The all-cause and cause-specific burdens attributed to LE measured with deaths, DALYs, YLLs and YLDs are described in the following sections at the national and subnational levels in Iran. The LE cause-specific burdens are divided into two acute and chronic causes and their subcategories’ burden are discussed furtherly.

All-cause burden

From 1990 to 2019, a nearly declining trend in all-cause deaths, DALYs, YLLs, and YLDs rates attributed to LE was seen for both sexes (Fig. 1). There was a divergence between provinces for deaths, DALYs, YLLs and YLDs attributed to LE in 1990, which got more convergent in 2019 (Fig. 2).

Time trend of age-standardized attributed burden rate to lead exposure by sex in Iran, 1990–2019.

Time trend of age-standardized attributed burden rate to lead exposure at national and provincial, 1990–2019.

The age-standardized deaths rate (ASDR) per 100,000 decreased by 38.0% (95% UI 45.5–31.5) from 38.7 (27.3–52.1) in 1990 to 24.0 (16.5–32.7) in 2019. Similarly, the changes of DALYs, YLLs and YLDs in the same time interval showed a declining trend as the following: the age-standardized DALYs rate reached 454.4 (323.2–597.6) per 100,000 in 2019, indicating a − 48.9% (− 54.6 to − 44.3) decrease. The highest rate change was related to YLLs with a − 50.7% (− 56.9 to − 45.7) change; however, age-standardized YLDs rate had the lowest change in the mentioned time interval (− 36.4% (− 41.6 to − 31.0)).

The ASDR attributed to LE among 31 provinces of Iran varied from 6.1 (3.3–9.4) in Tehran to 41.8 (30.5–55.6) in Sistan and Baluchistan; Hormozgan with the highest death rate in 1990, reached 34.5 in 2019, which was nearly half of 1990. The age-standardized DALYs rate ranged from 127.8 (71.8–192.2) per 100,000 to 901.4 (673.8–1167.2) in 2019, with the same pattern for deaths: the highest and lowest provinces almost halved in 2019 compared to 1990. In terms of the age-standardized YLLs, in 2019, it ranged from as low as 90.5 (45.5–143) per 100,000 to as high as 793.9 (574.2–148.9), with a 50% decrease in the lowest and highest rates of 1990. According to the age-standardized YLDs rate in 2019, the lowest and highest were 37.3 (20.1–60.7) per 100,000 and 107.5 (68.2–156.6). Tehran and Sistan and Baluchistan were the two provinces with the lowest and the highest rates, respectively for all mentioned rates.

CVDs burden

CVDs attributed to LE accounted for an ASDR of 22.6 (15.4–31.1) in 2019, indicating a decrease (− 39.2% (− 46.6 to − 32.5)) since 1990. Similarly, the age-standardized DALYs, YLLs and YLDs revealed decreasing trends at the same period as follows; a − 50.3% (− 56.6 to − 45.3), − 51.6% (− 57.9 to − 46.5) and − 23.5% (− 30.4 to − 18.1) reduction to 391.8 (270.8–528.6), 365.5 (253.8–494.5) and 26.3 (16.1–40.0) in 2019 was reported for the changes of DALYs, YLLs and YLDs, respectively.

Among subnational provinces, the ASDR varied from 9.5 (14.9–15.9) in Tehran to 58.5 (39.6–79.8) in Hormozgan and 5.6 (2.9–8.8) in Tehran to 37.7 (27–51.1) in Ardebil in 1990 and 2019, respectively, showing a decreasing trend over time. This trend coincided, even for the DALYs, YLLs, and YLDs. Their reduced 2019 rates are as follows: DALYs spanned from 95 (47.3–149.7) to 755.6 (548.6–1000.2), YLLs from 83 (41.3–132) to 712.4 (511.6–950.4) and the YLDs from 12.0 (5.5–20.5) to 43.2 (28.6–61.9); With Tehran being the province with the lowest rate and Sistan and Baluchistan with the highest rate for all. (Supplementary Fig. 1).

Top three CVD subtypes with the highest national burden, based on DALYs rate, in 2019 are further discussed in the following (from highest to lowest) at national level, the data regarding their subnational burden is demonstrated in Supplementary File.

Ischemic heart disease

IHD bears the highest burden among CVDs subtypes. The most significant changes were for YLLs and DALYs with − 55.4% (− 61.8 to − 50.0) and − 54.8% (− 61.1 to − 49.4) downturn to 211.9 (146.5–290.4) and 217.9 (150.7–298.4) in 2019, respectively. After that, the ASDR showed a change of − 43.4% (− 50.8 to − 36.6) over this period to 12.9 (8.6–18.1); and YLDs reached 6.0 (3.5–9.6) at the end of this time interval indicating a − 10.6% (− 18.6 to − 4.0) diminution.

