Table 1 Data extraction of the 27 studies in the systematic review with a cohort study design

Fang et al. (2020) [21]

(panel study)

The mean ± SD 72-hour PM_2.5 concentration was 54.57 ± 46.21 µg/m³, with an IQR of 31.43 µg/m³.

The average PM_2.5 concentration far exceeded the WHO air quality guidelines.

Chinese persons residing in Jinan (n = 71) aged between 60 and 69 years with a mean ± SD age of 65.1 ± 2.8 years.

Study period: Sept. 2018 – Jan. 2019

An IQR increment of total PM_2.5 concentration was significantly associated with a 3.27% reduction in eGFR (p < 0.05) for the lag period of 0 – 24 h.

Blum et al. (2020) [22]

(prospective cohort study)

The median annual average ± SD PM_2.5 concentrations were 15.3 ± 1.0 µg/m³, 12.2 ± 0.7 µg/m³, 9.4 ± 0.8 µg/m³, and 14.6 ± 1.2 µg/m³ for Forsyth County, Jackson, Minneapolis, and Washington County, respectively.

The average PM_2.5 concentration exceeded the newly set WHO air quality guidelines for all counties.

Participants from the Atherosclerosis Risk in Communities cohort (n = 10,997). Mean ± SD age at the last visit was 63 ± 6 years.

Study period: 1996 – 2016

No significant association between PM_2.5 exposure and eGFR could be shown at baseline.

A higher annual average PM_2.5 exposure was associated with increased albuminuria (p ≤ 0.001) and a higher risk of developing CKD (p < 0.05).

Mehta et al. (2016) [23]

(prospective cohort study)

The mean average ± SD 1-year PM_2.5 exposure levels were 11.4 ± 1.0 µg/m³ at the first visit and 10.5 ± 1.4 µg/m³ across all visits.

The average PM_2.5 concentration exceeded the WHO air quality guidelines.

Participants from the Veterans Administration Normative Aging Study (n = 669) with a mean ± SD age of 73.5 ± 6.8 years.

Study period: 2000 – 2011

One-year PM_2.5 exposure was significantly (p < 0.05) associated with reduction in eGFR and an additional annual decrease in eGFR.

Li A. et al. (2021) [24]

(prospective cohort study)

For PM_2.5, the 7-day moving average concentrations were 84.8 ± 38.9, 55.5 ± 29.6, and 40.1 ± 20.5 µg/m³ at the first through third visit, respectively. These concentrations far exceeded the air quality guidelines set by the WHO.

Participants residing in Beijing, China (n = 169) with an average ± SD age of 64.0 ± 8.7 years.

Study period: Nov. 2016 – 2018

No associations could be found between PM_2.5 exposure and eGFR or UACR (p > 0.05).

Feng Y.M. et al. (2021) [25]

(prospective cohort study)

The median PM_2.5 level was 13.1 µg/m³ (5th to 95th percentile interval, 12.4 to 15.3 µg/m³). The levels exceeded the air quality guidelines set by the WHO.

Flemish residents (Belgium) (n = 820 at baseline and n = 653 at follow-up) with a mean follow-up of 4.7 years.

Study period: 2005 – 2009

No renal outcome (eGFR, serum creatinine, microalbuminuria, and CKD) could be associated to PM_2.5 exposure levels when observing only the baseline participation, only the follow-up participation, or a combination (p > 0.05).

Li Q. et al. (2021) [26]

(prospective cohort study)

The median PM_2.5 exposure was 61.0 µg/m³ (IQR: 49.0 to 75.5 µg/m³) of all participants. The mean ± SD PM_2.5 exposure was 60.9 ± 15.7 µg/m³.

The PM_2.5 levels exceeded by far the air quality guidelines set by the WHO.

Chinese residents of Han ethnicity (n = 1,280,750 females and n = 1,256,297 males) who were ≥ 18 to ≤ 45 years of age.

Study period: Jan. 2013 – Oct. 2014

Significant differences in serum creatinine and eGFR could be observed for each 10 µg/m³ increment of PM_2.5 exposure. The association was higher in females compared to males (p < 0.05).

Gao et al. (2021) [27] (prospective cohort study)

The average mean ± SD 28-day PM_2.5 levels were 9.27 ± 3.08 µg/m³.

The average PM_2.5 concentration exceeded the WHO air quality guidelines.

Participants form the Veterans Administration Normative Aging Study (n = 808; study visits = 2,466) with a mean ± SD age of 75.7 ± 7.2 years.

