Burden of BN at the global level

Notably, from the year of 1990 to 2021, the ASRs for BN of prevalence, incidence, and DALYs all showed significant increases at the global level, with EAPCs of 0.66 (0.61 to 0.71), 0.55 (0.52 to 0.58), and 0.67 (0.62 to 0.72), respectively (Fig. 1a-c and Additional file 1). In addition, it was reported that the prevalent cases, incident cases, and DALYs cases of BN increased significantly worldwide. Specifically, in 1990, the total count of BN incident cases was 5,595,035, which rose to 8,227,657 by 2021, reflecting a percentage increase of 47%. During the period from 1990 to 2021, the number of individuals affected by BN increased by 67%, rising from 7,416,420 cases to 12,367,024 cases. Furthermore, the number of DALYs cases for BN rose from 1,564,211 in 1990 to 2,604,702 in 2021, showing a percentage change of 67% (Additional file 1 and Additional file 5). In summary, the global burden of BN has shown a persistent increasing trend from 1990 to 2021.

Fig. 1

Global maps of age-standardized rates (ASRs) per 100,000 people by BN in 2021 and estimated annual percentage changes (EAPCs) per 100,000 population by BN from 1990 to 2021. Notes: (a-c) EAPCs of ASRs for incidence, prevalence and DALYs by BN between 1990 and 2021. (d-f) ASPR, ASIR, and age-standardized DALYs of BN in 2021

Burden of BN at the SDI regional level

The global burden of BN exhibited significant regional disparities, with age-standardized incidence rates (ASIRs), age-standardized prevalence rates (ASPRs), and age-standardized DALYs closely associated with SDI levels. For example, the ASPRs for BN in 2021 demonstrated significant disparities. High SDI areas exhibited the highest ASPR for BN, recorded at 311.26 cases per 100,000 people (95% UI: 211.22 to 435.75). Conversely, Low SDI areas showed the lowest ASPR for BN, with rate of 96.69 cases per 100,000 people (95% UI: 62.85 to 140.31). Time trends in ASPRs revealed varying patterns in SDI levels, potentially indicating different stages of epidemiological transitions. The BN of Middle SDI regions exhibited the most pronounced increases in ASPRs, with EAPC of 1.42 (95% CI: 1.37 to 1.47) (Additional file 1 and Fig. 2).

Additionally, the ASRs of BN for incidence and DALYs in 2021 further underscored the existing regional disparities. High SDI regions exhibited the highest ASIR and age-standardized DALYs rate, whereas Low SDI regions demonstrated the lowest values for both metrics. The ASIR of BN in High SDI areas was 159.5 per 100,000 people (95% UI: 101.9 to 230.34). In contrast, the ASIR in Low SDI areas was 82.94 per 100,000 people (95% UI: 51.73 to 124.85) for BN. Similarly, the age-standardized DALYs rate in High SDI areas was recorded at 65.38 per 100,000 people (95% UI: 37.29 to 106.61) for BN. In Low SDI areas, the age-standardized DALYs rate was significantly lower, with rate of 20.31 cases per 100,000 people (95% UI: 11.42 to 33.98) for BN (Additional file 1 and Fig. 2). In conclusion, the BN burden in high SDI region is the highest among regions of high SDI, high-middle SDI, middle SDI, low-middle SDI and low SDI.

Fig. 2

Time trend graph of ASRs for BN from 1990 to 2021. Notes: ASIR, age-standardized incidence rate; ASPR, age-standardized prevalence rate; DALYs, age-standardized DALY rate; SDI, sociodemographic index

Burden of BN at the GBD regional level

Our findings indicated that Australasia had the highest global prevalence burden of BN in 2021. Specifically, Australasia exhibited the highest ASPR for BN, at 811.9 per 100,000 people (95% UI: 629.68 to 1041.59). The region with the second highest ASPR for BN was Western Europe, reaching 361.01 per 100,000 people (95% UI: 246.6 to 499.69). Furthermore, High-income Asia Pacific ranked third for ASPR in BN, also at 143.1 per 100,000 people (95% UI: 98.64 to 195.28). Additionally, the time trend from 1990 to 2021 indicated that BN in South Asia showed a notable increase in ASPRs, with an EAPC of 1.44 (95% CI: 1.38 to 1.50). In contrast, BN in High-income North America recorded a substantial decrease in ASPR, with an EAPCs of -0.26 (95% CI: -0.39 to -0.13) (Fig. 1e and Additional file 1).