Stroke

The second subtype with the highest burden after IHD is stroke. The pattern of stroke rates at the national level was declining as well. The death rate decreased to 4.6 (3.0–6.4) in 2019, which showed a − 45.8% (− 54.0 to − 35.7) reduction compared with 1990. Besides, DALYs rate decreased by − 53.2% (− 60.6 to − 45.7) from 1990 to 87.5 (57.8–117.9) in 2019; YLLs rate showed a reduction almost similar to DALYs with − 55.5% (− 62.8 to − 47.6) change from 1990 to 75.4 (50.1–101.3) in 2019. The least change was for YLDs, which demonstrated a − 31.0% (− 38.8 to − 24.8) reduction over 30 years to 12.0 (7.0–18.3) in 2019.

The burden attributed to 3 stroke subtypes, including the subarachnoid hemorrhage, intracerebral hemorrhage and ischemic stroke is further described in the Supplementary File.

Hypertensive heart disease

All burden measure rates had a declining pattern at the national level during the time interval from 1990 to 2019. Deaths rate with − 13.9% (− 40.4 to 10.3), DALYs rate with − 28.0% (− 48.9 to − 8.9), YLLs with − 28.8% (− 50.4 to − 8.7) and YLDs with − 12.3% (− 26.9 to − 2.0) reduction reached to the following rates in 2019, respectively: 4.3 (1.4–9.4), 68.8 (28.5–137.5), 64.4 (26.4–129.1) and 4.4 (1.7–9.3).

CKDs burden

Investigating the burden attributed to diabetics and CKDs due to LE over 30 years demonstrated a similar downward trend: decreased age-standardized deaths, DALYs, YLLs, and YLDs rates. The ASDR, with a change of − 11.1% (− 28.2 to − 0.95) reached 1.4 (1.0–1.8) in 2019. The DALYs rate changed from − 23.3% (− 32.7 to − 0.16) to 26.6 (18.3–35.9) in 2019. Meanwhile, the YLLs rate demonstrated a similar trend and reached 21.2 (14.9–28.2) (with a percent change of − 27.1% (− 37.7 to − 19.1)), and YLDs change was slightly intangible compared to others: − 4.1% (− 14.3 to − 0.7) to 5.4 (3.2–8.4) in 2019.

Analysis of the burden at the subnational level revealed the following outcomes: the lowest and highest ASDR in 2019 was 0.6 (0.3–0.8) (Tehran) and 4.6 (3.3–6.1) (Sistan and Baluchistan), respectively; unlike other trends, the ASDR due to CKDs showed an increasing trend in some provinces like top four provinces with the highest ASDR in 2019: 1. Sistan and Baluchistan (4.1–4.6) 2. Ilam (from 2.5 to 3.1) 3. Ardebil (from 2.1 to 2.6) 4. East Azerbaijan (from 2.3 to 2.5) (Supplementary Fig. 2). This increasing trend in some provinces was also evident regarding the age-standardized DALYs, YLLs and YLDs due to CKDs. DALYs rate spanned from 10.0 (5.2–15.7) to 92.5 (66.3–121.2) in 2019. Regarding the YLLs rate, the range was from 7.5 (3.9–11.7) to 81.5 (58.1–107.7). Furthermore, the YLDs rate revealed the lowest and the highest rates of 2.6 (1.2–4.6) and 11 (6.9–16.3) in 2019; Noting that Tehran was the province with the lowest rate and Sistan and Baluchistan was the area with the highest rate for DALYs, YLLS and YLDs.

IDID burden

Acute LE causes mental disorders at an early age, and the only type involved in LE is IDID. National, the DALYs rate decreased by − 45.8% (− 54.2 to − 40.3) to 36.0 (15.3–65.3) in 2019. Among subnational provinces of Iran, the lowest to highest DALYs rate reached 22.8 (8.3–43.3) (Tehran) to 53.3 (24.5–93) (Sistan and Baluchistan) in 2019. In terms of YLDs in 2019, the total range was from 22.8 (8.3–43.3) (Tehran) to 53.3 (24.5–93) (Sistan and Baluchistan), representing a significant decrease since 2019 (Supplementary Fig. 3).

Attributed burden by SDI regions

At the SDI level, the general trend was as follows: low and low-middle provinces represented the highest rates of age-standardized deaths, DALYs, YLLs and YLDs rates due to all causes in both 1990 and 2019. On the other hand, provinces in the high SDI quintile acquired the lowest rates in both years. A closer look at the rates revealed that the highest death rates were for low-middle and low SDI regions in 1990 and 2019. In contrast, high SDI provinces revealed the lowest death rates in both years. Regarding the DALYs rate, the highest rate was seen in low and low-middle SDI regions in 1990 and the low SDI region in 2019, while the lowest rate was reported in a high SDI province in both years. YLDs rate had the same pattern as DALYs; YLLs rate’s lowest rate was the same as others in high SDI regions in both years. Concerning the highest YLLs rates, low-middle and low-SDI provinces demonstrated this feature in 1990 and 2019, respectively. The critical point comparing 1990 and 2019 is the reduction of almost all rates from 1990 to 2019 in all SDI quintiles (Fig. 3). Another noteworthy point is the improvement of SDI from 1990 to 2019, accompanying a reduction in all causes burden attributed to LE (Supplementary Figs. 4–7).

