When History Meets Health: Understanding Diabetes in South Asian Communities

Have you ever wondered why British South Asians are six times more likely to develop Type 2 diabetes, even at a lower weight, compared to the White British population?

Type 2 diabetes (T2DM) is a chronic condition characterised by two main mechanisms:

1.      Insufficient insulin production: reduced insulin production from the beta islet cells in the pancreas leads to reduced uptake of glucose (sugar) from the blood.

2.      Intrinsic insulin resistance: a cellular-level defect where the body's tissues, particularly muscle and fat, don't respond to insulin as well as they should, requiring more insulin to achieve the same effect on blood sugar

Development of high sugar levels can damage blood vessels and lead to several complications such as diabetic nephropathy (kidney damage), diabetic retinopathy (eye complications), and peripheral neuropathy (damage to nerves in the extremities). There is currently no cure for Type 2 diabetes; however, it can be prevented and managed through lifestyle interventions and/or medication.

Several studies on UK South Asian populations, especially Indians, indicated a higher incidence of pre-diabetes and T2DM compared to other ethnic groups. UK south Asians are also more likely to develop T2DM at younger age, BMI (Body Mass Index), and experience associated complications such as those mentioned above. Waist circumference, a clinical measure of central obesity, is an important risk indicator of T2DM. People from South Asian backgrounds are more likely to store visceral fat, due to decreased insulin production and sensitivity. Studies have shown that these populations have a higher risk at lower waist circumference measurements (80cm for women, and 90cm for men) compared to men from other ethnic groups (94cm).

A historical explanation:

Many complex factors contribute to avoidable differences in health. Until recently, only diet and lifestyle choices have been held accountable for the diabetic rise in the South Asian region. However, new studies have shown this vulnerability may trace back to the 89 years of British colonial rule over the Indian subcontinent, known as the British Raj, during which the region experienced 25 major famines. It is theorised that due to inequalities of food distribution and crop availability, epigenetic adaptations arose to store enough energy as fat, leading to increased fat storage and elevating their risk of diabetes, obesity, and heart conditions.

These genes pass on generation after generation, posing as a possible explanation for the decreased insulin production by the beta islet cells in the pancreas. It is possible that exposure to a singular famine can have multi-generational effects of metabolic dysfunction, let alone 24 major famines during a certain time frame. In today's world, this starvation adaptation has become a disadvantage where food is readily available and can be known as an ‘evolutionary mismatch’. This can also explain the lower waist circumference threshold as a risk of diabetes.

The epigenetic adaptations

During a case-control study over an 8-year period, it was found that South Asians who developed T2DM had a higher level of DNA methylation, an established indicator of epigenetic changes. DNA methylation is a process by which DNA is modified to alter gene expression, turning genes ‘off’ or silencing them. In T2DM, these methylation patterns can affect genes involved in glucose metabolism, and insulin secretion as well as other diabetic related processes. The relationship between T2DM and DNA methylation is strong, making it a potential biomarker for future screening of pre-diabetes and early intervention.

Unlike permanent genetic mutations, epigenetic adaptations caused by historical famine tend to be very stable in the first generation. If future generations are not exposed to the same stress, these epigenetic adaptations gradually lessen over time. It is still unknown what the exact timeline for full epigenetic reversal is in humans, but the evidence from famine studies does suggest the possibility to diminish across generations.

What does this mean for South Asians?

Whilst historical context may explain today's incidence rates, it does not mean these risks are unavoidable. Diet and exercise are modifiable factors to almost any disease risk. If diet, training and recovery are optimised, there is no strong evidence that these epigenetic traits predispose South Asians to building less muscle- a powerful and proven strategy in improving diabetes and metabolic health.

Targeting diet and physical activity

South Asians tend to have a higher BMI (Body Mass Index) compared to Caucasians. This can be explained by the diverse, but carbohydrate rich diet, including rice and flatbread. Several dietary imbalances include a low intake of fibre, monosaturated and polyunsaturated fatty acids (‘healthy fats’). These lead to associated insulin resistance and dyslipidemia. Involving these into the diet can significantly reduce the incidence of diabetes.

As briefly mentioned above, physical activity is known to be an effective tool in preventing the onset of T2DM. However, with migration and urbanisation, South Asians are participating 50-75% less in physical activity compared to European ethnic groups. The UK NICE guidelines recommend that South Asians undergo at least 150 minutes of aerobic resistance training. A study from the University of Glasgow suggests an addition of 20 minutes a day for South Asians to receive similar benefits as their European counterparts.

Ultimately, it is vital for healthcare providers to know who they are prescribing to. This means taking time to explore patient backgrounds, and the historical factors that may shape their health risks today. When this understanding is combined with high-quality clinical evidence, they can offer more patient-centered care that empowers patient needs, especially those who have faced unfair historical predispositions to poor health outcomes.

By Salma Eldali