Our analysis indicated that the incidence of BN in Australasia in 2021 was the highest globally. Specifically, the ASIR for BN in Australasia was 282.01 per 100,000 individuals (95% UI: 187.9 to 399.38). High-income North America and High-income Asia Pacific were regions with the second and third highest ASIR for BN at 178.47 per 100,000 individuals (95% UI: 111.34 to 264.22) and 160.35 per 100,000 individuals (95% UI: 100.96 to 234.27) respectively. In addition, the time trend from 1990 to 2021 indicated that East Asia exhibited the most significant growth in ASIRs for BN, with EAPC of 1.14 (95% CI: 1.07 to 1.21). Notably, ASIRs of BN did not demonstrate a downward trend in any GBD region (Additional file 1 and Fig. 1d).

In 2021, Australasia exhibited the highest age-standardized DALYs for BN. Specifically, the age-standardized DALYs rate for BN in Australasia was 170.34 per 100,000 individuals (95% UI: 106.42 to 262.05). Western Europe and High-income North America were the areas with the second and third highest age-standardized Disability-Adjusted Life Years (DALYs) rates for BN, reporting figures of 75.78 per 100,000 individuals (95% UI: 44.42 to 121.85) and 69.07 per 100,000 individuals (95% UI: 38.67 to 114.63), accordingly. Additionally, the time trend from 1990 to 2021 indicated that East Asia experienced the most significant increase in age-standardized DALYs rate for BN, with EAPC of 1.92 (95% CI: 1.81 to 2.03), accordingly. In contrast, the region that experienced the most considerable decrease in age-standardized DALYs rate for BN was High-Income North America, reporting an EAPC of -0.28 (95% CI: -0.41 to -0.15) (Additional file 1 and Fig. 1f). In addition, we also found that the ASPRs, ASIRs and age-standardized DALYs rates of BN were positively correlated with SDI in GBD regional level (Fig. 3).

Fig. 3

Regional correlations between sociodemographic index (SDI) and age-standardized rates (ASRs) of bulimia nervosa from 1990 to 2021: (a) age-standardized prevalence rate (ASIR); (b) age-standardized incidence rate (ASPR); (c) age-standardized disability-adjusted life years (DALYs) rate

Burden of BN at the National level

In 2021, the ASPRs for BN ranged from approximately 881.55 to 43.33 per 100,000 individuals in above mentioned 204 countries. Among all countries, the three countries with the highest ASPRs for BN were Australia (881.55 per 100,000 individuals; 95% UI: 691.92 to 1123.85), Monaco (677.98 per 100,000 individuals; 95% UI: 473.06 to 937.67), and Italy (478.23 per 100,000 individuals; 95% UI: 331.37 to 658.31). It was worth noting that Australia ranked among the top three countries with the highest ASPR for BN, a finding that aligned with the results of our GBD regional-level analysis. This consistency between national and regional data highlighted the significant challenges posed by BN in Australia. In addition, the time trend from 1990 to 2021 indicated that Equatorial Guinea experienced the most significant increase in ASPRs for BN conditions, with EAPC of 3.48 (95% CI: 2.86 to 4.11). In contrast, Libya experienced the most significant decrease in ASPRs for BN conditions, with EAPC of -0.72 (95% CI: -0.96 to -0.48) (Fig. 1e, Additional file 5 and Additional file 2).

In 2021, the three countries with the highest ASIRs for BN were Sweden (347.13 per 100,000 individuals; 95% UI: 214.25 to 527.83), Australia (289.42 per 100,000 individuals; 95% UI: 193.08 to 407.76), and New Zealand (247.54 per 100,000 individuals; 95% UI: 153.5 to 365.64). Furthermore, the analysis of the time trend spanning from 1990 to 2021 revealed that Equatorial Guinea saw the largest rise in ASIR for BN, demonstrating EAPC of 2.08 (95% CI: 1.79 to 2.38). Conversely, Libya faced the most notable decline in ASPR for BN conditions, reflected in EAPC of -0.37 (95% CI: -0.52 to -0.23) (Additional file 2, Additional file 5 and Fig. 1d).

In 2021, the three countries with the highest age-standardized DALYs rates for BN were Australia (185.04 per 100,000 people; 95% UI: 116.93 to 281.98), Monaco (142.15 per 100,000 people; 95% UI: 82.83 to 230.51), and Italy (100.43 per 100,000 people; 95% UI: 60.3 to 159.7). The three countries with the highest age-standardized DALYs rates for BN were identical to the three countries with the highest ASPRs mentioned previously. In addition, the time trend from 1990 to 2021 indicated that Equatorial Guinea experienced the most significant increase in age-standardized DALYs for BN, with EAPCs of 3.53 (95% CI: 2.9 to 4.17). In contrast, Libya experienced the most significant decrease in age-standardized DALYs rate for BN conditions, with EAPCs of -0.73 (95% CI: -0.97 to -0.48). The time trend results were notably consistent with the previously mentioned findings of ASPRs and ASIRs (Additional file 2, Additional file 5 and Fig. 1d-f). We also found that the ASPRs, ASIRs, and age-standardized DALYs rates of BN exhibited a positive correlation with SDI at the national level, aligning with our analysis results at the GBD regional level (Fig. 4).

