More than 2,000 years ago, Hindu physicians noting cases of “honey urine” commented that such cases “passed from generation to generation in the seed” and also were influenced by “injudicious diet.” Physicians today have rediscovered those deadly insights, which we now rephrase by saying that diabetes involves both genetic and environmental factors, and possibly also intro-uterine factors affecting the fetus during pregnancy. Evidence for a role of genes includes the 10-times-higher risk of getting diabetes if you have a diabetic first-degree relative (a parent or a sibling) than if you don’t. But diabetes, like hypertension, is not one of those simple genetic diseases in which mutation in the same gene is responsible for the disease in every patient. Instead, dozens and dozens of different genetic susceptibility factors for diabetes have been identified, many of them united only by their common feature that a mutation in any of those genes may result in high blood-glucose levels due to insulin resistance.

As of the year 2010, the number of diabetics in the world was estimated at around 300 million. This value may be underestimate, because there were likely to be other undiagnosed cases, especially in medically under-surveyed countries of the developing world. The growth rate in the number of diabetics is about 2.2% per year, or nearly twice the growth rate of the world’ adult population: i.e., the percentage of population that is diabetic is increasing. If nothing else changes in the world except that the world’s population continues to grow, to age, and move to cities (associated with a more sedentary lifestyle and hence increased prevalence of diabetes), then the number of cases predicted for the year 2030 is around 500 million, which would make diabetes one of the world’s commonest diseases and biggest public health problems. But the prognosis is even worse than that, because other risk factors for diabetes (especially affluence and rural obesity) are also increasing, so that the number of cases in 2030 will probably be even higher. The current explosion in diabetes’ prevalence is occurring especially in the Third World, where the epidemic is still in its early stages in India and China, the world’s two most populous countries. Formerly, considered a disease mainly of rich Europeans and North Americans, diabetes passed two milestones by the year 2010: more than half of the world’s diabetics are now Asians, and the two countries with largest number of diabetics are now India and China. ~ Page 432

India provides excellent examples of those subnational differences. (For this information I am grateful to Professor V. Mohan, of the Madras Diabetes Research Foundation.) the average prevalence in India as of the year 2010 was 8%. But there was little diabetes in India until just a few decades ago. Surveys in 1938 and 1959, in large cities (Calcutta and Mumbai) that are today strongholds of diabetes, yielded prevalence of only 1% or less. Only in 1980s did those numbers start to rise, first slowly and now explosively, to the point where India today harbors more diabetics (over 40,000,000) than any other nation. The reasons are essentially the same as those behind the diabetes epidemic around the world: urbanization, rise in standard of living, the spread of calorie-rich sweet and fatty fast foods cheaply available in cities to rich and poor people alike, and increased sedentariness associated with replacement of manual labor by service jobs and with video games and television and computers that keep children (and adults) seated lethargically watching screens for hours every day. …… Page 437