High Risk of Diabetes & Heart Disease in South Asians

Introduction

South Asians, including individuals from India, Pakistan, Bangladesh, Sri Lanka, and Nepal, face disproportionately high rates of Type 2 diabetes (T2D) and cardiovascular disease (CVD). Despite advancements in healthcare, this ethnic group continues to experience a greater burden of these chronic conditions compared to other populations. The Mediators of Atherosclerosis in South Asians Living in America (MASALA) Study and other research initiatives offer valuable insights into this issue, revealing the biological and lifestyle factors that contribute to these elevated risks.

Understanding these risk factors is essential for healthcare providers, researchers, and public health policymakers to develop targeted strategies for prevention and management. This article explores the prevalence of T2D and CVD among South Asians in Australia, investigates the underlying mechanisms contributing to these risks, and discusses potential interventions to mitigate the burden of these diseases in this population.

Prevalence of Type 2 Diabetes and Cardiovascular Disease in South Asians

South Asians exhibit a significantly higher prevalence of T2D and CVD compared to other ethnic groups. According to the MASALA Study, nearly half of this population is at risk of developing T2D and CVD at younger ages. Research indicates that the prevalence of T2D in South Asians is 1.5 to 4 times higher than in European populations. This elevated risk is observed even among individuals with a normal or slightly elevated body mass index (BMI), which complicates early diagnosis and intervention efforts typically based on BMI thresholds.

In Australia, the diabetes prevalence among South Asians is notably high. Studies reveal that South Asians are approximately 3 to 4 times more likely to develop T2D compared to the general Australian population. According to the Australian Diabetes Society, the prevalence of diabetes among South Asians is estimated at around 15-20%, compared to about 8-10% in the overall Australian population. Furthermore, South Asians often develop T2D at a younger age, with research indicating an onset that can be 5 to 10 years earlier than in other ethnic groups. Pre-diabetes rates are also high, with an estimated 20-30% of South Asians in Australia at risk of progressing to T2D.

In addition to T2D, South Asians in Australia experience higher rates of cardiovascular disease. The prevalence of coronary artery disease among South Asians is about 2 to 3 times higher than in the general Australian population. Research published in The Medical Journal of Australia highlights that South Asians have a significantly higher incidence of heart disease, with some studies showing up to 30-50% higher rates compared to other ethnic groups. Hypertension is also prevalent, affecting around 30-40% of South Asians in Australia. The risk of stroke is elevated as well, with South Asians experiencing stroke rates about 50% higher than the general Australian population.

Impaired Beta Cell Function in the Pancreas

A central hypothesis for the heightened risk of T2D among South Asians is impaired beta cell function in the pancreas. Beta cells are responsible for producing insulin, a hormone crucial for regulating blood sugar levels. In South Asians, beta cells may be inherently less efficient, leading to early onset insulin resistance and subsequent T2D. This inefficiency could stem from genetic predispositions or environmental factors that disrupt the beta cells’ ability to respond adequately to rising blood glucose levels.

Studies have demonstrated that South Asians have lower insulin secretion capacity compared to other populations. This reduced capacity is often present even before diabetes onset, suggesting a genetic component that predisposes South Asians to impaired beta cell function. Chronic low-grade inflammation, often associated with obesity and visceral fat accumulation, may further impair beta cell function, exacerbating the risk of T2D.

The concept of “beta cell exhaustion” is particularly relevant for South Asians. Over time, individuals with insulin resistance require beta cells to produce more insulin to maintain normal blood glucose levels. This increased demand can lead to beta cell burnout, where the cells can no longer produce sufficient insulin, resulting in T2D.

Low Muscle Mass

Low muscle mass is another contributing factor to the heightened risk of T2D and CVD in South Asians. Muscle tissue plays a crucial role in glucose metabolism, serving as a primary site for glucose uptake and utilization. Lower muscle mass reduces the body’s capacity to manage glucose effectively, increasing the risk of insulin resistance and T2D. This issue is exacerbated by sedentary lifestyles and dietary habits high in refined carbohydrates and low in protein, further increasing risk.

Low muscle mass is not only a factor in diabetes but also in CVD. Muscle mass influences overall metabolic health, and reduced muscle mass is associated with higher levels of inflammatory markers and a greater risk of metabolic syndrome. South Asians, particularly women, tend to have lower muscle mass compared to other ethnic groups, which may partly explain the higher prevalence of these conditions.