Fig. 4

204 national age-standardized rates (ASRs) and sociodemographic index (SDI) correlation graphs for BN in 1990 and 2021. Notes: (a-c) the ASIR, ASPR, and age-standardized DALYs rate of BN in 1990. (d-f) the ASIR, ASPR, and age-standardized DALYs rate of BN in 2021

Age-period-cohort analysis

The findings from the analysis of the APC model demonstrated that the global trends for the prevalence, incidence, and DALYs related to BN were all showing an increase (Fig. 6). The findings of the age effect model demonstrated that the prevalence and DALYs of BN were highest among individuals aged 25 to 29 years (Rate = 398.134/100,000, 95% CI: 396.9591 to 399.3125; Rate = 84.037/100,000, 95% CI: 83.7835 to 84.2913), whereas the incidence rate peaked in those aged 15 to 19 years (Rate = 415.637/100,000, 95% CI: 414.317 to 416.9625). The findings of the period effect model demonstrated that the risks associated with the prevalence, incidence, and DALYs of BN were all experiencing an upward trend, peaking during the period of 2020–2021. Furthermore, the findings from the cohort effect analysis revealed that the occurrence, incidence, and DALYs linked to BN showed an initial rise, then a decline, and finally a resurgence. Notably, the 2015 cohort demonstrated the highest risk for prevalence, incidence, and DALYs, with RR of 1.1791 (95% CI: 1.0503 to 1.3236), 1.1581 (95% CI: 1.1086 to 1.2098), and 1.1822 (95% CI: 1.0537 to 1.3264), respectively (Additional file 3 and Fig. 5). In addition, at the global level, the burden of BN was increasing across all age groups. Notably, the prevalence of BN has risen most rapidly among individuals aged 25–29 years (0.72%, 95% CI: 0.71 to 0.73). Furthermore, the incidence of BN increased most significantly among those aged 20–24 years (0.55%, 95% CI: 0.54 to 0.56). Additionally, the DALYs associated with BN has also risen most rapidly among individuals aged 25–29 (0.72%, 95% CI: 0.71 to 0.73) (Fig. 6 and Additional file 3).

Fig. 5

Map of age, period and cohort effects

Fig. 6Cross-country inequality analysis

Globally, significant absolute and relative inequalities related to the SDI were observed in the ASPRs, ASIRs, and age-standardized DALYs rates associated with BN. From 1990 to 2021, the SII of BN ‘s ASPRs increased from − 27.6652 (95% CI: -73.1805 to 17.8501) to -40.5098 (95% CI: -85.1405 to 4.1209). In a similar manner, the RCI for ASPRs related to BN declined from − 0.0171 (95% CI: -0.0868 to 0.0526) to -0.0087 (95% CI: -0.0915 to 0.0742). Conversely, the SII for ASIRs concerning BN rose from 2.0384 (95% CI: -11.6951 to 15.7719) to 13.7049 (95% CI: 2.3937 to 25.0162). And the RCI of ASIRs for BN decreased from − 0.1135 (95% CI: -0.1918 to -0.0352) to -0.0474 (95% CI: -0.1348 to 0.0399). Furthermore, the SII regarding age-standardized DALYs rates for BN shifted from − 3.7947 (95% CI: -11.1687 to 3.5793) to 1.4976 (95% CI: -5.8955 to 8.8908). Conversely, the RCI associated with age-standardized DALYs rates for BN showed a decline from − 0.0165 (95% CI: -0.0863 to 0.0534) to -0.0068 (95% CI: -0.0895 to 0.0759) (Fig. 7 and Table 1).

Fig. 7

Cross-country inequality maps for 1990 and 2021. Notes: (a-c) Health inequality regression curves of Prevalence, Incidence, and DALYs for BN. (d-f) Concentration curves of Prevalence, Incidence, and DALYs for BN

Table 1 Extent of cross-country inequality for 1990 and 2021Projections of future global BN burden

The ASRs of incidence, prevalence, and DALYs associated with BN worldwide are expected to increase gradually. It is estimated that by 2030, the predicted ASR of BN prevalence in women will reach 200.74 per 100,000; the predicted ASR of BN prevalence in men is projected to be 128.74 per 100,000, reflecting an increase of 1.13% since 2021. Additionally, compared to 2021, the ASIR of BN was projected to increase slightly by 2030 in both sexes, with a marginally greater increase in males (0.76%) than in females (0.24%). In contrast, the predicted ASR of burden of disease attributable to DALYs of BN for women decreased slightly by 0.31% in 2030, whereas the predicted ASR for men increased slightly by 1.10% (Additional file 4 and Fig. 8).

Fig. 8

Forecast graph of prevalence, incidence and DALYs of BN from 1990 to 2030