WHAT IS ALREADY KNOWN ON THIS TOPIC

Abdominal obesity indicators, such as body mass index, waist-to-hip ratio, abdominal fat, and visceral adipose tissue (VAT), have been linked to the risk of type 2 diabetes mellitus. Nonetheless, their association with pre-diabetes is less known.

WHAT THIS STUDY ADDS

The prevalence of pre-diabetes increased as the following body composition measures increased: body mass index, total body fat mass, android fat mass, gynoid fat mass, android-to-gynoid fat ratio, and VAT mass.

The aforementioned adiposity indices showed similar associations with pre-diabetes prevalence across males and females, except for gynoid fat mass, which showed an association with pre-diabetes only among males.

Moreover, receiver operating characteristics analysis showed that VAT was the best predictor of pre-diabetes in terms of the estimated area under the curve, followed by android-to-gynoid fat ratio and android fat mass.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICYIntroduction

Unhealthy lifestyle habits such as increased consumption of an energy-dense diet and physical inactivity have led to a sharp increase in obesity incidence over recent decades. The exponential increase in obesity is strongly associated with an increased prevalence of type 2 diabetes mellitus (T2DM)1 2 and pre-diabetes3 4 worldwide. According to the International Diabetes Federation, in 2017, approximately 425 million people worldwide are living with diabetes with the number expected to exceed 629 million by the year 2045.5 In the Middle East and North African region, nearly 38.7 million people, or 9.6% of adults aged 20–79 years, have diabetes.5 Among college students and adolescents in Kuwait, the estimated prevalence of pre-diabetes is 6.3% and 33%, respectively.6 7 In the adult population, the WHO STEPS Study estimated the prevalence of pre-diabetes to be 20%8 and diabetes to be 23.1%. In a recently published study, the prevalence of pre-diabetes was estimated at 31% and undiagnosed diabetes at 4.9% among adults in Kuwait.9

Abdominal obesity is strongly associated with several metabolic syndrome components, such as abnormal lipid profile,10 hypertension (HT),11 and T2DM.12 Abdominal obesity indicators include waist-to-hip ratio, abdominal fat, trunk fat, subcutaneous adipose tissue, and visceral adipose tissue (VAT), with VAT being the most vital link with pre-diabetes incidence.13 14 Studies have shown that VAT is strongly associated with insulin resistance,15 16 T2DM, and pre-diabetes.17 VAT cells release proteins that contribute to inflammation, atherosclerosis, dyslipidemia, and HT.18 Furthermore, visceral obesity decreases insulin action via increased delivery of free fatty acids in insulin-sensitive tissues.19 20 Therefore, VAT is a crucial predictor of pre-diabetes and is strongly associated with insulin resistance.15 16 21 Studies assessing associations of VAT with diabetes and pre-diabetes have been mainly conducted on Western and Chinese populations, and such studies on Middle Eastern populations are limited.

Dual-energy X-ray absorptiometry (DXA) is a non-invasive method to measure whole-body composition, trunk, abdominal fat mass, and lean and fat tissue distribution in populations, which helps define diabetes and cardiovascular risk.22 23 The recent introduction of an algorithm that can estimate VAT from the abdominal DXA scans has made it easier to collect visceral adiposity data in extensive population-based studies, which is more cost-effective than the gold standards, CT and MRI, where the cost of running the scans is substantially higher.22 23 In addition, recent validation studies showed that the DXA-derived VAT is highly correlated with the VAT estimated from CT and MRI.24

In Kuwait, overweight and obesity affect 74.5% and 84.3% of men and women aged ≥20 years, respectively.25 Since pre-diabetes is a high-risk state for developing T2DM, metabolic syndrome, and other complications, it is essential to ascertain parameters that can identify high-risk individuals and subgroups within a population. Therefore, in this population-based cross-sectional study, we sought to estimate the prevalence of pre-diabetes and assess associations between different adiposity indices measured by DXA, such as VAT, total body fat (TBF) mass, android fat, gynoid fat, and android-to-gynoid fat ratio, with the prevalence of pre-diabetes in a sample of Kuwaiti adults. Moreover, we have stratified our analysis by sex since males and females have different body fat distribution and scientific evidence suggests that sex dimorphism in the effect of adiposity on diabetes/metabolic syndrome risk exists.

