Abstract
Living South Asians have low lean tissue mass relative to height, which contributes to their elevated type 2 diabetes susceptibility, particularly when accompanied by obesity. While ongoing lifestyle transitions account for rising obesity, the origins of low lean mass remain unclear. We analysed proxies for lean mass and stature among South Asian skeletons spanning the last 11,000 years (n = 197) to investigate the origins of South Asian low lean mass. Compared with a worldwide sample (n = 2,003), South Asian skeletons indicate low lean mass. Stature-adjusted lean mass increased significantly over time in South Asia, but to a very minor extent (0.04 z-score units per 1,000 years, adjusted R2 = 0.01). In contrast stature decreased sharply when agriculture was adopted. Our results indicate that low lean mass has characterised South Asians since at least the early Holocene and may represent long-term climatic adaptation or neutral variation. This phenotype is therefore unlikely to change extensively in the short term, so other strategies to address increasing non-communicable disease rates must be pursued.
Highlights
Non-communicable diseases (NCDs) accounted for 60% of global deaths in 2012 and place a growing burden of morbidity and mortality on populations worldwide[1]
Contemporary South Asians are generally characterised by relatively short stature[16], which is associated with lower glucose tolerance independently of body mass[17] and may act as a marker of type 2 diabetes (T2D) susceptibility, including during pregnancy[2,18]
Relative to stature South Asian skeletons demonstrate low lean mass compared with other worldwide populations, since most individuals fall below the reduced major axis (RMA) regression line for the total dataset (Fig. 3)
Summary
Non-communicable diseases (NCDs) accounted for 60% of global deaths in 2012 and place a growing burden of morbidity and mortality on populations worldwide[1]. We investigate the origins of a key factor implicated in this elevated susceptibility: low lean mass When and why this phenotype originated is currently unknown, and understanding the origins of South Asian low lean mass may have important implications for how we address the growing burden of NCDs in this population. Severe famines affected South Asia in the 19th and first half of the 20th centuries, which were exacerbated by British colonial policy and were associated with high mortality from starvation[31] This might have selected for genes associated with low lean mass, or might have reduced lean mass through mechanisms of trans-generational plasticity[2]
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