Trends and risk factors of hyperglycemia and diabetes among Kuwaiti adults: National Nutrition Surveillance Data from 2002 to 2009

Hyperglycemia and diabetes prevalences are increasing at an epidemic rate in many parts of the world, with worldwide diabetes prevalence among adults aged 20–79 years estimated to be 6.4% in 2010 and increasing to 7.7% by 2030 [1]. Diabetes is particularly prevalent in the Arabian Gulf countries; Kuwait is in the top ten countries in prevalence of diabetes [1] and diabetes accounts for an increasing number of hospital admissions [2].

This high level of diabetes is a major public health concern as it is associated with increased risk for micro- and macro-vascular complications, and of increased risk of premature death as a consequence [3‐5]. Impaired glucose tolerance (IGT) and impaired fasting glucose (IFG) are independent risk factors for diabetes [6]. In 2004, the WHO estimated that 3.4 million people globally died from consequences of high blood glucose levels [7].

One indirect factor contributing to the rise in diabetes prevalence in Arabian Gulf countries may be the increased wealth of the oil-producing countries including Kuwait as the timing of increased wealth is associated with a rapid increase in the prevalence of obesity, diabetes mellitus and cardiovascular diseases [8]. Several studies made an attempt to identify more direct risk factors for diabetes among Kuwaiti populations; however, all were based on small and selected samples [9‐12]. Further, only a few took into account potential confounding factors while examining these known risk factors [12]. In addition, there are no reports of temporal changes in the prevalence of diabetes and/or hyperglycemia among the Kuwaiti population. Kuwait instituted the Kuwait National Nutrition Surveillance (KNNS) in 1998 to monitor changes in obesity and biochemical indicators of chronic diseases including blood glucose levels. The present study was carried out to determine 8 year trends in prevalence of hyperglycemia and diabetes among Kuwaiti adults since 2002, and to examine various socio-demographic, biological and lifestyle factors that may have contributed to variation in this prevalence.

Table 1 shows the distribution of study participants by various socio-demographic, biological and lifestyle variables within study periods. Overall, females constituted a significantly higher proportion than males in all study period. For both males and females, younger people (20–29 y) constituted the highest proportion (males: 32.2 - 36.2% & females: 29.7 - 39.5%) and older people (60–69 y) the lowest proportion (males: 4.3 - 12.6% & females: 3.6 - 5.3%) in all study periods. Across study periods the prevalence of obesity varied from 31.7- 37.3% in males and 44.0-52.1% in females, of high-TC from 5.0-17.3% in males and 6.7-16.2% in females, of lower education level from 22.1-26.9% in males and 30.5-35.1% in females. Relatively more males (34.4 - 44.6%) were reported to exercise than females (19.2 - 28.6%) and only a small number of females were smokers (0.9 - 5.5%) compared to males (18.1 - 31.3%) across all study periods.

Unadjusted prevalence of IFG increased slightly with time until 2004–05 in males and then decreased to 6.0%, a 61% decrease which was significant (P<0.05), in 2008–09 (Table 2). In females, prevalence of IFG decreased with time, except for 2006–07, with a significant (P<0.05) decline to 5.3%, a 57% decrease, in 2008–09. During the 8 years (2002–09), the prevalence of IFG in males and females decreased by 7.4% and 6.8%, respectively. In both genders, prevalence of diabetes also decreased with time period. During the 8 year period (2002–09), the prevalence of diabetes in males and females fell by 9.8% and 8.9%, respectively. Prevalence of both IFG and diabetes were higher in males than females throughout the study period. However, for IFG the difference was statistically significant (P<0.05) only in 2004–05 and for diabetes, it was significant (P<0.05) in 2002–03 and 2008–09.

IFG and diabetes prevalences were also affected by age (Table 2). IFG prevalence in males increased significantly (P<0.05) from 9.1% in the 2^nd age decade to 18.9% in the 6^th. Diabetes prevalence also increased significantly with increasing age decades, reaching a maximum (40.6%) in the 6^th decade. In females, IFG prevalence increased significantly (P<0.05) from 8.2% in the 2^nd decade to 15.8% in the 6^th decade. The diabetes prevalence also increased with increasing age decades, reaching a maximum (42.4%) in the 6^th decade. There were no significant differences in the prevalences of IFG and diabetes between males and females throughout the age decades, except for diabetes in females in the 2^nd decades.

In both genders, the prevalence of IFG and diabetes increased significantly with overweight and obesity, and decreased with level of education, except for IFG in males (Table 2). Diabetes prevalence increased significantly with TC levels and decreased with any form of exercise. Both male and female smokers had lower prevalence of IFG with no significant changes in the prevalence of diabetes.

