3.1 Search results and characteristics
Our initial search found 4260 records. After removing 2130 duplicates, 2130 unique documents were reviewed for relating the titles and abstract. Then, we reviewed the full text of 350 articles. Finally, 30 articles (23 studies for GERD, 20 studies for heartburn, and 13 studies for regurgitation) were included in the study (Figure 1). The mean age of the participants (in 14 reported studies) was 39.35 years (95% CI: 34.98-43.71). Table 1 shows the characteristics of each study.
3.2 GERD prevalence and sensitivity analysis
The daily, weekly, monthly, and overall prevalence of GERD symptoms in Iranian population was 5.64% (95% CI: 3.77%-8.35%; heterogeneity: I2= 98.76%, P< 0.001; N= 66,398), 12.50% (95% CI: 9.63%-16.08%; heterogeneity: I2= 99.50%, P< 0.001; N= 110,388), 18.62% (95% CI: 12.90%-26.12%; heterogeneity: I2= 99.66%, P< 0.001; N= 70,749) and 43.07% (95% CI: 35.00%-51.53%; heterogeneity: I2= 99.66%, P< 0.001; N= 73,189), respectively (Figure 2).
The sensitivity analysis for prevalence of all types GERD symptoms by removing a study showed that the overall result is still powerful (Figure 1-Supplement).
3.3 Subgroup analysis of GERD
The subgroup analysis for the daily, weekly, monthly, and overall prevalence of GERD symptoms is shown in Table 2. For the daily prevalence of GERD, the subgroup analysis of the study population (P< 0.001) and the data collection method (P = 0.019) were significant. For the weekly prevalence of GERD, subgroup analysis of the area (P = 0.001) and study population (P< 0.001) were significant. For the monthly prevalence of GERD, the subgroup analysis of the population was significant (P = 0.001). For the overall prevalence of GERD, the subgroup analysis of the area (P< 0.001), the study population (P< 0.001) and the quality of studies (P = 0.005) were significant. Other variables were not significant.
3.4 The prevalence of GERD by gender
The daily, weekly, monthly, and overall prevalence of GERD symptoms in Iranian males was 5.72% (95% CI: 3.41%-9.46%; heterogeneity: I2= 97.44%, P< 0.001; N= 26,004), 11.38% (95% CI: 6.69%-12.01%; heterogeneity: I2= 97.80%, P< 0.001; N= 19,453), 15.68% (95% CI: 10.67%-22.45%; heterogeneity: I2= 98.15%, P< 0.001; N= 8,865) and 39.26% (95% CI: 32.35%-46.62%; heterogeneity: I2= 99.04%, P< 0.001; N= 31,704) (Figure 2-suplementary).
The daily, weekly, monthly, and overall prevalence of GERD symptoms in Iranian females was 7.88% (95% CI: 3.67%-16.11%; heterogeneity: I2= 98.56%, P< 0.001; N= 31,588), 12.81% (95% CI: 9.47%-17.10%; heterogeneity: I2= 98.04%, P< 0.001; N= 19,380), 16.96% (95% CI: 13.17%-21.56%; heterogeneity: I2= 98.17%, P< 0.001; N= 21,567), 17.07% (95% CI: 13.20%-21.56%; heterogeneity: I2= 96.26%, P< 0.001; N= 8,563), and 45.51% (95% CI: 38.22%-52.99%; heterogeneity: I2= 98.99%, P< 0.001; N= 38,252) (Figure 3-suplementary).
Odds ratio (OR) for the prevalence of daily, weekly, monthly, and overall prevalence of GERD in women compared to men in Table 2 shows that there is a significant difference only in the daily prevalence of GERD (P = 0.003).
3.5 Meta-regression and publication bias for prevalence of GERD
The meta-regression model based on years of study for GERD prevalence revealed that the meta-regression coefficient for daily, weekly, monthly, and overall prevalence of GERD was (-0.022, 95% CI -0.132 to 0.087, P = 0.688), (0.025, 95% CI -0.410 to 0.092, P = 0.450), (0.0140, 95% CI -0.057 to 0.085, P=0.700) and (0.038, 95% CI -0.081 to 0.085, P = 0.104), respectively (Figure 3).