MethodsStudy participants

This population-based cross-sectional study enrolled 1240 adults between 18 and 65 years who participated in the Kuwait Wellbeing Study. The exclusion criteria included pregnancy, known diabetes, inability to walk unaided, psychosis, or terminal illness. All measurements on each individual were performed on the same day. In the current analysis, we excluded participants with undiagnosed diabetes (ie, no history of doctor-diagnosed diabetes and measured HbA1c (glycated hemoglobin) ≥6.5% (48 mmol/mol); n=56). Hence, of the total enrolled study sample, 95.5% (1184 of 1240) satisfied our inclusion criteria.

Anthropometric measurements

Trained nurses performed anthropometry measurements. Weight was measured using a calibrated scale (TANITA model BC-418 MA, Tokyo, Japan) and recorded to the nearest 0.1 kg. Height was measured by a wall-mounted stadiometer (SECA model 240, Birmingham, UK) and recorded to the nearest 0.1 cm. Both height and weight were measured without shoes and in light clothing in a standardized manner. Body mass index (BMI) was calculated as the weight in kilograms divided by the height in meters squared (kg/m2). Waist and hip circumferences were measured with a D-loop measurement tape at the midpoint between the lowest rib margin and the iliac crest and the widest level over the greater trochanters, respectively, with both measurements recorded to the nearest 0.1 cm.

DXA measurements

Total body imaging was acquired using the Lunar iDXA (GE Healthcare, Bedford, UK). Estimates of TBF mass, android fat mass, gynoid fat mass, and VAT content (mass and volume) were derived using the iDXA enCORE software (V.14.10.022; GE Healthcare). The software estimates the VAT content within the android region; the software automatically places a quadrilateral box, that is, the region outlined by the iliac crest, with a superior height equivalent to 20% of the distance from the top of the iliac crest to the base of the skull.

Daily quality assurance and quality controls were carried out during the study period before using the equipment according to standard procedures supplied by the manufacturer. The volunteers were scanned using standard imaging and positioning protocols by trained operators.26

Blood test and pre-diabetes ascertainment

Participants were asked to fast overnight for at least 10 hours. Fasting blood samples were collected upon arrival at the research unit, and HbA1c was determined using the VarianT M device (BioRad, Hercules, California, USA). Among individuals with no history of DM diagnosis and/or no history of using DM pharmacological treatments, pre-diabetes was defined as HbA1c levels of 5.7–6.4% (39–47 mmol/mol), according to the American Diabetes Association 2015 guidelines.27 Participants with HbA1c levels ≥6.5% (48 mmol/mol) were excluded from the analysis.

Statistical analysis

All statistical analyses were conducted using SAS V.9.4 (SAS Institute). The statistical significance level was set to α=0.05 for all association analyses. Descriptive analyses were conducted to estimate frequencies and proportions of categorical variables and medians and 5th and 95th percentiles of continuous variables. Prevalence of pre-diabetes, in the total population and stratified by sex, was estimated along with their binomial 95% CI. The Wilcoxon rank-sum test was used to compare the medians of quantitative variables across two groups. Correlations between body fat composition measures were tested for males and females separately using Spearman correlation coefficients.

Associations between anthropometric and DXA-derived measures of body composition with pre-diabetes status were evaluated in the total sample and stratified by sex. BMI (kg/m2) was categorized as follows: underweight/normal weight (<25.0), overweight (25.0–29.9), and obese (≥30.0). On the other hand, waist-to-hip ratio, TBF mass (kg), android fat mass (kg), gynoid fat mass (kg), VAT (kg), and android-to-gynoid fat ratio were categorized into quartiles, with the first quartile set as the reference group. To account for sex differences, quartiles of body fat composition measures were determined separately for males and females. Two analytical approaches were applied to assess the associations between the measures of body composition and pre-diabetes prevalence: the variables were treated as (1) categorical and (2) quantitative to infer the linear trends. To determine if sex is an effect modifier, statistical interactions on multiplicative scale were evaluated by including product terms (sex×BMI/waist-to-hip ratio/TBF/AF/GF/AF:GF ratio/VAT) in the regression models. Given that statistical power to detect higher-order terms is usually limited in epidemiological studies,28 interaction term p value (Pinteraction) <0.2 was considered as a ‘possible’ statistical suggestion for interaction (effect modification). Adjusted prevalence ratios (aPRs) and their 95% CIs were estimated by applying a modified Poisson regression with robust variance estimation using the GENMOD procedure in SAS V.9.4.29 In the analysis evaluating the associations in the total study sample (ie, including males and females), PRs were adjusted for sex and age. In the sex-stratified analysis, PRs were adjusted for age.

