| Nauru, 2002 | 41 |
| Nauru, 2010 | 31 |
| Papua New Guinea, traditional | ~0 |
| Papua New Guinea, urban Wanigela | 37 |
| Aboriginal Australians | |
| traditional | ~0 |
| Westernized | 25–35 |
| Native Americans | |
| Chile Mapuche | 1 |
| U.S. Pima | 50 |
The numbers in the right-hand column are prevalences of diabetes in percent: i.e., the percent of the population suffering from Type-2 diabetes. These values are so-called age-standardized prevalences, which have the following meaning. Because Type-2 prevalence in a given population increases with age, it would be misleading to compare raw values of prevalence between two populations that differ in their age distributions: the raw values would be expected to differ merely as a result of the different age distributions (prevalence would be higher in the older population), even if prevalences at a given age were identical between the two populations. Hence one measures the prevalence in a population as a function of age, then calculates what the prevalence would be for that whole population if it had a certain standardized age distribution.
Note the higher prevalences in wealthy, Westernized, or urban populations than in poor, traditional, or rural populations of the same people. Note also that those lifestyle differences give rise to contrasting low-prevalence and high-prevalence (over 12%) populations in every human group examined except Western Europeans, among whom there is no high-prevalence population by world standards, for reasons to be discussed. The table also illustrates the rise and subsequent fall of prevalence on Nauru Island, caused by rapid Westernization and then by the operation of natural selection against victims of diabetes.
Buried within that national average prevalence of 8% is a wide range of outcomes for different groups of Indians. At the low extreme, prevalence is only 0.7% for non-obese, physically active, rural Indians. It reaches 11% for obese, sedentary, urban Indians and peaks at 20% in the Ernakulam district of southwest India’s Kerala state, one of the most urbanized states. An even higher value is the world’s second-highest national prevalence of diabetes, 24%, on the Indian Ocean island of Mauritius, where a predominantly Indian immigrant community has been approaching Western living standards faster than any population within India itself.
Among the lifestyle factors predictive of diabetes in India, some are also familiar as predictors in the West, while other factors turn Western expectations upside down. Just as in the West, diabetes in India is associated with obesity, high blood pressure, and sedentariness. But European and American diabetologists will be astonished to learn that diabetes’ prevalence is higher among affluent, educated, urban Indians than among poor, uneducated, rural people: exactly the opposite of trends in the West, although similar to trends noted in other developing countries including China, Bangladesh, and Malaysia. For instance, Indian diabetes patients are more likely to have received graduate and higher education, and are less likely to be illiterate, than non-diabetics. In 2004 the prevalence of diabetes averaged 16% in urban India and only 3% in rural India; that’s the reverse of Western trends. The likely explanation for these paradoxes invokes two respects in which the Western lifestyle has spread further through the population and been practised for more years in the West than in India. First, Western societies are much wealthier than Indian society, so poor rural people are much better able to afford fast foods inclining their consumers towards diabetes in the West than in India. Second, educated Westerners with access to fast foods and sedentary jobs have by now often heard that fast foods are unhealthy and that one should exercise, whereas that advice has not yet made wide inroads among educated Indians. Nearly 25% of Indian city-dwellers (the subpopulation most at risk) haven’t even heard of diabetes.
In India as in the West, diabetes is due ultimately to chronically high blood glucose levels, and some of the clinical consequences are similar. But in other respects—whether because lifestyle factors or people’s genes differ between India and the West—diabetes in India differs from the disease as we know it in the West. While Westerners think of Type-2 diabetes as an adult-onset disease appearing especially over the age of 50, Indian diabetics exhibit symptoms at an age one or two decades younger than do Europeans, and that age of onset in India (as in many other populations as well) has been shifting towards ever-younger people even within the last decade. Already among Indians in their late teens, “adult-onset” (Type-2 or non-insulin-dependent) diabetes manifests itself more often than does “juvenile-onset” (Type-1 or insulin-dependent) diabetes. While obesity is a risk factor for diabetes both in India and in the West, diabetes appears at a lower threshold value of obesity in India and in other Asian countries. Symptoms also differ between Indian and Western diabetes patients: Indians are less likely to develop blindness and kidney disease, but are much more likely to suffer coronary artery disease at a relatively young age.
Although poor Indians are currently at lower risk than are affluent Indians, the rapid spread of fast food exposes even urban slum-dwellers in India’s capital city of New Delhi to the risk of diabetes. Dr. S. Sandeep, Mr. A. Ganesan, and Professor Mohan of the Madras Diabetes Research Foundation summarized the current situation as follows: “This suggests that diabetes [in India] is no longer a disease of the affluent or a rich man’s disease. It is becoming a problem even among the middle income and poorer sections of the society. Studies have shown that poor diabetic subjects are more prone to complications as they have less access to quality healthcare.”
Benefits of genes for diabetes
The evidence for a strong genetic component to diabetes poses an evolutionary puzzle. Why is such a
