RAPID industrialisation in developing countries has produced advancements on the social and economic front, resulting in economic prosperity and better living standards. On the flip side, it has also led to an increase in lifestyle-related diseases.
According to the report of the International Diabetes Federation on the estimated projections regarding diabetes and impaired glucose tolerance (IGT) in South-East Asians, the South-East Asian countries have the highest prevalence of diabetes in the world. Since India comprises 85 per cent of the adult population of South-East Asia, the major contribution to diabetic population in South-East Asia is from India.
India has nearly 33 million diabetics today. What is worrisome is that the gap between the scenario in the urban and rural areas is no longer as much as it used to be. The scenario is changing rapidly due to the socio-economic transition that is taking place in the rural areas. The availability of improved modes of transport, has resulted in decreased physical activity. Better economic conditions have produced changes in dietary habits, not necessarily for the better. These conditions are conducive for the onset of diabetes in the population which already has a racial and genetic susceptibility to the disease.
Prediabetic conditions like IGT, when blood glucose levels are higher than normal but not high enough to be called diabetic, are also on the rise as is the prevalence of Metabolic Syndrome, a constellation of cardiovascular risk factors, of which high blood glucose levels and insulin resistance are components. (See boxes for details). Indians have a genetic phenotype characterised by a low body-mass index with high upper-body adiposity, a high body fat percentage and a high level of insulin resistance. the risk for diabetes and heart disease increases if the waist measurements in men are more than 90 cm and in women they are more than 80 cm.
Due to a higher degree of genetic predisposition and an equally high susceptibility to environmental insults, the Indian population faces a high risk for diabetes and its associated complications. Early diagnosis of high-risk groups and appropriate intervention by lifestyle modifications may help to find a solution for the disease burden.
The prevalence of diabetes is rising rapidly especially in the urban population in India. Since 1971 to 2000, a 10-fold increase has been observed (from 1.2 per cent to 12.1 per cent). Even cities like Chennai have shown a dramatic increase in prevalence of diabetes and IGT. The high prevalence of diabetes has remained an urban phenenomenon so far and all the previous epidemiological studies have illustrated a four-fold difference in the prevalence of diabetes between the urban and rural populations.
Our recent data has illustrated the impact of socio-economic transition occurring in rural India. It showed a three-fold rise in the prevalence of diabetes in rural southern India. The transition had occurred during a period of 14 years and the prevalence had risen from 2.4 per cent to 6.4 per cent. The contributing factors were improved socio-economic status which encompassed an increase in family income and educational status, motorised transport and a shift in the occupational structure. A similar situation has been seen in the data available from neighbouring countries such as Thailand, Malaysia, Bangladesh and Pakistan.
A recent study by the Diabetes India Group had estimated the prevalence of diabetes in urban and rural areas in India. Urban areas were designated as those having a population of 100,000, and small towns and villages with a deemed population under 100,000 were designated as rural areas. The study reported an overall diabetes prevalence of 4.3 per cent; 5.6 per cent in urban areas and 2.7 per cent in rural areas. Total prevalence of IGT was 5.2 per cent — urban being 6.3 per cent and rural 3.7 per cent.
A 4.3 per cent of overall prevalence rate for diabetes in the Diabetes India Study confirms the WHO estimate of 35 million adults with diabetes in India today. Indians show a number of peculiar features which make them highly susceptible to the disease. The high racial predisposition is evident from the studies in native Indians as well as migrant Indian populations in other parts of the world.
Nature vs nurture
Evidence has accumulated to show that the high interaction of genetic and environment influences in the Indian populations could be attributed to genetic susceptibility and low thresholds for the acquired diabetogenic factors.
Indians develop diabetes at a very young age, at least 10-15 years earlier than the White population. The National Urban Diabetes Survey in India showed that more than 50 per cent of diabetes cases had their onset below the age of 50. Indians show a significantly higher age-related prevalence when compared to the White population in the USA. Indians have several-fold higher prevalence of diabetes at all age groups in comparison with the European population as shown by the International Diabetes Epidemiology Group. It is also shown that risk of diabetes starts to increase at very low levels of BMI.
The risk of diabetes increases with small weight changes at a Body Mass Index above 22kg/m. The cut-off value for healthy BMI in Indians is below 23kg/m. It is interesting to note that the value for normal waist girth is also low in Indians (men 85cm, women 80cm). Despite having a lean BMI, an adult Indian has more chances of having abdominal obesity. The National Indian Survey showed that upper body adiposity was more common (50.3 per cent) than overweight as indicated by BMI (30.8 per cent). In Indians, central obesity shows a stronger association with glucose intolerance than generalised obesity. Studies from the UK and the USA have suggested that the insulin resistance in non-obese Asian Indians is due to the high percentage of visceral fat. This could also partly explain the higher prevalence of diabetes in them.
Low muscle mass
The higher insulin resistance may be partly due to a high body fat content seen in the Indian population. The body fat percentage of an Indian is significantly higher than his western counterpart with a similar BMI and blood glucose levels. According to a hypothesis, excess body fat and low muscle mass may explain the high prevalence of excess insulin in the blood and the high risk of Type II diabetes in Indians. Major blood vessels leading to the heart and brain are affected as well as smaller ones leading to the kidneys and eyes are also affected because of chronic tissue complications.
Internal or external migration to a more affluent environment results in metabolic changes, resulting in higher blood glucose levels and related abnormalities. The features of insulin resistance which includes upper body adiposity and high body fat percentage as well as an abnormally high level of lipids and fats circulating in the blood stream occur at a young age in Indians. Minor changes in weight or physical activity worsen insulin resistance.
The new generation of children and adolescents show unprecedented levels of obesity.
This foretells not only an epidemic of obesity to be tackled but also a great burden of treating weight-related chronic diseases such as diabetes and cardiovascular diseases. Several studies from India have highlighted that the epidemic of diabetes in urban India would become worse due to the rising trend of obesity in children. In urban southern India, 16 per cent of school children are overweight and it shows a strong association with lack of physical activity and a high social stratum. Prevalence of Type II diabetes in children is also increasing, probably due to less physical activity and altered dietary habits.
Many studies in Indians have highlighted that the risk of cardiovascular diseases is high among Indians and this could be related to the high prevalence of the metabolic syndrome (see box). An epidemiological study showed that the prevalence of metabolic syndrome among urban adults was 41 per cent.
It is interesting to note that although insulin resistance is common among Indians, it is not the major factor underlying the clustering of the cardiovascular risk factors, namely high levels of blood glucose, higher lipid levels, hypertension and upper body fat.
— Compiled by Dr A. Ramachandaran, Director, Diabetes Research Centre and MV Hospital for Diabetes, WHO Collaborating Centre for Research, Education and Training in Diabetes, Chennai, and Dr Vijay Mahajan C.M.D., Tagore Hospital & Heart Care Centre, Jalandhar