South Asia, commonly known as the Indian sub-continent, is home to almost one-quarter of the world’s population and is comprised of many diverse ethnic, linguistic and religious groups. The region includes countries like India, Pakistan, Bangladesh, Nepal, Sri Lanka and Bhutan, and is known to have an increased predisposition for Type 2 diabetes. In addition to the rather large population living in South Asia, a significant number of immigrants from the region are living in affluent Western nations. For example, the 2011 UK census reported that around 9% (694,000) of the country’s total residents were of Indian origin (2011). As a consequence, one could expect that a disease such as Type 2 diabetes affecting the ethnic South Asian sub-population would have potential implications on global health.
Diabetes mellitus has become an important health concern in the South Asian region with an estimated increase in the prevalence of diabetes of over 151% between 2000 and 2030. In the same period, diabetes is projected to increase by 40% (Wild et al, 2004). Studies have consistently demonstrated that South Asians are at an increased risk of developing diabetes in comparison to other ethnic groups (Mather and Keen, 1985). In the UK, the risk of diabetes is five times higher for immigrants from Pakistan and Bangladesh and three times higher for Indian immigrants, with an associated increased risk of complications, morbidity and mortality compared with the native white Caucasian population (Karlsen and Nazroo, 2002). Furthermore, South Asian patients with diabetes were younger and less obese compared to the native white Caucasians (Karlsen and Nazroo, 2002). The progression of diabetes is also known to be more rapid among South Asians. Mukhopadhyay et al (2006) reported that the decline in glycemic control over time was much more rapid among South Asians when compared to Europeans. Hence, it is apparent that diabetes among South Asians represents a significant health concern with differential risk factors and a more aggressive progression than in other ethnic groups.
Although there have been comprehensive reviews on diabetes in the Asian region, among South Asian immigrants living in developed countries and from individual South Asian countries such as India (Mohan et al., 2007), to date, not many studies have explored the prevalence and trends of the diabetes epidemic for the South Asian region. This article aims to discuss the prevalence of pre-diabetes and diabetes among adults from individual countries in the South Asian region, mainly India, Sri Lanka and Bangladesh, and to explore the differential factors reported to be associated with the development of diabetes in these countries.
Prevalence of diabetes and pre-diabetes
There is notable research evaluating the prevalence of diabetes and pre-diabetes for these three countries. In India, many studies have explored the prevalence of diabetes with estimates varying considerably between different geographical areas and between urban and rural populations. The Prevalence Of Diabetes in India Study (PODIS) reported an age-standardized prevalence of 4.3%, 4.4% and 4.5% for all adults, males and females, respectively (Sadikot et al., 2004). However, more recent studies based on urban populations or rapidly developing regions have reported a higher prevalence of diabetes (10.1%) (Ajay et al, 2008). While other research from rural Indian populations have demonstrated an even higher prevalence (12.5%–13.2%) (Vijayakumar et al, 2009).
A nationally representative diabetes and pre-diabetes study in Sri Lanka showed that the age-standardized prevalence of diabetes in Sri Lankan adults was 10.3% [males 9.8%, females 10.9%, P>0.05] (Katulanda et al, 2008). While a population-based survey conducted in four of the nine Sri Lankan provinces reported a prevalence of 14.2% and 13.5% of diabetes among males and females, respectively (Wijewardene et al, 2005). In 2000, a regional survey in a Sri Lankan suburb (Maharagama) showed that 6.5% of all adults, 5.0% of males and 6.6% of females were affected by diabetes (Malavige et al, 2002).
For diabetes in Bangladesh, the Bangladesh Institute of Research and Rehabilitation for Diabetes, Endocrine, and Metabolic Disorders (BIRDEM) patient registry showed that the mean age at diagnosis for Type 2 Diabetes was significantly lower in 2005 than in 1995 and the prevalence of diabetes increases in this period of time (Khanam PA, Mahtab H, Ahmed AU, Sayeed MA, Khan AKA, 2008). Also, the prevalence in Bangladesh is comparable to the corresponding estimates from other South-Asian countries such as India. Although, in both countries, the prevalence is low in the rural areas (Bangladesh=5.1%, India=3.8%), it is considerably higher in the urban areas (Bangladesh=10.2%, India=11.8%) (Srinath Reddy, K., Shah, B., Varghese, C., Ramadoss, A., 2005). The Maldives STEP survey was conducted in the country’s main commercial center, male with no prevalence data available for the rural sector (Aboobakur et al., 2010). National or regional studies from other South Asian countries demonstrate a substantial difference in diabetes prevalence between urban and rural populations with the prevalence consistently being higher amongst urban populations.
Research evaluating secular trends in the prevalence of diabetes and pre-diabetes were available for the three countries. The prevalence of diabetes in an urban Indian population has significantly increased from 8.3% in 1989 to 18.6% in 2005, and during the same period a similar increase from 2.2% to 9.2% was observed in a rural Indian population (Ramachandran et al., 2008).
Similarly, a study in Sri Lanka demonstrated that the age-standardized prevalence of diabetes had significantly increased from 2.5% in 1990 to 8.5% in 2000) in a rural community, with only a slight increase in urban Sri Lanka from 5.3% to 6.5% during the same period (Illangasekera et al, 2004).