Moreover, logistic regression models were fitted to assess the discrimination ability of the different measures of body composition to accurately identify subjects with and without pre-diabetes. Receiver operating characteristics (ROC) curves, plotting sensitivity (true positives) by 1–specificity (false positives) at different cut-off points, were used to assess the discriminatory performance of models with different predictors. The area under the ROC curve (AUC) was estimated, providing a quantitative summary measure of the discriminatory performance of the fitted models. A model with an AUC of 0.5 has no discrimination value, whereas a model with an AUC of 1.0 has perfect discrimination.30 AUC and their 95% CIs were estimated for each assessed body composition measure. In addition, to test differences between the estimated AUC values, the estimated AUCs of the different measures of body fat were compared with the estimated AUC of BMI (reference measure) using the roccontrast statement in the LOGISTIC procedure in SAS V.9.4.

Results

The general characteristics of the study participants are shown in table 1. In regard to the total analytical sample (n=1184), 49.4% (n=585) were males and 50.6% (n=599) were females. The median age of the study participants was 44.0 years (5th, 95th percentile: 23.5, 60.0 years). The prevalence of pre-diabetes was estimated to be 32.6% (355 of 1088; 95% CI: 29.9% to 35.5%) in the total study sample, with males having higher pre-diabetes prevalence (35.6%, 187 of 525; 95% CI: 31.5% to 40.0%) compared with females (29.8%, 168 of 563; 95% CI: 26.1% to 33.8%; p=0.042).

Table 1

Characteristics, anthropometry, and dual-energy X-ray absorptiometry measurements of the Kuwait Wellbeing Study sample

The median BMI value of the total study sample was estimated to be 28.2 (5th, 95th percentile: 21.3, 39.6) kg/m2, with no difference between males and females. Based on BMI classification, of the total study sample, 44.4% (n=526) were overweight and 35.5% (n=420) were obese (table 1). The median waist-to-hip ratio, android fat mass, android-to-gynoid fat ratio, and VAT were higher among males than females (p<0.001, table 1). Females presented a higher TBF mass and gynoid fat mass than males (p<0.001, table 1).

Results of the correlation analyses between body fat composition measures are presented in online supplemental table 1 (males) and online supplemental table 2 (females). Overall, the magnitude and direction of correlations were similar in males and females. Although gynoid fat showed similar direction and magnitude of correlation with other body fat composition measures among males and females, an exception is the correlation between gynoid fat and waist-to-hip ratio, which showed a positive correlation in males (r=0.35, p<0.001; online supplemental table 1) and no correlation in females (r=−0.05, p=0.194; online supplemental table 2).

Associations between measures of body composition with pre-diabetes in the total study sample and stratified by sex are presented in figure 1 and table 2. An increasing pattern in the prevalence of pre-diabetes across BMI categories was demonstrated, with pre-diabetes being more prevalent among individuals in the obese category compared with those in the underweight/normal weight group (aPR=1.59, 95% CI: 1.19 to 2.12; figure 1A). Although the waist-to-hip ratio was positively associated with pre-diabetes, this association did not gain statistical significance (figure 1B). Increasing patterns in the prevalence of pre-diabetes were seen across quartiles of TBF mass (figure 1C), android fat mass (figure 1D), gynoid fat mass (figure 1E), android-to-gynoid fat ratio (figure 1F), and VAT (figure 1G). For instance, pre-diabetes prevalence was increased among participants in the highest quartile of VAT compared with those in the lowest quartile (aPRQ4 vs Q1=2.05, 95% CI: 1.49 to 2.82; figure 1G).

