Impaired fasting glucose and impaired glucose tolerance in rural population of Bangladesh

The prevalence of type 2 diabetes is rapidly rising all over the world at an alarming rate. Over the past 30 years, the increase in prevalence is rising exponentially in South Asian region, data suggest a three fold increase (from 2.0 to 7.0%) in the urbanizing population of Bangladesh within 5 years. However, the prevalence of various degrees of glucose intolerance i.e. type 2 diabetes, impaired glucose tolerance and impaired fasting glucose considered vital for prevention are still unknown in this population. The objective of the study was to estimate the prevalence of impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) and type 2 diabetes (T2DM) with their demographic and anthropometric characteristics in a reasonable large sample compare to other studies conducted in Bangladesh. A random sample of 5000 rural population aged > 20 years was included in this cross sectional study. Fasting blood glucose (FBG) level was measured from 3981 individuals and 2-hr blood glucose (BG) was done on 3954 subjects, excluding known diabetic cases (n= 27). Height, weight, waist and hip circumference including blood pressure and demographic information was also collected. The prevalence of impaired fasting glucose (IFG), impaired glucose tolerance (IGT) and newly detected type 2 diabetes (T2DM) were 1.3%, 2.0% and 7.0% respectively. IFG, IGT, IFG+IGT were more prevalent in females than males. Age, body mass index (BMI), waist circumference (WC) and waist to hip ratio (WHR) were higher in glucose–intolerant subjects than in normal glucose tolerant (NGT) group. FBG and 2-hr BG values were correlated in NGT and DM subjects. Our data suggest that estimation of FBG value identifies more people with diabetes compared to 2-hr BG estimation. These findings need to be further examined in other settings with urban and rural populations for the justification of FBG for screening of diabetes in Bangladeshi population for development of intervention strategy for the prevention and management of abnormal glucose tolerance. The significance of IFG as a precursor of diabetes and CVD will become evident only from longitudinal studies in different ethnic groups.


Introduction
The prevalence of type 2 diabetes is anticipated to increase drastically during the forthcoming decades in both developed and developing countries 1 .However, the prevalence of different stages of glucose intolerance, i.e. type 2 diabetes mellitus (T2DM), impaired fasting glucose (IFG) and impaired glucose tolerance (IGT) differ distinctly between countries and populations.It has been suggested that disproportion of prevalence in the stages of glucose intolerance is related to diet, genetic susceptibility of an individual, and population age structure, stage of economic development, and level of urbanization of a country 2 .Bangladesh is a developing country with happening of recent rapid urbanization, rural to urban migration, and increase employment with some degree of economic development 3 .At the same time, the county has experienced demographic transition with slow but gradual increase in the proportion of older population 4 .
There are some population-based studies conducted in urban and rural areas of Bangladesh to estimate the prevalence of diabetes mellitus.These studies were conducted in different time points and have revealed a growing trend of diabetes prevalence ranging from 2.2 to 8.1%, both in rural and urban communities [5][6][7] .A high prevalence of diabetes and chronic heart disease (CHD) has also been reported among Bangladeshis settled in UK compare to native population 8 .Some other recent studies showed a high prevalence of diabetes, IGT and IFG in native Indians, Asian in Europe and in the USA [9][10][11] .The IFG or IGT is now considered as prediabetes and is suggested as a strong risk factor for cardiovascular diseases (CVD) 12 .
In Bangladesh, studies related to diabetes and IGT in urban areas showed different prevalence 6,13 .The results may have been influenced by different sample sizes and different cut-off values of glucose threshold for diagnosing of abnormal glucose tolerance.To the best of our knowledge a very few studies has yet been conducted in the Bangladeshi population to estimate the prevalence of glucose intolerance i.e. (IFG, IGT and T2DM,) following American Diabetes Association (ADA) or World Health Organization (WHO) criteria 14,15 .Some studies have suggested that the groups with IFG and IGT differ phenotypically any of the criteria 9,10 .It is likely that the characteristics of subjects with different categories of glucose intolerance may vary in different populations 11,12 .
Evidence suggests that risk factors for diabetes and CVD different within various regions in Pakistan, India and Bangladesh 16 .In this milieu, the purpose of the present study was to estimate the prevalence of different categories of glucose intolerance specially IFG, IGT and Type-2 DM following new WHO-1999 criteria, among the rural population of Bangladesh 15 and to identify the demographic and anthropometric characteristics of the sample population of these categories.