Research suggests that South Asians may have different muscle fibre compositions, with a higher proportion of type I muscle fibres, which are less effective at handling glucose than type II fibres. This difference in muscle fibre composition could contribute to the higher risk of insulin resistance and metabolic disorders in this population.

Ectopic Fat Deposition in Organs and Muscle

Ectopic fat deposition, or the accumulation of fat in non-adipose tissues such as the liver, pancreas, and muscles, is a critical factor contributing to the elevated risk of T2D and CVD in South Asians. This fat is metabolically active and harmful, leading to chronic inflammation and insulin resistance. South Asians are prone to visceral fat accumulation, which contributes to metabolic syndrome—a cluster of conditions increasing the risk of heart disease, stroke, and T2D.

Visceral fat, stored within the abdominal cavity surrounding vital organs, is particularly detrimental to cardiovascular health. It produces inflammatory markers and hormones that contribute to atherosclerosis, characterized by plaque build-up in arterial walls. This process narrows the arteries, increasing blood pressure and the risk of heart attacks and strokes.

South Asians often exhibit a unique fat distribution pattern, characterized by a higher percentage of body fat, particularly in the abdominal region, despite having a normal BMI. This “thin-fat” phenotype is associated with a higher risk of insulin resistance, T2D, and CVD. Ectopic fat in the liver, known as hepatic steatosis, is concerning as it can lead to non-alcoholic fatty liver disease (NAFLD), further increasing the risk of T2D and CVD. This is demonstrated clearly in the Yudkin-Yajnik Paradox. Dr Yudkin, an European with a BMI of 22.3 had a body fat percentage of 9.1, while his South Asian friend, Dr Yajnik, who also had the exact same BMI was shown to have a body fat percentage of 21.2%!

The Role of Genetics

Genetic factors significantly contribute to the heightened risk of T2D and CVD among South Asians. Several genetic variants associated with insulin resistance, beta cell dysfunction, and fat distribution have been identified. For instance, the TCF7L2 gene, which influences insulin secretion and glucose metabolism, is more prevalent in South Asians and strongly associated with increased T2D risk.

Additionally, South Asians have a higher prevalence of the “thrifty gene” hypothesis, suggesting that certain genetic traits advantageous during periods of famine are now detrimental in environments with abundant food. These genes may predispose South Asians to store more fat, particularly visceral fat, and exhibit exaggerated insulin responses to carbohydrate intake, increasing T2D and CVD risk.

While genetics play a role, they do not fully account for the increased risk. Environmental factors, lifestyle choices, and diet significantly influence the expression of these genetic traits and the development of chronic diseases.

Evolutionary Adaptation Hypothesis

An intriguing hypothesis posits that vulnerabilities to T2D and CVD in South Asians may be rooted in evolutionary adaptations. The “thrifty gene hypothesis” suggests that certain genetic traits, beneficial in ancestral environments characterized by periodic food scarcity, have become detrimental in modern contexts of constant food availability. These adaptations would have favoured efficient fat storage and energy utilization during times of abundance, ensuring survival during famines.

In today’s world, with high-calorie foods readily accessible and lower physical activity levels, these once-beneficial traits may predispose South Asians to excessive fat accumulation, particularly visceral and ectopic fat, and heightened insulin responses to carbohydrate intake. This evolutionary mismatch may explain why South Asians are more susceptible to insulin resistance, beta cell dysfunction, and the subsequent development of T2D and CVD at lower BMI levels than other populations.

This perspective underscores the importance of understanding the historical and environmental context of genetic predispositions. While genetics alone cannot fully explain the high prevalence of these diseases, they provide a crucial piece of the puzzle, highlighting the need for personalized prevention and treatment approaches that consider both genetic and environmental factors.

The Role of Diet and Lifestyle

Dietary habits and lifestyle choices are critical in influencing the risk of T2D and CVD in South Asians. Traditional South Asian diets, rich in carbohydrates such as white rice and sugar-laden foods, contribute to rapid blood glucose level increases. Coupled with low physical activity levels, these dietary patterns accelerate insulin resistance and cardiovascular complications.

The transition from traditional diets to more Westernized eating patterns, including processed and high-calorie foods, has worsened this scenario. The rising consumption of unhealthy fats, such as trans fats, and sugar-sweetened beverages among South Asians contributes to obesity, insulin resistance, and other metabolic disorders.