Study period: 1998 – 2016

Short-term (28-day) exposure to ambient PM_2.5 could be robustly associated to a decrease in eGFR (p < 0.001), but could not be associated to serum uric acid, blood urea nitrogen, and odds of CKD (p ≥ 0.06).

Xu et al. (2016) [30]

(cohort study)

The 3-year average PM_2.5 exposure varied, ranging from 6 – 114 µg/m³ with a mean of 52.6 µg/m³.

The average PM_2.5 concentration far exceeded the WHO air quality guidelines.

Patients providing a renal biopsy in 938 hospitals spanning 282 cities in China (n = 71,151). Of the total participants, the mean ± SD age was 37.3 ± 15.9 years.

Study period: 2004 – 2014

 A 10 µg/m³ increment in PM_2.5 exposure was associated with 14% higher odds for membranous nephropathy at PM_2.5 > 70 µg/m³; no association was shown at PM_2.5 < 70 µg/m³. The annual increase in risk for MN was greater in cities with higher slopes of PM_2.5 exposure.

A higher 3-year average PM_2.5 concentration was associated with an increased risk of membranous nephropathy.

Lin S.Y. et al. (2018) [31]

(cohort study)

The daily average ± SD PM_2.5 amounted to 34.8 ± 8.76 µg/m³.

PM_2.5 exposure levels were divided into 4 quartiles: Q1 (<29.5 µg/m³), Q2 (29.5 – 33.2 µg/m³), Q3 (33.3 – 41.2 µg/m³), and Q4 (>41.2 µg/m³).

The average PM_2.5 concentration far exceeded the air quality guidelines set by WHO.

Persons registered in the Longitudinal Health Insurance Database (n = 161,970) in Taiwan with a mean ± SD age of 40.5 ± 14.6 years.

Follow-up time (mean ±SD): 11.7 ± 0.99 years

Study period: Jan. 2000 – Dec. 2011

Increasing quartile concentrations of PM_2.5 were associated with an increased risk of nephrotic syndrome (p ≤ 0.05). Similar results were obtained when stratified by the follow-up period (≤ 6 years).

Bowe et al. (2020) [34]

(prospective cohort study)

PM_2.5 exposure levels were divided into 4 quartiles: Q1 (5.0 – 10.1 µg/m³), Q2 (10.2 – 11.8 µg/m³), Q3 (11.9 – 13.7 µg/m³), and Q4 (13.8 – 22.1 µg/m³).

The PM_2.5 concentrations of all quartiles exceeded the new WHO air quality guidelines.

War veterans with diagnosed diabetes mellitus (n = 2,444,157) from the United States with a median (IQR) age of 62.5 (54.7 to 71.8) years.

Follow-up time (median): 8.5 years

Study period: Oct. 2003 – Sept. 2012

Adjusted incidence rates of kidney disease outcomes were elevated across increasing PM_2.5 quartiles.

A 10 µg/m³ increment in PM_2.5 was individually associated with increased odds of diabetes and increased risk of kidney disease outcomes. Diabetes may be a mediator in the relationship between PM_2.5 exposure and kidney disease outcomes.

Chin et al. (2018) [35]

(cohort study, longitudinal analysis)

The mean ± SD PM_2.5 exposure level was 34.1 ± 6.0 µg/m³.

PM_2.5 exposure levels were subdivided into quartiles: Q1 (27.7 µg/m³), Q2 (data not shown), Q3 (38.8 µg/m³), and Q4 (data not shown).

The average PM_2.5 concentrations far exceeded the WHO air quality guidelines.

Patients diagnosed with diabetes mellitus type II (n = 812) from Taiwan with a mean ± SD age of 55.4 ± 8.4 years.

Study period: 2003 – 2012

The annual increase of ACR was positively associated with PM_2.5 exposure (p < 0.05).

A more rapid progression of microalbuminuria was seen in patients exposed to higher levels of PM_2.5.

Chan et al. (2018) [37]

(cohort study, longitudinal analysis)

The overall average mean ± SD for PM_2.5 exposure was 27.1 ± 8.0 µg/m³ with an IQR of 10.4 µg/m³, exceeding the air quality guidelines set by WHO.

Baseline PM_2.5 exposure increased slightly from 2001 to 2004 and then declined, but remained relatively stable from 2005 to 2011.

General Taiwanese adult population with a mean ± SD age of 38.9 ± 11.3 years (n = 100,629). Of the participants, 4,046 incident CKD cases developed during the follow-up period of 10 years.

Study period: 1994 – 2014

Higher levels of PM_2.5 exposure was associated with a higher risk of developing CKD (p < 0.05).

