india

Updated: Jul 23, 2019 02:01 IST

South Asians, even those who move to other countries, are at a higher risk of diabetes than people of most other ethnicities, and according to a study published last week in Nature Scientific Reports, the reason for this is their relatively low lean mass.

The research further establishes that this low lean mass has been a constant in South Asians for almost 11,000 years.

Higher lean mass is associated with superior performance in some, but not all, sports.

Mesolithic hunter-gatherer ancestors of South Asians were much taller, but low lean mass has characterised South Asians for at least 11,000 years, putting them at higher risk of type-2 diabetes and other non-communicable diseases (NCDs) such as heart disease, according to the study which analysed 197 archaeological and recent South Asian adult skeletons.

Height decreased by 8.5cm in men and 7.7cm in women when South Asians transitioned from hunting and gathering to farming around 9,000 years ago, but their lean mass (organ and muscle mass) has remained unchanged over the past 11,000 years, the study said.

Since changes in lean mass are unlikely over the next four to five generations, making lifestyle interventions are crucial to containing NCDs, which account for 60% of all deaths in India.

The study suggests that while height is determined by nutritional factors, physique (bone breadth and lean mass) reflects ecological pressures. “The decrease in height probably took place very quickly (over hundreds of years rather than thousands). After the initial drop in height with the adoption of farming, it then continued to decrease very slowly between about 5,000 years ago and today,” lead author Dr Emma Pomeroy, lecturer in the Evolution of Health, Diet and Disease, Department of Archaeology, University of Cambridge, said in an email interview. “The ancient origins of low lean mass in South Asians would be most consistent with long-term adaptations to ecological pressures, rather than more recent dietary change or the impact of 19th-20th century famines exacerbated by British colonial policy,” said the study. Ecological pressures include adaptation to a predominantly hot, equatorial climate, which may have led to selection for lower body mass (which generates less heat and increases heat loss through a greater surface area to volume ratio) to reduce thermal load. “Low lean mass is present at birth in South Asian babies compared with European babies; even after South Asian families migrate to other parts of the world, such as the UK, after several generations in this new environment, their children still have low lean mass compared with children of European ancestry. This strongly suggests a major heritable component to South Asian low lean mass, but the contributions of genetic, epigenetic and environmental conditions are still unclear,” said Dr Pomeroy, referring to a study on type-2 diabetes in migrant South Asians published in The Lancet in 2015. People of South Asian ancestry are at a higher risk of diabetes even after risks like unhealthy diet, sedentary lifestyles and obesity are factored in. For example, South Asians in London have a two to three times greater type 2 diabetes compared with those of European ancestry, with onset typically five years earlier and at a lower body mass index (by 5 kg/m2). “The implications of the study are that low lean mass is a very ancient characteristic, so it is unlikely to change much in the coming generations. This means that other interventions, especially the promotion of healthy lifestyles, are particularly critical to manage the growing health and economic burden of chronic diseases,” said Dr Pomeroy.

Building muscle mass and high fitness levels have the potential for averting diabetes, and even heart disease. “This study clearly shows origins of diabetes in Indians thousands of years ago; key factors being poor muscles and progressively shorter stature from adverse environment and poor nutrition. South Asians need to build lean muscles mass from an early age, so sports should be an integral part of school curriculum, along with muscle-building exercises and enhanced protein intake,” said Dr Anoop Misra, chairman of Fortis Centre for Diabetes, Obesity and Cholesterol, who has researched the link between low lean muscle mass in South Asians and increased risk of diabetes.