There is a significant increase in the age standardized prevalence of DM amongst study participants observed over the last 10 years. Prevalence in this rural Bangladesh population has increased more than threefold, from 2.3% to 7.9% in the last 10 years. Further, the prevalence in this population in 2009 is higher than the prevalence found in rural China 6.1% in 2005, India 6.4% in 2004, and Turkey 7.2% in 2002 [5
]. However, the observed prevalence rate for DM reported here is lower than that of rural populations in Hawaii (20.4%) [17
]. Differences in prevalence rates may be influenced by differential methodologies applied in different populations.
The age adjusted prevalence of IFG has moderately increased in the first 5 years, from 4.6% to 5.8% and then shown minor decrease to 5.3% in 2009. In 1999, we had observed a relatively high prevalence of IFG in a population where the prevalence of DM was moderate [18
]. This may have indicated a lower prevalence of DM than IFG in this rural population of Bangladesh. The present lower prevalence of IFG could be due to vulnerability of the participants to environmental changes resulting in rapid conversion to DM. Alternatively, a rapid deterioration of susceptible normoglycemic subjects to DM could be occurring, as suggested by Mohan et al. [19
]. The trend in decreasing prevalence of IFG was also noted in an urban population of India and Mauritius [20
]. In 2009, we found a clear male predominance of IFG. This has been a consistent finding in many other populations [22
A number of structural and industrial changes have occurred in the study region between 1999 and 2009, which may have changed rural life to a more sedentary lifestyle. Household expenses have increased 50% since 1999 in this population which may be related to rising economy. Recent studies have shown an association between urbanization, economic development and increased prevalence of DM in developing countries [15
]. Mean values for BMI, WHR, and WC recorded in the studies have increased since the initial study in 1999. In between 2004 to 2009 the rate of increase in these factors has also risen when compared to the period between 1999 and 2004. The higher prevalence of DM in 2009, and the increased rate of change in risk factors in successive studies can be aligned with the increasing urbanization that has occurred in recent years.
Obesity is an established risk factor for DM. A significant association between higher BMI and the occurrence of DM was found in 2004 and 2009 study. It is of concern that mean BMI has significantly increased in last 10 years (mean BMI from 19.5 to 22.2 from the year 1999 to 2009). WHR was significantly associated with DM in men in all the studies. However, a significant association for women and WHR was only shown in 2009. The association between WHR and DM is also evident in previous studies conducted in Bangladesh [10
]. The SBP was found to be associated with DM in all surveys.
A decreasing trend in HTN among new study participants was observed. Similar to our findings, a declining trend of mean BP and prevalence of HTN has also been observed in several general populations [25
]. The reason for reduce prevalence of HTN found in our study and in both sexes is unclear. Increased awareness of HTN and increased efforts aimed at treating and controlling HTN in the last 10 years, especially among women, may be a contributing factor. The improved awareness and treatment of HTN among women has been consistently documented [29
] however the reasons for these changes are not entirely clear. Differences in health seeking behaviour, and a greater opportunity for opportunistic BP screening, due to more frequent contacts with the health care system may contribute to this gender related difference. It should be also noted that availability of low-priced antihypertensive medications and nonpharmacological measures for the prevention and management of HTN have been introduced to improve the possibilities for the effective lowering of BP in Bangladesh for the last couple of years. One recent study conducted by Centre for Control of Chronic Diseases in Bangladesh, International Centre for Diarrhoeal Disease Research, Bangladesh reported that in rural Bangladesh; village doctors (unqualified practitioners), played an almost equal role to graduate medical doctors in diagnosing HTN [31
]. Village doctors and pharmacies supply as much as 67% of the primary health care in Bangladesh [32
] as they are the preferred healthcare providers because they are perceived to be more available, accessible, and affordable than other public health care options [33
]. Longitudinal data obtained from a nationally representative sample are necessary to examine true causal relationships between BP and relevant factors.
Limitations of the study
Capillary whole blood was used in the first two studies and venous plasma blood in the third study. These methods were used to confirm the diagnosis of DM and IFG. WHO cutoff glucose values used should reflect equivalent glucose values for capillary and venous plasma blood. However, the use of point of care blood glucose meters in a multi operator setting in large populations may have adversely influenced the inter-rater reliability of the researchers' technique and glucose values in the first two studies. Health questionnaires were administered by researchers who obtained self-report information verbally and recorded it as the majority of the participants were illiterate. Therefore, the interpretation and recording of the results is a potential bias in the studies. The studies were conducted in a rural area of Bangladesh which during the 10-year period had undergone rapid urbanization and associated environmental change. Therefore the extent to which the results are generalizable or representative of other populations in Bangladesh is not known.
The prevalence of DM has continued to increase in the past 10 years in a rural population of Bangladesh. The higher prevalence of DM may also be indicative of other changing environmental factors where rapid urbanization as a pretext for economic development may have influenced individual lifestyles and dietary behaviors. The increased prevalence of risk factors for DM, amongst the study populations includes obesity and central obesity, as indicated by BMI, WC, and WHR. The significant increase of these risk indicators demonstrates the potential impact on health in a developing country. More large scale studies with control populations may be helpful in recognizing the confounding factors responsible for increased prevalence of DM and IFG in rural Bangladesh.