Materials and Methods
This analysis was carried out with the data collected from a population-based cross-sectional survey conducted in a rural community -40 km north to the Dhaka city in 2004.The details of the study population were described elsewhere 17 .In brief, the rural population was selected from a community 35 miles north of Dhaka city called 'Chandra, under Gazipur district.Ten villages were randomly selected from five areas with a population of approximately 20000 aged ≥ 20 years.All individuals were given an identification number including a household number.Among those, 5,000 populations (both males and females) were selected following a simple random procedure.Of these, 3981 subjects were participated to the study and investigated their fasting blood glucose (FBG).Two hour after BG was performed on 3954 individuals excluding known diabetic cases (n=27).
Weight, height, waist and hip circumferences were measured for the study participants in standing position wearing light cloths and no shoes.The weight was taken to the nearest 0.1 kg by a modern digital bathroom scale and the height was taken to the nearest 0.1 cm.Body Mass Index (BMI) was calculated as a ratio of weight in (kg) to height in meter squared.Waist circumference was measured at the minimum circumference between the lower border of ribs and iliac crest on the mid axillary line.Hip circumference was measured at the greatest protrusions of the buttocks just below the iliac crest.The waist hip ratio (WHR) was calculated as waist/hip circumference.
To reduce the variations in blood pressure (BP), the subjects were ensured rest and relaxation for at least 5 minutes by keeping them in sitting position before recording BP.The pressure was measured on the right arm using normal cuff for adults fitted with a standard mercury sphygmomanometer placing the stethoscope bell lightly over the pulsatile brachial artery.Blood pressure was recorded to the nearest 2mm Hg from the top of the mercury meniscus.Systolic blood pressure (SBP) was recorded at the first appearance of sound, and diastolic blood pressure (DBP) was measured at phase V, i.e. the disappearance of the sound.
Fasting capillary blood glucose was measured from all individuals (n=3,981) using HEMOCUE glucose analyzer.The machine was calibrated every day with standard glucose solution to minimize the measuring error.After estimation of FBG, all participants except the known diabetic cases (n=3954) went through 2-hr BG.

Statistical analysis
The prevalence of Diabetes, IFG and IGT was determined by simple percentages.Values are reported as mean ±SD.Group comparisons were made using t-test and χ 2 test , Pearson's correlation test was used to calculate the correlation between the variables studied.A p-value of < 0.05 was considered statistically significant.All p-values presented are two tailed.We used Stata version 7.0 (Stata Corp. 2001; Stata Statistical Software Release 7.0,College Station, TX, USA) for statistical calculations.

Ethic
Verbal consent was secured from each individual prior to inclusion in the study, as most of the participants were illiterate.They were also verbally informed of their wright to withdraw from the study at any stage or to restrict their data from the analysis.The protocol was approved by both the Norwegian and Bangladeshi ethical committee for medical research.