Regression coefficients (B) indicated an overall 0.125 mmol/l yearly decrease in FBG (1 mmol/L for the entire study period). Males had a greater decrease than females (1.12 vs 0.92 mmol/L); they also showed an increase in the 2002–2003 time segment followed by a marked decrease in 2006–2007 while females showed a significant time trend only within 2008–2009 (Table 3). Both males and females showed the largest decrease in the 2^nd half of the study accounting for the majority of the overall decrease (1.13 mmol/L for males and 0.87 mmol/l for the 4 year period). The largest yearly decreases for any confounder were for age >40y, particularly for males. Males with less education or who were obese also showed a greater change than the gender as a whole.

Logistic regression analysis was used to determine temporal trends in prevalence of IFG and diabetes for 2 year spans compared with 2002–03 using both unadjusted model and after adjusting for age, BMI, HC and education levels for males and females separately. Although unadjusted trends in prevalence of IFG and diabetes in both males and females were similar to that of adjusted trends, there were slightly higher OR in each study period. Therefore, we presented the adjusted OR (Table 4). Compared with 2002–03, the odds ratio (OR) of IFG in males decreased with time, and became significant (OR=0.32; 95% CI: 0.21-0.49) for 2008–09. In females, the odds of IFG decreased significantly with time period, except in 2006–07. There was a gradual significant decrease in odds of diabetes with time period in both males and females. Compared with 2002–03, the OR for diabetes in males was 0.34 (95% CI: 0.24-0.49) and in females was 0.33 (95% CI: 0.22-0.50) in 2008–09.

A second logistic regression model was carried out to determine the contribution of all the investigated risk factors of IFG and diabetes. When compared with the 2^nd age decade, the odds of having IFG increased significantly from the 4^th age decade until the 6^th decade in both males and females (Table 5). Both overweight and obese males and females were significantly more likely to have IFG than those with normal BMI. Only in females did the odds of IFG decrease significantly with increased level of education. Compared with non-smokers, the odds of IFG decreased significantly among male and female smokers. No significant association was found for either hypercholesterolemia or exercise in either gender.

Similarly, the odds of diabetes increased significantly with age from the 2^nd until the 6^th decade in both genders. Both overweight and obese males and females were significantly more likely to be diabetic than those with normal BMI. The odds of diabetes decreased significantly with increased level of education in both genders. No significant association was found with HC, exercise or smoking in either gender (Table 5).

Temporal changes in unadjusted prevalence of IFG and diabetes among Kuwaiti adults in the 8 years since 2002 show a significant decrease in both males and females. When adjusted for age, BMI, HC and education level, logistic regression analysis showed that, compared with 2002–03, both males and females remained significantly less likely to be diabetic and/or to have IFG in 2008–09 and thus confirmed the declining trends in both IFG and Diabetes among Kuwaiti adults. Time trend data for the region that can be used for comparison: a study among Iranians showed an increased trend for diabetes from 2005 to 2007 [16], as did data from Oman for 1991–2000, Saudi Arabia for 1993–2000, and UAE for 1995–2000 [8]. However, these studies represented earlier data collection period comparable to the earlier part of our study except Iranian study (2005–07).

The overall crude prevalences of IFG and diabetes were significantly higher in males than females. When the data were stratified by study periods, the prevalence of IFG in males was significantly higher than females only in 2004–05, and for diabetes, it was higher in males than in females in 2002–03 and 2008–09. The results of linear regression showed a greater decrease over time in males and closer values between the genders in 2008–2009. When logistic regression was carried out with combined genders, after adjusting for various factors, females were less likely to have IFG (OR: 0.65; 95% CI: 0.55-0.77) and/or diabetes (OR: 0.63; 95% CI: 0.53-0.75) than males. A similar gender difference in diabetes has recently been reported in Kuwaitis [12], though a lower prevalence of diabetes was reported in Kuwaiti males in an earlier study [17]. Studies from other countries in the region also reported mixed results. Men had higher prevalences of diabetes in Saudi Arabia [18], Oman [19], Yemen [20] and Jordan [21], while women had higher prevalences in Iran [16], UAE [22] and Bahrain [23]. These variabilities between countries in diabetes with gender may reflect the variation in other factors that can influence diabetes including patient identification. Further, in the present study we found a significant interaction of education level and gender with the prevalence of IFG and diabetes. Thus, it is also possible that some of the “confounders” that we adjusted for in our analysis altered the apparent gender differences.