Regarding publication bias, the significance level of Egger and Begg's tests was (Egger=0.024 and Begg's=0.152), (Egger=0.628 and Begg's=0.624), (Egger< 0.001 and Begg's=0.533) and (Egger=0.002 and Begg's=0.754) for the daily, weekly, monthly, and overall prevalence of GERD, respectively (Figure 4-suplementary).
3.6 Heartburn prevalence and sensitivity analysis
The daily, weekly, monthly, and overall prevalence of heartburn in Iranian population was 2.46% (95% CI: 0.93%-6.39%; heterogeneity: I2= 99.15%, P< 0.001; N= 18,774), 9.52% (95% CI: 6.16%-14.41%; heterogeneity: I2= 99.58%, P< 0.001; N= 54,125), 8.19% (95% CI: 2.42%-24.30%; heterogeneity: I2= 99.76%, P< 0.001; N= 19,363) and 23.20% (95% CI: 13.56%-36.79%; heterogeneity: I2= 99.77%, P< 0.001; N= 26,543), respectively (Figure 4).
The sensitivity analysis for prevalence of daily, weekly, monthly, and overall prevalence of heartburn by removing a study showed that the overall result is still powerful (Figure 5-Supplement).
3.7 Subgroup analysis of heartburn
For the daily prevalence of heartburn, the subgroup analysis of the area (P< 0.001), study population (P< 0.001) and the quality of studies (P< 0.001) were significant. For the weekly prevalence of heartburn, subgroup analysis of the area (P = 0.001), study population (P< 0.001) and year of study (P= 0.021) were significant. For the monthly prevalence of heartburn, the subgroup analysis of the population was significant (P = 0.044). For the overall prevalence of heartburn, the subgroup analysis of the area (P= 0.019), and the study population (P< 0.001) were significant. Other variables were not significant.
3.8 The prevalence of heartburn by gender
The daily, weekly, monthly, and overall prevalence of heartburn in Iranian males was .61% (95% CI: 0.59%-10.75%; heterogeneity: I2= 98.19%, P< 0.001; N= 4,778), 5.68% (95% CI: 1.81%-16.44%; heterogeneity: I2= 98.69%, P< 0.001; N= 7,257), 5.93% (95% CI: 3.93%-8.84%; heterogeneity: I2= 89.65%, P< 0.001; N= 4,788) and 16.54% (95% CI: 10.9%-24.28%; heterogeneity: I2= 96.43%, P< 0.001; N= 1,788) (Figure 6-suplementary).
The daily, weekly, monthly, and overall prevalence of heartburn in Iranian females was 2.90% (95% CI: 0.36%-19.95%; heterogeneity: I2= 98.45%, P< 0.001; N= 2,803), 6.89% (95% CI: 2.96%-15.21%; heterogeneity: I2= 98.02%, P< 0.001; N= 5,171), 9.90% (95% CI: 6.45%-14.90%; heterogeneity: I2= 92.19%, P< 0.001; N= 3,183), 22.28% (95% CI: 12.31%-36.91%; heterogeneity: I2= 98.02%, P< 0.001; N= 2,803) (Figure 7-suplementary).
OR for the prevalence of daily, weekly, monthly, and overall prevalence of heartburn in women compared to men in Table 2 shows that there is a significant difference in the weekly (P= 0.015), monthly (P< 0.001) and overall (P = 0.008) prevalence of heartburn.
3.9 Meta-regression and publication bias for prevalence of heartburn
The meta-regression model based on years of study for heartburn prevalence revealed that the meta-regression coefficient for daily, weekly, monthly, and overall prevalence of heartburn was (0.136, 95% CI -0.241 to 0.514, P = 0.478), (0.109, 95% CI 0.013 to 0.205, P = 0.025), (0.205, 95% CI 0.004 to 0.405, P=0.044) and (0.047, 95% CI -0.103 to 0.198, P = 0.539), respectively (Figure 5).
