Lessons Learned From Epidemiology of Type 2 Diabetes in South Asians: Kelly West Award Lecture 2024

Abstract

South Asia has high prevalence rates of type 2 diabetes (T2D). Until the 1990s, the prevalence of T2D within South Asia was low but much higher in the South Asian diaspora living abroad. Today, high prevalence rates of T2D are reported among those living in South Asia. T2D in South Asians presents with unique clinical features described as the "South Asian phenotype" that include younger age at onset of diabetes than in White Europeans, much lower BMI, hyperinsulinemia and greater insulin resistance, rapid decline in β-cell function resulting in low insulin reserve, low muscle mass, and greater ectopic fat deposition, especially in the liver. Also, prevalence of impaired fasting glucose is higher among South Asians than prevalence of impaired glucose tolerance. Genetic predisposition combined with intrauterine fetal programming (low vitamin B12 intake and high folate intake) increases susceptibility to T2D, from birth. In later life, overnutrition, especially a high carbohydrate intake with refined grains of higher glycemic index, coupled with low physical activity likely triggers the T2D epidemic in South Asians. Additionally, there are emerging risk factors like air pollution. Preventing T2D in South Asians requires a multifactorial approach, including improvements in maternal and fetal nutrition with special reference to vitamin B12 and folate intake, decreasing refined carbohydrate and increasing protein and fiber intake in the diet, increasing physical activity, and control of air pollution. Lessons learned from epidemiology of T2D in South Asians could be useful to other developing countries that are in earlier stages of epidemiological transition.

Graphical abstract

Figure 1

Comparison of diabetes prevalence among migrant Indians in the U.S. and urban Indians in India (data are from Gujral et al. [22]).

Figure 2

A: Age-wise prevalence of diabetes in ICMR-INDIAB study. *P for trend <0.001. B: Age at diagnosis of South Asians, White Europeans, and Black Europeans of Afro-Caribbean and African descent. Adapted from Wright et al. (26).

Figure 3

A: Prevalence of diabetes stratified by BMI in the ICMR-INDIAB study. B: Prevalence of T2D in South Asians and White Europeans stratified by BMI in a U.K. population-based study. Left panel, women; right panel, men. Adapted from Sattar and Gill (27).

Figure 4

“South Asian phenotype” (28–36). NAFLD, nonalcoholic fatty liver disease; Vit, vitamin.

Figure 5

Genetic risk of β-cell dysfunction in South Asians (partitioned polygenic scores [pPS]) (87).

Figure 6

Lessons learned from epidemiology of T2D in South Asians.