The measures mentioned above of body composition were associated with pre-diabetes similarly in males and females, with the exception of gynoid fat (Pinteraction=0.164, figure 1E), android-to-gynoid fat ratio (Pinteraction=0.034, figure 1F), and VAT (Pinteraction=0.094, figure 1G), which showed possible sex-related differences. In sex-stratified analysis, increased gynoid fat mass showed an association with pre-diabetes prevalence only among males (aPRQ4 vs Q1=1.71, 95% CI: 1.22 to 2.41), but not among females (aPRQ4 vs Q1=1.27, 95% CI: 0.90 to 1.78; figure 1E). Moreover, given the statistically significant ‘sex×android-to-gynoid fat ratio’ interaction term (Pinteraction=0.034, figure 1F), the association between android-to-gynoid fat ratio and pre-diabetes is stronger among females than males. In terms of VAT, the association between VAT and pre-diabetes may be stronger in males than in females (sex×VAT: Pinteraction=0.094, figure 1G).

Figure 1

Associations between general and abdominal adiposity indicators with pre-diabetes prevalence defined according to HbA1c in the total study sample and stratified by sex. (A) Body mass index is categorized by normal, overweight, and obese status, whereas (B) waist-to-hip ratio, (C) total body fat mass, (D) android fat, (E) gynoid fat, (F) android-to-gynoid fat ratio, and (G) visceral fat are ranked by quartiles. P values for linear trends are presented. Interaction term (sex×body fat measure) p values (Pinteraction) are presented to assess sex-related differences in the evaluated associations. Adjusted prevalence ratios (aPRs) along with their 95% CIs are presented. In the analysis evaluating the associations in the total study sample (ie, including men and women), PRs were adjusted for sex and age. In the sex-stratified analysis, PRs were adjusted for age. HbA1c, glycated hemoglobin.

Table 2

Associations of measures of general adiposity and abdominal adiposity with pre-diabetes prevalence defined according to HbA1c in the total study sample and stratified by sex

In the total study sample, the ROC analysis predicting pre-diabetes showed that VAT measurement had the highest estimated AUC of 0.680 (95% CI: 0.646 to 0.714, table 3), followed by the android-to-gynoid fat ratio (AUC=0.647, 95% CI: 0.613 to 0.682) and android fat (AUC=0.646, 95% CI: 0.612 to 0.680). Compared with an estimated BMI-AUC of 0.611, android fat (difference in AUC: 0.035, p=0.001) and VAT (difference in AUC: 0.069, p<0.001) were better predictors of pre-diabetes. The gynoid fat compared with BMI had lower estimated AUC for predicting pre-diabetes (difference in AUC: −0.066, p<0.001). In predicting pre-diabetes, VAT AUC compared with android fat AUC was higher (difference in AUC: 0.034, 95% CI: 0.013 to 0.055, p=0.001). Moreover, VAT AUC compared with android-to-gynoid fat ratio AUC was higher (difference in AUC: 0.033, 95% CI: 0.013 to 0.052, p=0.002). There was no difference in the AUC of android-to-gynoid fat ratio and android fat (difference in AUC: 0.001, 95% CI: −0.027 to 0.029, p=0.914).

Table 3

Estimates of area under the receiver operating characteristics curve (AUC) of body fat composition measurements for predicting pre-diabetes in the total study sample and stratified by sex

Among both males and females, VAT, android-to-gynoid fat ratio, and android fat were the best predictors of pre-diabetes. Among males, VAT (difference in AUC: 0.102, p<0.001) and android fat (difference in AUC: 0.041, p=0.004; table 3) had higher estimated AUC than BMI. Among females, compared with BMI, VAT had higher AUC (difference in AUC: 0.056, p=0.007) and gynoid fat had lower AUC (difference in AUC: −0.068, p<0.001; table 3).

Discussion

In the present study, we evaluated associations between anthropometric and DXA-derived measures of body composition with pre-diabetes in a sample of Kuwaiti adults. Body composition measures that showed associations with pre-diabetes included BMI, TBF mass, android fat mass, gynoid fat mass, android-to-gynoid fat ratio, and VAT. The aforementioned adiposity indices showed similar associations with pre-diabetes prevalence across males and females, except for gynoid fat, android-to-gynoid fat ratio, and VAT. Moreover, ROC analysis showed that VAT was the best predictor of pre-diabetes in terms of the estimated AUC, followed by android-to-gynoid fat ratio and android fat mass compared with BMI.