Regarding publication bias, the significance level of Egger and Begg's tests was (Egger=0.028 and Begg's=0.707), (Egger=0.118 and Begg's=0.392), (Egger=0.005 and Begg's=0.548) and (Egger=0.025 and Begg's=0.754) for the daily, weekly, monthly, and overall prevalence of heartburn, respectively (Figure 8-suplementary).
3.10 Regurgitation prevalence and sensitivity analysis
The daily, weekly, monthly, and overall prevalence of regurgitation in Iranian population was 4.00% (95% CI: 1.88%-8.32%; heterogeneity: I2= 99.03%, P< 0.001; N= 18,774), 9.79% (95% CI: 5.99%-15.60%; heterogeneity: I2= 99.55%, P< 0.001; N= 41,140), 13.76% (95% CI: 6.18%-44.31%; heterogeneity: I2= 99.73%, P< 0.001; N= 19,363) and 36.53% (95% CI: 19.30%-58.08%; heterogeneity: I2= 99.86%, P< 0.001; N= 21,174), respectively (Figure 6).
The sensitivity analysis for prevalence of all types regurgitation symptoms by removing a study showed that the overall result is still powerful (Figure 9-Supplement).
3.11 Subgroup analysis of regurgitation
For the daily prevalence of regurgitation, the subgroup analysis of the area (P< 0.001), study population (P< 0.001), the quality of studies (P< 0.001) and the data collection method (P = 0.019) were significant. For the weekly prevalence of regurgitation, subgroup analysis of the area (P = 0.001) was significant. For the monthly regurgitation of heartburn, the subgroup analysis of the population was significant (P< 0.001). For the overall prevalence of regurgitation, the subgroup analysis of the area (P= 0.019), and the study population (P= 0.019) were significant. Other variables were not significant.
3.12 The prevalence of regurgitation by gender
The daily, weekly, monthly, and overall prevalence of regurgitation in Iranian males was 3.59% (95% CI: 1.17%-10.47%; heterogeneity: I2= 97.58%, P< 0.001; N= 4,788), 7.93% (95% CI: 4.55%-13.46%; heterogeneity: I2= 95.25%, P< 0.001; N= 5,008), 10.15% (95% CI: 5.61%-17.70%; heterogeneity: I2= 97.28%, P< 0.001; N= 4,788) and 28.00% (95% CI: 24.66%-31.60%; heterogeneity: I2= 81.76%, P< 0.001; N= 4,788) (Figure 10-suplementary).
The daily, weekly, monthly, and overall prevalence of regurgitation in Iranian females was 4.63% (95% CI: 0.78%-23.11%; heterogeneity: I2= 98.76%, P< 0.001; N= 2,803), 6.81% (95% CI: 3.64%-12.41%; heterogeneity: I2= 94.86%, P< 0.001; N= 3,183), 5.23% (95% CI: 1.11%-21.34%; heterogeneity: I2= 98.49%, P< 0.001; N= 2,803) and 30.59% (95% CI: 17.89%-47.14%; heterogeneity: I2= 98.29%, P< 0.001; N= 2,803) (Figure 11-suplementary).
OR for the prevalence of daily, weekly, monthly, and overall prevalence of regurgitation in women compared to men in Table 2 shows that there is no significant difference in the prevalence of regurgitation.
3.13 Meta-regression and publication bias for prevalence of regurgitation
The meta-regression model based on years of study for heartburn prevalence revealed that the meta-regression coefficient for daily, weekly, monthly, and overall prevalence of heartburn was (0.091, 95% CI -0.206 to 0.390, P = 0.546), (0.081, 95% CI -0.029 to 0.192, P = 0.149), (0.162, 95% CI 0.027 to 0.297, P=0.018) and (0.193, 95% CI 0.062 to 0.072, P = 0.001), respectively (Figure 7).
Regarding publication bias, the significance level of Egger and Begg's tests was (Egger=0.060 and Begg's=0.452), (Egger=0.221 and Begg's=0.999), (Egger=0.011 and Begg's=0.999) and (Egger=0.074 and Begg's=0.763) for the daily, weekly, monthly, and overall prevalence of heartburn, respectively (Figure 12-suplementary).