Results
The prevalence of IFG, IGT, IFG +IGT and diabetes were 1.3%, 2.0%, 4.3% and 7.0% respectively.IFG, IGT, IFG+IGT were more prevalent in females than males, however the difference is significant only in IFG+IGT (5.0% in females and 3.1% in males; p <0.001) group.No significant sex difference was found in diabetes or other groups.Increased BMI was observed among IGT, IFG+IGT and DM groups, and increased waist circumference was observed in IGT and DM groups (Table-I).
The mean age of the subjects increased with increasing degree of glucose intolerance in both sex.BMI, WHR and waist circumference were higher in glucose intolerant groups than in the NGT group, while the highest mean values were found in diabetes group for both sex.WHR was significantly higher in males in all groups compare to females.Waist circumference was also significantly higher in males in IFG and DM groups compare to females (Table-II).The subjects with FBG value of (5.6-6.0)mmol/l, 23.2% belongs to NGT, 74.1% belongs to IGT and 2.6% are diabetic following 2hr BG values.
Mean FBG and corresponding 2h BG values in categories of glucose tolerance in men and women.A gender differences was present in the values of NGT and DM subjects.Data for total group were used for correlation analysis The corresponding correlation (Pearson) values and significance levels between FBG and 2h BG values for NGT and DM for males, females and total subjects are (r=0.13,p<0.000; r=0.20, p <0.000; r=0.18, p=<0.000) and (r=0.78,p<0.001; r=0.85, p <0.000; r=0.81, p < 0.001) respectively (Table -IV).

Discussion
Our data showed that the prevalence of IGT was significantly higher than IFG.Prevalence of IGT was slightly higher in female but no such sex difference was observed for IFG cases.Female subjects showed significant higher prevalence of IFG+IGT whereas prevalence of diabetes did not vary between male and female subjects.However, earlier data showed higher prevalence of diabetes among female subjects 19 .Prevalence of IFG and IGT was found to vary in terms of its ascendancy across studies.IGT was found to be more prevalent compared to IFG in Mauritius 20 in USA 21 and in Pima Indians 22 .However, studies conducted in the Netherlands 23 , Finland 24 , India 9 and among Asian Indians in US 11 did not find any difference in the prevalence of IFG and IGT.Our results showed similar levels of IFG and IGT in men; however, IGT was higher in women compared to IFG, and this finding is consistent with previous studies in Bangladesh 7,13 .Sex difference in the prevalence of IGT has been reported in other countries 25 .Prevalence of IGT was found to be similar for both sexes in an urban Indian study 26 .Some other studies showed higher prevalence of IFG among men and higher prevalence of IGT among women 21,27 .
Adverse anthropometric features are more prevalent among subjects having impaired glucose regulation i.e.IFG, IGT,IFG+IGT and DM.Our data suggests that IGT and DM were more common among older participants.Similar finding on IFG was also observed in Asians Americans 11 .Contrary to this finding, a report from Austria showed that age related increase in FBG was particularly seen in subjects with IFG 28 .The diverse finding in our study and that from India compared to the studies conducted elsewhere may suggest ethnic differences.
Our data showed that the prevalence of diabetes (FBG > 6.1 mmol/l) was 6.7% while this was 3.4% following 2-hr BG values.This finding is an agreement with an Indian study where the prevalence of diabetes was 5.2% following FBG and 4.3% according to 2-hr BG threshold 29 .Furthermore, our data showed that the agreement between the two procedures (FBG and 2-h BG) for the identification of diabetic cases was around 50%.Concern was expressed previously that the IFG might not identify the same subjects as for the IGT category 29 .However, prevalence of glucose intolerance by either procedure was similar [by FBG (IFG + DM) was 12.4% or 2-h BG (IGT + DM)] was 12.6%].
In conclusion, the prevalence of glucose intolerance varied significantly depending on the procedures adopted namely FBG or 2-h BG estimates.However, concern should be raised to attempt the larger number of subjects with glucose intolerance to prevent the escalating prevalence of diabetes for medical and economical consequences.The significance of IFG and IGT as a forerunner of diabetes and CVD will become evident only from longitudinal studies in different ethnic groups.Our findings need to be further verified in other settings for the development of intervention strategy for the prevention and early management of abnormal glucose tolerance

Table I :
Prevalence of different categories of glucose tolerance and percent of sample with increased BMI, waist circumference and WHR

Table II :
Mean + SD of age, BMI, Waist, WHR by different categories of glucose tolerance, males and females

Table IV :
Mean values of FBG and corresponding 2-h BG for difference categories of glucose tolerance, male and female