BMI has been extensively assessed in population-based studies as an indicator of general adiposity due to its ease of ascertainment and as a predictor of pre-diabetes status.31 32 In the current study, we observed association between BMI categories and pre-diabetes. However, as the BMI categories increased from overweight (aPR=1.33 CI: 0.99 to 1.78) to obese (aPR=1.59, 95% CI: 1.19 to 2.12), a higher prevalence of pre-diabetes was observed. In addition, the estimated average BMI in the total population was 28.2 kg/m2, and obesity prevalence was similar for males (42.4%) and females (40.7%). Another study on the Kuwaiti population had a median BMI of 28.4 kg/m2 among males and 29.1 kg/m2 among females, respectively.33 However, pre-diabetes prevalence was 20.9% for overweight and 22% for obese, compared with 32% for overweight and 41.5% of obese were pre-diabetic in the current study. In the United Arab Emirates (UAE), the prevalence of pre-diabetes among UAE nationals was 16% for both males and females; however, 33% were overweight and 49% obese.34 Since BMI is influenced by multiple body compositions, including fat mass, lean tissue, and bone mass, BMI presents certain shortcomings when predicting diabetes and pre-diabetes status.35

On the other hand, studies have shown that the waist-to-hip ratio is more strongly associated with the development of pre-diabetes and diabetes than BMI36 since the waist-to-hip ratio measures abdominal obesity, which has been proven to associate with metabolic syndromes. In a Spanish cohort, waist-to-hip ratio presented a stronger association with pre-diabetes than BMI.11 In the current study, the waist-to-hip ratio did not demonstrate a strong association with pre-diabetes prevalence in both males and females (total sample: aPRQ4 vs Q1=1.25, 95% CI: 0.96 to 1.61). These results contradict other studies that show the waist-to-hip ratio has a stronger association with pre-diabetes than BMI.

In recent years, DXA has been used as an alternative to standard epidemiological estimation techniques of obesity indices such as BMI and waist-to-hip ratio. However, waist-to-hip ratio addresses abdominal fat, including any muscle mass in the waist region. On the other hand, DXA measures regional adiposity more accurately than conventional anthropometry; in addition, the benefit of DXA is the dissection of fat compartments, including TBF, android fat, gynoid fat, and more recently, VAT.22 37 Therefore, it is advantageous in understanding the possible causes of pre-diabetes concerning the different fat compartments. In addition, compared with waist-to-hip ratio and BMI, studies have shown that DXA demonstrated more accurate cardiovascular risk estimates concerning total and regional adiposity.24 38 39 TBF is highly associated with diabetes and pre-diabetes.40 In our results (figure 1), we observed a more apparent association between TBF and a higher prevalence of pre-diabetes than observed with waist-to-hip ratio but not BMI. Compared with BMI, TBF measures the TBF and does not consider muscle and bone mass in the calculation.41

In comparison with general obesity indices (BMI and TBF), we used the ability of DXA to differentiate between various fat depots to measure android fat, gynoid fat, android-to-gynoid fat ratio, and VAT to assess which fat compartment is a better predictor of pre-diabetes. Android fat, which is measured in the abdominal region and can be described as interabdominal fat VAT,42 is generally accepted as an important risk factor for insulin resistance43; whereas gynoid fat (lower body adiposity) may lower that risk.44 In our study, android fat mass showed strong associations with pre-diabetes prevalence, and the association was similar in males and females. Interestingly, gynoid fat mass was positively associated with pre-diabetes prevalence among males but not females. The android fat PRs showed a similar association with pre-diabetes along with the four quartiles in comparison with TBF. As for gynoid fat, in general, there was a weaker association with and lower prediction (ie, AUC) of pre-diabetes in comparison with android fat, which was corroborated in a study where they found the DXA-measured android fat was highly associated with cardiovascular disease and T2DM, and showed a stronger correlation with impaired fasting glucose than gynoid fat.39 Nonetheless, in males, the gynoid fat showed similar associations with pre-diabetes to android fat, whereas in females, the association was weaker, indicating that gynoid fat is not an important risk factor for pre-diabetes in females.39 45

The presence of an association between gynoid fat and pre-diabetes in males, and the absence of such an association among females could be due to the differential correlation between gynoid fat and wait-to-hip ratio measure in males (r=0.35, p<0.001; online supplemental table 1) and females (r=−0.05, p=0.194; online supplemental table 2). Accordingly, we re-evaluated the association between gynoid fat and pre-diabetes while adjusting for the effect of waist-to-hip ratio in males and females (data not shown). Adjusting for the effect of waist-to-hip ratio did not attenuate (confound) the observed association between gynoid fat and pre-diabetes among males, nor did it induce an association among females. Hence, the observed positive association between gynoid fat and pre-diabetes in males and the lack of such an association in females is not confounded by waist-to-hip ratio.