The diabetes prevalence in Bangladesh to some extent proves similar in terms of comparison between rural and urban areas. To be specific, although the prevalence is low in rural areas (5.1%), it is considerably higher in urban areas (10.2%). The trends for the prevalence of pre-diabetes are not as definitive, for example, the increased prevalence observed in urban India in the period 1989 (8.3%) to 2000 (16.7%) had declined to 7.4% by 2006. Prevalence data in rural populations of India and Sri Lanka also showed a decline in prevalence during a similar period.
The increased prevalence of diabetes in the South Asian region could be attributed to regional changes in disease patterns from communicable to non-communicable diseases. The reasons attributed to this shift in disease pattern include: increased life expectancy, rapid population growth, unplanned urbanization, low literacy and increased external debt with resultant cutbacks on national healthcare expenditure. Collectively, these and related issues have contributed to the emergence of non-communicable diseases such as diabetes as a substantial regional health problem. This so-called ‘epidemiological transition’ could also be linked to the rapid industrialization occurring in the region as evidenced by the high prevalence of diabetes among urban residents. It is important to note that this epidemiologic transition and the rate of increase in non-communicable diseases such as diabetes in developing countries is far greater than that previously observed in high income countries, and hence there is a need to find solutions in a much shorter time frame and with far fewer resources.
Family histories, age, gender, BMI, WHR and diastolic blood pressure are significant risk factors for diabetes among South Asians. In addition, several studies have also demonstrated an association between diabetes and income, physical inactivity, graduate education and office-based occupation. The recent epidemic of diabetes in the region could be primarily due to environmental factors such as diet and physical activity levels coupled with a genetic predisposition. The strong evidence for the association between diabetes and family history highlights a genetic contribution to the prevalent epidemic (Mohan et al, 2003). In addition, in this ethnically diverse population, increasing age and body weight have also been demonstrated as important contributory factors. This is evident by the association between diabetes and increasing BMI, waist-hip ratio and abdominal obesity (Ramachandran et al, 2001). This may be the cause of the high susceptibility for diabetes and other metabolic abnormalities among South Asians.
People in the South Asia have faced under-nutrition for many generations; they are born smaller however coupled with subsequent obesity increases risk for insulin resistance syndrome in later life. A recent review has reported several dietary factors associated with insulin resistance among South Asians, such as higher intakes of carbohydrate, saturated fatty acids, trans-fatty acids and n-6 PUFA, and lower intakes of n-3 PUFA and fiber, hence the Asian diet may be an important contributory factor for the high disease prevalence (Misra et al, 2009). During recent years urbanization has risen unprecedentedly in the South Asian region. There are unhealthy lifestyle changes that are known to be associated with urbanization such as the lack of physical activity, changes in dietary habits and stress, all of which increases the risk of diabetes, as evidenced by the association shown in many South Asian studies. Rural-to-urban migration was also found to be a major risk factor for diabetes and obesity among South Asians. Migrants changed their lifestyles considerably within a decade and physical activity status quickly reached urban levels acquiring a metabolic risk similar to that of urban dwellers. Furthermore, increased mechanization of the agriculture industry, automation of daily activities, popularization of television and increased computer usage in rural areas are leading to changes in lifestyle with resultant decrease in physical activity.
An intra-urban disparity in the prevalence of diabetes has also been reported in India (Mohan et al, 2001). In contrast to developed countries, socially deprived urban South Asians reported relatively lower prevalence of diabetes and general obesity compared to their affluent counterparts. This observation could be partly explained by the differential purchasing ability with the affluent having a higher ability to purchase food, increasing energy intake and obesity; while on the other hand, the less affluent people are more likely to engage in manual labour increasing their physical activity level. However, socially deprived diabetes patients demonstrate poor glycemic control, which is likely to be lack of access to proper health care facilities and relative lack of knowledge.
To conclude, diabetes is a global crisis that threatens the health and economy of all nations, particularly developing countries in South Asian region. It is evident that several modifiable and non-modifiable risk factors play an important role in the pathogenesis of diabetes among South Asians. This epidemic is primarily driven by rapid urbanization, nutrition transition, and increasingly sedentary lifestyles. The diabetes epidemic in Asia is characterized by onset at lower BMI levels and younger ages compared with Caucasian populations. Although the average BMI is still relatively low in Asian populations, abdominal or central obesity is highly prevalent, creating the widespread “metabolically obese” phenotype. Poor nutrition in utero and in early life, as well as over-nutrition in later life, are contributing factors to the current diabetes epidemic amongst Asian populations.
Accumulating evidence strongly demonstrates that the majority of diabetes cases can be prevented through diet and lifestyle modification. However, the adoption of a healthy diet and lifestyle requires not only individual behavioral changes, but also changes in our food and built/social environments. Public health strategies that target the obesogenic environment are critical. Translating clinical and epidemiologic findings into practice requires fundamental shifts in public policies and health systems. To curb the diabetes epidemic, primary prevention through the promotion of a healthy diet and lifestyle should be a global public policy priority.