Diabetes, an ancient trail

Diabetes has modern India vexed. New research suggests that the disease might in fact be an ancient scourge. A study of skeletal remains dating from 11,000 years ago shows that Indians, and the larger South Asian population, have consistently had low lean mass, making them susceptible to Type 2 diabetes.

About 8.7 per cent of Indians between 20 and 70 years are diabetic, according to a World Health Organization estimate, earning the country the sobriquet ‘diabetes capital of the world’. While existing theories suggest that low lean mass (organ and muscle mass) might be a fairly modern condition, the new international research published in Nature Scientific Reports indicates otherwise. The findings suggest that low lean mass was prevalent in the Mesolithic population, which lived during 10,000-6,000 BC, a period when humans were slowly transitioning from hunter-gatherers to agricultural settlements. “We were surprised that low lean mass appears to date back such a long time, and was perhaps even more pronounced in the Mesolithic individuals,” says Emma Pomeroy from the Archaeology Department in the University of Cambridge, who has co-authored the study with Veena Mushrif-Tripathy from Deccan College Post Graduate and Research Institute, Pune, and academics Jonathan Wells, Tim Cole and Jay Stock.

Pomeroy studies skeletons to decode how humans adapt to their environment and the state of their health, whether in the past or present. “Research had shown that South Asians have a higher susceptibility to conditions like Type 2 diabetes, so an obvious question was, ‘why so?’. Previous work also suggested low lean mass might be a factor in this susceptibility, and data has characterised the rising rates of Type 2 [adult onset] diabetes in South Asia as a modern ‘epidemic’, meaning it is extremely important to understand ‘why’, in order to tackle the problem,” Pomeroy says over e-mail. In 2013, she reached out to Mushrif-Tripathy, assistant professor of Archaeology, who specialises in skeletal remains excavated from archaeological sites in India.

Over five years, they studied 197 skeletal samples — 59 female and 138 male — from archaeological sites in India, Sri Lanka, Pakistan and Bangladesh. While the 35 samples available in the Deccan College lab were manually measured and studied, the team depended on data from publications where direct access was not possible.

“We measured the length of the bone and the articular surface or joints. If it is a broad or a heavy bone, we can expect a corresponding articular surface area to sustain the body,” says Mushrif-Tripathy. The researchers made multiple measurements of the samples and compared the data for different populations across the world. “The length and width of the bone were considerably smaller in the South Asian population,” Mushrif-Tripathy says.

The oldest samples belonged to the Mesolithic hunter-gatherers of the Gangetic basins of Sarai Nahar Rai, Mahadaha and Damdama — all in present-day Uttar Pradesh — from around 11,000 years ago. The team used data from publications for this group. It also studied, through secondary sources, the bone measurements of the urbanised populations of Harappa (an area that corresponds to parts of India and Pakistan today) and Mohenjodaro in present-day Pakistan. The samples at Deccan College were from around 5,000 years ago, from excavations at Inamgaon and Mevasa in western Maharashtra, Mushrif-Tripathy says.

Pomeroy points out that previous studies have shown that the Mesolithic South Asians were generally tall; however, they may have also been lightly built compared to hunter-gatherers from other parts of the world. “But Mesolithic hunter-gatherers had not been compared with more recent South Asians or worldwide agricultural populations. Our results show clearly that low lean mass is a consistent pattern across the last 11,000 years in South Asia, and the strength of this pattern right back into the Mesolithic [age] was unexpected,” says Pomeroy.

The study, published in July, has also registered the fall in the height of South Asians over these many years. Titled Ancient Origins of Low Mean Mass Among South Asians and Implications for Modern Type 2 Diabetes Susceptibility , it mentions that as the population progressed from Mesolithic hunter-gatherers, it also shrank in stature. “We might predict total average declines in stature from Mesolithic hunter-gatherers to later populations of 8.5 cm and 7.7 cm in males and females, respectively, and a decline of the same magnitude across the 5,000 years since agriculture was adopted,” the study says.

Low lean mass, on the other hand, points out Mushrif-Tripathy, would have been a genetic adaptation precipitated by the environment. “Low lean mass helps us to adapt to climatic changes in South Asia,” she adds. As the population shifted gears and gave up hunting-gathering for agriculture, lifestyles changed, as did food habits. “We became more sedentary, our diets changed from protein-based food to carbohydrates, and we also registered a drop in height,” says Mushrif-Tripathy. The drop in height which occurred with the advent of food production also adds to the susceptibility to Type 2 diabetes, the study notes.

The study also points to a similar history of low lean mass among East Africans and native Australians, as also South Asian immigrants. With this condition deeply intertwined with ancient South Asian DNA, susceptibility to diabetes cannot be easily outgrown. “The interventions to prevent chronic diseases like Type 2 diabetes, in particular promoting healthy diets and active lifestyles, will be especially important for South Asian populations and people of South Asian ancestry across the world,” Pomeroy notes.

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