Provincial age-standardized attributed YLLs rate to lead exposure by SDI in 1990, 2000, 2010 and 2019. YLLs: Years of Life Lost; SDI: Socio-Demographic Index.

CVDs caused by LE revealed a relatively similar pattern to all-cause burden in terms of SDI; however, some subtypes, including peripheral artery disease and atrial fibrillation and flutter, revealed an increasing pattern among their deaths, YLLs and YLDs (in peripheral artery disease) rates from 1990 to 2019 (Fig. 4, Supplementary Figs. 8 and 9). Moreover, some other subtypes demonstrated different relations between the minimum and maximum rates and SDI as follows: some middle SDI provinces had the highest burden of cardiomyopathy and myocarditis and subarachnoid hemorrhage; or non-rheumatic valvular heart disease had the highest burden in high-middle SDI provinces, especially in 1990 and the lowest rate of YLDs in a low SDI province in 2019, unlike the general trend. Additionally, ischemic stroke is another example that had the highest rates of YLLs, YLDs and DALYs in high SDI provinces in 1990. Besides, RHD revealed the lowest rate of YLDs in middle and high-middle SDI provinces (Supplementary Figs. 10–14).

Distribution of provincial age-standardized burden rate due to cardiovascular diseases attributed to lead exposure by SDI quintiles, 1990 and 2019. SDI: Socio-Demographic Index.

CKDs had an almost identical pattern of deaths, DALYs, YLLs and YLDs rates to all causes burden by SDI level at the same period (Fig. 5).

Distribution of provincial age-standardized burden rate due to chronic kidney diseases attributed to lead exposure by SDI quintiles, 1990 and 2019. SDI: Socio-Demographic Index.

Attributed burden by age and sex distribution

The ASDR, DALYs and YLLs rates attributed to LE had similar age patterns, all rates increased with aging, and the rates in 2019 were lower compared to the same age group in 1990; moreover, comparing the rates between males and females in each age group, we found that males had significantly higher rates than females, illustrating a disparity in care among sexes. Regarding the YLDs rate, there was an increasing trend by aging; however, in the age group between 5 and 39 years, the rate was almost constant in 1990 and 2019. Furthermore, in all age groups, the YLDs rates were higher in 1990 compared to 2019 in both sexes, but in the age group of 70 plus, the rates were higher in 2019 than in 1990 in males, and this pattern was evident in females 75 years and older. The pattern of higher rates in males than females was obvious in the YLDs rates as well (Fig. 6).

Attributed burden rate to lead exposure by age groups and sex in Iran, 1990 vs 2019.

Regarding the CVDs burden, all rates increased by aging in both genders in both years (1990 and 2019), and it was always higher in males compared to females; moreover, the rates of each age group in 1990 was significantly higher than the same age group in 2019 for both genders. YLDs rate followed a slightly distinct pattern; it increased with aging in both genders; however, in 1990, the rate of the 80 plus age group was lower than 70–74 and 75–79 age groups for males and both genders, respectively. And it was higher in males than females in both years. Comparing 1990 and 2019 regarding YLDs rates showed higher rates in 1990 until the age of 69 years for males, and from 70 years and more, it was the other way around; however, for females, the YLDs rates were higher in 1990 until the age of 79 years and the pattern changed after the 80 years (Fig. 7).

Burden rate due to cardiovascular diseases attributed to lead exposure by age groups and sex in Iran, 1990 vs 2019.

The burden of CKDs increased with aging for both genders, which was consistently higher in males than females. Moreover, the rates in each age group were higher in 1990 than in 2019 for both genders except for the 80-plus age group, demonstrating an inverted pattern. YLDs rate had an increasing trend with aging; its rates in males were always higher or equal to females except for 35–39 and 75 plus age groups. Furthermore, the rates of YLDs in the 65-plus age group in 2019 were higher than in 1990 in the same age group for both sexes, but other ages had an inverted pattern (Fig. 8).

Burden rate due to chronic kidney diseases attributed to lead exposure by age groups and sex in Iran, 1990 vs 2019.

IDID’s DALYs rate increased until the age of 10–14 for males and 5–9 for females in 1990 and then decreased with aging; in 2019, it approximately increased until the age 20–24 and then decreased by aging. The rate was consistently higher in males than females except for the 80-plus age group in both years, which was roughly equal in both genders. Moreover, the rates demonstrated higher values in 1990 than in 2019 for both genders until the age of 69, while for the 70-plus age group, it was vice versa (Fig. 9).

Burden rate due to idiopathic developmental intellectual disability attributed to lead exposure by age groups and sex in Iran, 1990 vs 2019.