In the present study we also explored the association of selected socio-demographic (age, education), biological (BMI and serum TC) and lifestyle (exercise and smoking) factors. As observed in earlier studies among Kuwaitis [12, 17], and as would be expected, age was found to be an important predictor of IFG and diabetes prevalence for both genders in the present study. The odds of IFG and diabetes increased with age until the 6^th decade in both genders. A similar age related change in diabetes has also been reported in other studies in the Arab Gulf region [16, 18, 22, 24].

In the present study, both overweight and obese males and females were more likely to have IFG and diabetes which are in accordance with the findings from other countries in the region [9, 18, 25‐28] where a consistently positive association of overweight and obesity with diabetes is demonstrated. It is known that adipocytes (fat cells) secrete a number of adipocyte hormones and adipokines, which may in turn increase the risk of diabetes via several pathways such as increasing insulin resistance [29].

Unadjusted prevalence of diabetes was significantly higher in both genders with moderate-HC and high-HC than in individuals with normal cholesterol level. After adjusting for confounding factors in logistic regression, the OR for diabetes in males (OR: 1.32; 95% CI: 0.95-1.83) and females (OR: 1.22; 95% CI: 0.89-1.66) were higher in those with high-HC than the subjects with normal cholesterol level, however they did not reach the level of significance.

More highly educated females were significantly less likely to have IFG or diabetes in our study, but only highly educated (undergraduate or above) males were less likely to be diabetes. An earlier study in Kuwaiti adults also showed that higher education level was associated with a significant reduction in blood glucose levels [30]. Furthermore, a lower education level has been found to be associated increased likelihood of diabetes among Bahrainis [23], Omanis [24] and Iranians [31]. It is possible that those who were more highly educated may have greater awareness of the risk factors of hyperglycemia and diabetes, and thus more likely to practice more effective preventing measures. However, higher education had no significant impact on IFG prevalence in Kuwaiti males implying that they are either less aware of the risk factors of hyperglycemia.

The prevalence rates indicate that both males and females who were exercising were possibly less likely to be diabetic than those who were not exercising. However, the results (odds ratio) were not statistically significant when adjusted for other confounders including BMI supporting excess body weight as the primary risk factor. Kuwaitis who participate in even moderate exercise have been shown to have delayed weight gain with age [32]. In a recent study we have also reported that the Kuwaiti males who exercised were significantly less likely to be obese [33]. Since we do not have any information on the duration and intensity of the exercise it is difficult interpret the present findings.

We found that both males and females who were smokers were significantly less likely to have IGF than non-smokers even when adjusted for age and BMI, though no significant association between smoking and diabetes was observed. Studies from UAE [28] and Qatar [25] showed that smokers were more likely to be diabetic than non-smokers, while a longitudinal study in Iranian adults found no association with smoking and incidence of diabetes [31]. It is important to note that most prospective studies have shown higher risk of diabetes for smokers, especially those who smoke more than 1 packet per day [34]. Unfortunately, in the present study we do not have information on the frequency/intensity and duration of the smoking. Further, it should be noted that smoking may not be a protective for IFG. Since the study is cross sectional, no cause and effect could be determined.

This study has a number of limitations. The prevalences of IFG and diabetes were estimated by single measurement of blood glucose using Accutrend GCT, which could introduce some errors. However, given that the survey included a relatively large population-based sample it is unlikely that the true prevalence will be different than that we have reported here. Further, in the present study those with known diabetes (those taking oral agents or insulin) were excluded. It is possible that this number has been increasing over time with more attention to diabetes and its treatment by Physicians, and thus our estimation of diabetes might have underestimated the prevalence in recent years, but the prevalence is still alarmingly high. Given its cross-sectional nature no causal relationship of socio-demographic and lifestyle factors with IFG and diabetes prevalence can be established. There was no information on the frequency/intensity and duration of the smoking and exercise pattern. More carefully designed studies that capture lifetime exercise, smoking and food intakes are needed to explore these potential associations between lifestyle factors and hyperglycemia. While efforts were made to obtain representative samples, the KNSS uses convenience sampling and thus the results of the present may not be representative of the wider population. Nevertheless, the main strength of this study is that it includes a relatively large population-based sample so it is likely that the true situation will not be different, on the whole, than reported here.

A decrease in the prevalence of IFG and diabetes was observed between 2002–03 and 2008–09 even when data was adjusted for known variables such as age and obesity and the suspected confounders education level, smoking and exercise. Continued monitoring is needed to determine if these decreases are persistent, as well as more detailed assessments of exercise and other confounders to determine the magnitude and duration needed to be protective. Lastly inclusion of those undergoing treatment for diabetes would facilitate evaluation of existing identification and treatment programs, and of the total prevalence of diabetes