Literature search
Initially, a total of 64 potential articles was retrieved. Out of these, 36 duplicate articles were removed. After careful review of the titles and abstracts, 12 articles were found irrelevant and then excluded from the process. As the result, only 16 studies were considered for full text reading. Later, six studies were excluded after full text reading because they provided no quantitative measure of the prevalence diabetes; overlapped data set; or they were not based in Afghanistan. In the end, only 10 studies were met the inclusion criteria and data were extracted accordingly for the analysis. The flow chart of study selection process is presented in Figure 1, using the PRISMA flow diagram [11].
Characteristics of the included studies
The main characteristics of selected studies are summarized in Table 1 [19-28]. All studies used cross-sectional designs and a random sampling procedure. The included studies were published between 2012 and 2017 while the period to which the data relate was from December 2011 to November 2015. The number of subjects per study ranged from 1,070 to 1,231, for a total of 11,699 subjects across studies. Six studies reported the prevalence of diabetes as an outcome of interest, and four studies reported the incidence of a composite outcome (non-communicable diseases, obesity, etc.). The existence of diabetes was tested with biological measures in all studies. Considering cut-point definitions of diabetes, eight studies used a fasting glucose level of 126 mg/dL or higher and two studies did not explicitly state the criteria that they used. Data were collected from five provinces of Afghanistan. Three studies were conducted in Kabul province [19, 20, 22], four studies in Nangarhar province [21, 23, 25, 26], and one each in Herat [27], Kandahar [24] and Balkh [28] provinces. The female proportion varied from 51.2% [24] to 66.50 % [19]. The average age of participants varied from 38.3 to 49.5 years. The percentage with hypertension ranged from 24.4% [25] to 33.14% [19], based on seven studies. The percentage of obese people varied from 16% [24] to 58.9% [28] (nine studies). The percentage of illiterate people ranged from 20.60% to 73.2% (10 studies). The percentage of smokers ranged from 5.1% to 13.7%. The percentage of overweight people ranged from 30.0% to 48.5% (nine studies).
Pooled meta-analysis
Statistical analysis of the prevalence of diabetes is described in Table 2. The pooled prevalence of diabetes was 12.14% (95% CI: 10.06–14.39, I² = 99.3%, based on 10 studies) in a total sample of 11,699 individuals. The forest plot of the prevalence estimates and their respective 95% confidence intervals (CIs) is presented in Figure 2. The funnel plot (Figure 3) showed almost no publication bias which is confirmed by the Egger regression test (p = 0.824). Furthermore, the no publication bias was confirmed by ‘Trim and Fill’ sensitivity analysis—as we did not find any hypothetical missing study. The prevalence of undiagnosed diabetes was 9.70% (95% CI: 4.99–15.74, I² = 97.5%, based on four studies) with a total sample size of 4,697 participants.
Table 2
Prevalence of diabetes and its risk factors in the adult
population of Afghanistan
Characteristic | Studies | Sample | Cases | Prevalence, % (95%CI) | I², % | Heterogeneity | P-Egger test |
Diabetes | 10 | 11,699 | 1441 | 12.14 (10.06–14.39) | 0.925 | < 0.001 | 0.824 |
Undiagnosed | 4 | 4697 | 478 | 9.70 (4.99–15.74) | 0.975 | < 0.001 | 0.1267 |
By Sex | | | | | | | 0.0278 |
Male | 6 | 3951 | 379 | 12.07 (8.98–15.55) | 0.877 | < 0.0001 | |
Female | 6 | 3095 | 508 | 12.56 (8.48–17.29) | 0.945 | < 0.0001 | |
By Age | | | | | | | |
25–34 | 4 | 1922 | 179 | 8.45 (3.65–14.97) | 0.952 | < 0.0001 | 0.0359 |
35–44 | 4 | 1179 | 164 | 13.02 (7.54–19.70) | 0.902 | < 0.001 | |
45–54 | 4 | 800 | 140 | 17.12 (9.42–26.51) | 0.907 | < 0.001 | |
55+ | 4 | 679 | 131 | 19.23 (16.20-22.44) | 0.078 | 0.354 | |
By Province | | | | | | | 0.2263 |
Nangarhar | 4 | 4650 | 536 | 11.53 (10.62–12.46) | 0 | 0.9841 | |
Kabul | 3 | 3524 | 419 | 11.81 (9.18–14.73) | 0.998 | < 0.001 | |
Balkh | 1 | 1231 | 113 | 9.18(--) | - | - | |
Herat | 1 | 1129 | 112 | 9.92(--) | - | - | |
Kandahar | 1 | 1165 | 261 | 22.40(-) | - | - | |
Heterogeneity and subgroup analysis
The pooled prevalence among females was 12.56% (95% CI: 8.48-17.29), while for males, it was 12.0% (95% CI: 8.98-15.55). When stratified by age, the pooled prevalence in age groups 25–34 years, 35–44 years, 45–54 years and 55 years and over was 8.45% (95% CI: 3.65–14.97), 13.02% (95% CI: 7.54–19.70), 17.12% (95% CI: 9.42–26.51), and 19.23% (95% CI: 16.20–22.44), respectively. The pooled prevalence in the 55 years and over age group was the highest of the four age groups, which shows that the prevalence of diabetes increases with age (Table 2).
When stratified by province, the prevalence of diabetes was highest (22.40%) in Kandahar, compared with 11.81% (95% CI: 9.18–14.73) in Kabul, 11.53% (95% CI: 10.62–12.46) in Nangahar, 9.92% in Herat, and 9.18% in Balkh. The difference in the pooled prevalence of diabetes between males and females was insignificant. There was no significant publication bias in all subgroup analyses.
The result of the univariate meta-regression analysis showed that the prevalence of diabetes increased with a mean age (β = 0.55%, 95% CI: 0.15–0.95, p=0.0074, R2= 30.64%), hypertension (β = 0.12 %, 95% CI: 0.0288–0.2068, p=0.0095, R2=38.83%) and obesity (β = 0.794%, 95% CI: 0.0094–0.1493, p=0.030, R2=38.27%). There was no significant difference by sex (male vs female), sample size, year of publication, smoking, education (illiterate versus literate) or the methodological quality of included studies.