Android-to-gynoid fat ratio has demonstrated association with an increased risk of metabolic syndrome in healthy adults.46 In addition, the android-to-gynoid ratio showed a relationship with increased risk of cardiovascular disease.39 Furthermore, from the National Health and Nutrition Examination Survey (NHANES) data, Okosun et al demonstrated that cardiometabolic dysregulation showed a stronger association with android-to-gynoid fat ratio than android fat and BMI in both males and females.47 In the current study, this is further corroborated, whereby the PRs for android-to-gynoid ratios showed a strong association with HbA1c.

Increasing proof suggests that the distribution of fat composition is critical in the development of insulin resistance.48 Studies have shown that high VAT levels increase lipolytic activity and release free fatty acids and adipokines into the portal circulation leading to hepatic insulin resistance.47 49 Therefore, it further highlights the physiological effects high VAT content has on the manifestation of metabolic syndromes. Our results showed that VAT measurements, on average, were higher in both males (1.34 kg) and females (0.67 kg) in comparison with a European cohort study of 0.542±0.451 kg and 0.258±226 kg for males and females, respectively. In addition, at the higher quartiles, Q3 (aPR=1.83 CI: 1.33 to 2.51) and Q4 (aPR=2.05 CI: 1.49 to 2.82), VAT showed strong associations with pre-diabetes. This is further verified in a cross-sectional study, whereby DXA-derived VAT showed a higher OR (10th percentile) for developing pre-diabetes and T2DM.17 Moreover, our AUC analysis showed that VAT is the best predictor of pre-diabetes in both males and females.

Our study had several strengths: a well-characterized study sample, a standardized protocol, and a large sample size. In addition, measuring different adiposity indices is a further strength of our study, which allowed us to investigate associations of different fat depots with pre-diabetes prevalence. Information bias is inevitable in epidemiological studies; however, using objective tests to ascertain pre-diabetes and adiposity indices in the current report helped minimize the effect of misclassification. Moreover, the average BMI of participants in our study (males: 28.2 kg/m2; females: 29.2 kg/m2) is similar to a prior study conducted among Kuwaiti adults (males: 28.4 kg/m2; females: 29.1 kg/m2; n=3589).33 This further indicates that our study sample is representative of the Kuwaiti population in terms of BMI, which is a main risk factor for diabetes and pre-diabetes. A limitation of the current analysis is that we did not exclude subjects with anemia, hemoglobinopathies, and other clinical conditions, which may potentially interfere with HbA1c measurements. Moreover, confounding in observational studies should not be overlooked. We did not observe associations between cigarette smoking and physical activity (ascertained as walking frequency) with body fat composition measures and pre-diabetes (data not shown). Accordingly, smoking and physical activity were not considered as possible confounders in the current analysis. Nonetheless, the assessment of physical activity was based on a single question (ie, how many times do you walk for pleasure (not as a means of transport)?), which might not capture the true physical activity state/nature. Also, information about alcohol use was not obtained in this study, which is a further limitation. It is essential to indicate that our associations represent concurrent (cross-sectional) associations and should not be interpreted as causal associations.

In our study sample of Kuwaiti adults, adiposity measurements using DXA showed strong associations with pre-diabetes. VAT and android-to-gynoid fat ratio were strongly associated with pre-diabetes prevalence in this study. Adiposity measurements using DXA demonstrated improved prediction in terms of AUC analysis for pre-diabetes relative to BMI. In general, we did not identify any pronounced differences in the association between adiposity indices and pre-diabetes in males and females. Nevertheless, increased gynoid fat in males was associated with higher pre-diabetes prevalence, whereas, in females, no association was identified. Moreover, we observed a potential sex-related effect modification of the association between android-to-gynoid fat ratio and VAT with pre-diabetes.

Data availability statement

Data are available upon reasonable request. Data are available on reasonable request from the corresponding author.

Ethics statementsPatient consent for publication

Not required.

Ethics approval

This study involves human participants. The protocol of the present study was approved by the Ethical Review Board of the Dasman Diabetes Institute, Safat, Kuwait (RA-01-2010). Written informed consent was obtained from study participants.