Diabetes epidemic in the South Asian Diaspora: action before desperation

The tsunami wave of diabetes mellitus and its health and economic consequences is threatening much of the world. The need to prevent and control this debilitating chronic disease is urgent, before desperation sets in.

The International Diabetes Federation estimated that the number of people living with diabetes will rise from 194 million in 1993 to 333 million in 2025.¹ In the USA, the prevalence of type 2 diabetes has doubled from 4% to 8% over the past four decades. In Asia, the epicentre of the coming pandemic of diabetes, profound socioeconomic and demographic changes, with increasing affluence and changing lifestyles causing obesity, are fuelling the problem. Consequently, the Indian subcontinent could be one of the leading contributors to global diabetes by 2025.

The South Asian diaspora is prone to developing diabetes, a phenomenon known since the mid 20th century. South Asians develop diabetes earlier in life, at lower levels of obesity, suffer longer with complications and have a subsequent higher mortality risk than their White European counterparts. Childhood obesity and consequent type 2 diabetes is also no longer rare.

UK South Asian subgroups, in all their heterogeneity, have an increased prevalence of diabetes: population data using the oral glucose tolerance test in adult populations gives an estimate of about 20%.² UK South Asians have a four- to six-fold increased prevalence of type 2 diabetes compared to the White European population. Unsurprisingly, cardiovascular disease³ is very common. Standardized mortality rates for South Asians are 50% higher than the general population, with a great deal of premature mortality. Complications other than ischaemic heart disease include renal failure and stroke.

So why are South Asians at an increased risk of diabetes? No specific genetic hypothesis has yet explained the excess of diabetes in South Asians. In the 1960s, Neel postulated the ‘thrifty genotype’ hypothesis⁴ whereby people who possessed genes facilitating fat storage during food abundance would have a survival advantage during later famine. The current state of affairs—abundance with little famine—would make such an advantage a liability. There is little evidence, however, that over recorded history the Indian subcontinent has been particularly prone to famines compared to other parts of the world (with the possible exception of the short period when the British ruled India). The environment clearly plays an aetiological role. An urban/rural divide has been described in several countries and in particular in India. Urbanization, rather than migration per se, as a fuel to the development of diabetes is unquestionable. The UK South Asian population is certainly more sedentary than its counterpart White European population.

Impaired glucose tolerance is a precursor to diabetes and a propensity to diabetes may develop early in life.⁵ Low birth weight and intrauterine growth retardation in South Asians have been postulated to carry increased risks of diabetes later in life.⁵ South Asians born in the UK to mothers themselves born in the UK also have comparatively low birth weight. Yajnik showed that babies of Indian mothers had higher cord blood insulin concentrations than White European babies and these higher levels correlated with sub-scapular skinfold thicknesses. These ‘thin-fat’ Indian babies become more insulin resistant than their White European counterparts.⁶ The phenomenon of low birth weight with subsequent accelerated growth is widely seen in South Asian children and may contribute to the development of insulin resistance.

Increased visceral adiposity (measured as waist circumference) is more common in South Asians and denotes an individual at higher cardiovascular risk. The prevalence of obesity in India is low (2.2%) but diabetes prevalence in some metropolitan areas is as high as 12%.⁷ South Asians suffer the consequences of being overweight at lower levels than their White European counterparts, leading the World Health Organization to propose lower cut-off points for obesity for Asian ethnic groups. Fat distribution possibly also differs in South Asians, with a new hypothesis suggesting they have an insufficiently developed lower limb fat compartment and more developed metabolically active compartments (upper body). This might explain South Asians' tendency to possess atherogenic dyslipidaemia and a predisposition to endothelial dysfunction.

How do we translate this understanding of basic science into clinical practice? There is a paucity of clinical trial data to help. Screening, early diagnosis and aggressive control of hyperglycaemia and other cardiovascular risk factors may reduce morbidity and mortality from diabetes. Lifestyle interventions to prevent hyperglycaemia and diabetes would be even better. Trials of lifestyle interventions for the prevention of diabetes are starting in UK South Asians. Several studies have shown that lifestyle changes and some medications may prevent type 2 diabetes. Whilst we await specific trial data for South Asians, it is likely that similar strategies targeting weight reduction would be more cost effective than treating the consequences of diabetes. Lifestyle improvements at all ages, together with effective management of other cardiovascular risk factors, are sensible and should be instituted without delay in high risk groups.

What, however, defines a high risk individual? Are Framingham cardiovascular risk tables accurate enough to apply to pre-diabetic South Asians? The South Asian Health Foundation advocates weighting of risk calculations.⁸ The National Institute for Clinical Excellence (NICE) in England and Wales recommends that all patients with diabetes with a 10 year CHD risk >15% be offered a statin. This accommodates ∼70% of all patients with diabetes and the remaining 30% simply fail to meet this threshold due to age alone. Denying cardiovascular prevention interventions to these individuals whilst atherosclerosis and subclincial disease develop is questionable, particularly in South Asians, who develop diabetes much earlier and have greatly accelerated atherosclerosis. Type 2 diabetes is widely accepted as a cardiovascular risk equivalent⁹ and the evidence base for treatment of people at high cardiovascular risk with statins (HMG CoA reductase inhibitors) is so compelling that all South Asians with diabetes should be considered for such therapies.

The cost of inaction is clear and should fuel the development of integrated public health approaches. Investment in such strategies will not only improve the lives of millions across the globe but also produce healthier economies. It is therefore timely that the South Asian Health Foundation has convened an international meeting to focus on diabetes in the South Asian Diaspora.¹⁰ Appropriate action now is better than desperation in the decades to come.