Physical inactivity is another major concern. Sedentary lifestyles are increasingly common among South Asians, particularly women and older adults. Lack of regular physical activity contributes to weight gain, low muscle mass, and poor cardiovascular health, increasing the risk of T2D and CVD.

Stress and mental health also play a role. Chronic stress, prevalent in South Asian communities due to socio-economic factors, can lead to increased cortisol levels, promoting visceral fat accumulation and insulin resistance. Mental health issues, often stigmatized and underreported, can further exacerbate the risk of T2D and CVD by influencing dietary choices and physical activity levels.

Potential Solutions and Interventions

Given the high risk of T2D and CVD in South Asians, a multifaceted approach to prevention and management is essential. Several strategies can help mitigate these risks:

1. Culturally Tailored Dietary Interventions: Developing dietary guidelines that respect traditional South Asian foods while promoting healthier choices is crucial. Emphasizing low glycaemic index foods, increasing fibre intake, and incorporating adequate proteins can help manage blood glucose levels and improve cardiovascular health.
2. Physical Activity Promotion: Encouraging regular physical activity, tailored to individual preferences and cultural practices, can improve insulin sensitivity and cardiovascular fitness. Programs that incorporate traditional activities, such as dance or group exercises, can be effective in engaging the South Asian community.
3. Education and Awareness: Increasing awareness about the risks of T2D and CVD among South Asians is vital. Community-based education programs that address cultural beliefs and provide practical advice on lifestyle changes can empower individuals to make healthier choices.
4. Healthcare Provider Training: Training healthcare providers to understand the unique risk factors and challenges faced by South Asians can improve early diagnosis and management. Providers should be equipped to offer culturally sensitive care and support tailored to the specific needs of this population.
5. Policy Changes: Public health policies that address the social determinants of health, such as access to healthy foods and opportunities for physical activity, can support efforts to reduce the prevalence of T2D and CVD among South Asians.
6. Genetic Research and Personalized Medicine: Continued research into genetic factors and their interactions with lifestyle and environmental factors can lead to more personalized prevention and treatment strategies. Understanding genetic predispositions can help identify individuals at higher risk and implement targeted interventions.

Conclusion

The high risk of Type 2 diabetes and cardiovascular disease among South Asians in Australia is a complex issue with multifaceted causes, including impaired beta cell function, low muscle mass, ectopic fat deposition, and genetic predispositions. Addressing these challenges requires a comprehensive approach that incorporates dietary changes, increased physical activity, cultural sensitivity, and targeted healthcare strategies.

By understanding the unique factors contributing to the elevated risk of these chronic diseases, healthcare providers, researchers, and policymakers can work together to develop effective interventions and support the South Asian community in achieving better health outcomes. Acknowledging and addressing the specific needs of this population is crucial for reducing the burden of Type 2 diabetes and cardiovascular disease and improving overall well-being.

References

1. MASALA Study:
   • Kanaya, A. M., et al. (2014). “Understanding the high prevalence of diabetes and cardiovascular disease in South Asians living in the US: The MASALA study.” Diabetes & Vascular Disease Research. 
2. Impaired Beta Cell Function:
   • Anjana, R. M., et al. (2014). “Impaired insulin secretion and increased insulin resistance characterize high-risk Indian offspring of parents with type 2 diabetes.” Diabetes Care. 
3. Low Muscle Mass:
   • Misra, A., & Khurana, L. (2009). “The metabolic syndrome in South Asians: Epidemiology, determinants, and prevention.” Metabolic Syndrome and Related Disorders. 
4. Ectopic Fat Deposition:
   • Petersen, K. F., et al. (2007). “The role of skeletal muscle insulin resistance in the pathogenesis of the metabolic syndrome.” Proceedings of the National Academy of Sciences. 
5. Genetics and the Thrifty Gene Hypothesis:
   • Neel, J. V. (1962). “Diabetes mellitus: A ‘thrifty’ genotype rendered detrimental by ‘progress’?” American Journal of Human Genetics. 
6. Diet and Lifestyle Factors:
   • Patel, S. A., et al. (2017). “Association between dietary patterns and risk of type 2 diabetes in South Asian populations: Findings from the CARRS study.” Public Health Nutrition.