co-existence of insulin resistance, hypertension, raised triglycerides and...
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