A significant dose-response trend was observed, with a 6% increased risk of developing CKD for a 10 µg/m³ increment of PM_2.5 (p < 0.05).

Lin S.Y. et al. (2020) [39]

(prospective nation-wide cohort study)

The inverse distance weighing method was used to calculate annual average PM_2.5 exposure and to estimate the annual exposure for each patient (average ± SD: 34.8 ± 8.76 µg/m³).

PM_2.5 exposure was divided into 4 quartiles: Q1 (<29.5 µg/m³), Q2 (29.5 – 33.3 µg/m³), Q3 (33.3 – 41.2 µ/m³), and Q4 (≥41.2 µg/m³).

An IQR value was set at 8.3 µg/m³ PM_2.5.

The average PM_2.5 concentration exceeded the air quality guidelines set by WHO.

Adult participants with a mean ± SD age of 40.3 ± 14.5 years residing in Taiwan (n = 161,970).

Median (IQR) follow-up time: 11.9 (11.8 – 12) years

Study period: 1998 – 2011

 A higher risk of CKD was associated with increasing levels of PM_2.5 exposure (p < 0.001).

The risk of ESRD development was increased with PM_2.5 exposure in a similar trend as the increased risk of developing CKD (p ≤ 0.01).

Ran et al. (2020a) [40]

(prospective cohort study)

The annual mean ± SD concentration of PM_2.5 exposure level was 37.8 ± 2.9 µg/m³ with an IQR of 4.0 µg/m³ at the baseline of the study.

The average PM_2.5 concentration exceeded the WHO air quality guidelines by almost four-fold.

Adults > 65 years from the Hong Kong Elderly Health Service cohort (n = 66,820) of whom 902 participants developed CKD (mean ± SD age: 72.8 ± 6.0 years).

Study period: 1998 – 2010

PM_2.5 exposure was associated with the hazard of developing CKD in the presence of hypertension.

A higher risk of all-cause mortality was associated with PM_2.5 exposure.

An increased risk for renal failure and mortality risk of renal failure was shown in association with an IQR increment of PM_2.5; the latter for CKD patients with existing hypertension.

Furthermore, concentration-response relationships of all-cause and renal failure mortality risks associated with PM_2.5 were demonstrated.

Jung et al. (2021) [43]

(retrospective cohort study)

The mean PM_2.5 levels were 24.84 and 24.37 µg/m³ for CKD patients who died and survived during follow-up, respectively.

Both mean values exceeded the air quality guidelines set by the WHO.

A subset of the South Korean population (n = 18,717) consisted of CKD patients (whom had PM_2.5 exposure data available) with a mean ± SD age of 57 ± 17 years with a follow up of mean ± SD of 4.10 ± 2.51 years.

Study period: 2001 – 2015

 A significant effect was observed between PM_2.5 levels and mortality in CKD patients (p = 0.019). Long-term exposure was shown to have negative effects on mortality in CKD patients.

Ghazi et al. (2021) [44]

(cohort study)

The median PM_2.5 concentration was 10.1 µg/m³ for the overall cohort.

At baseline, PM_2.5 levels were <9.5 µg/m³, 9.5 to 10.1 µg/m³, 10.1 to 10.7 µg/m³, and ≥10.7 µg/m³ for Q1, Q2, Q3, and Q4, respectively.

Adult patients (≥18 years old; n = 113,725) with an average ± SD age of 50 ± 18 years (Minnesota, USA).

Study period: Jan. 2012 – Apr. 2019

11% of the population had CKD.

Increased risk and greater odds for developing CKD was observed for patients who had elevated levels of PM_2.5 exposure (p < 0.05).

Bo et al. (2021) [46]

(cohort study)

The 2-year average ± SD PM_2.5 levels amounted to 26.7 ± 7.7 µg/m³.

These levels exceed the air quality guidelines set by the WHO.

Taiwanese residents (n = 163,197) with a mean ± SD age of 38.4 ± 11.6 years at recruitment. The average follow-up period was 5.1 years (range from 1.0 to 7.4 years).

Study period: 1996 – 2016

 A linear concentration-response relationship was shown between average PM_2.5 levels and incidence of CKD. Each 5 µg/m³ decrease in ambient PM_2.5 concentration could be associated with a reduced risk of CKD development (p < 0.001).

Zeng et al. (2021) [47]

(longitudinal cohort study)

The mean ± SD concentration of PM_2.5 amounted to 26.8 ± 7.8 to 7.9 µg/m³ (SD for incidence of eGFR decline ≥30% and CKD incidence, respectively).

The air quality guidelines set by the WHO were exceeded.

Taiwanese participants (total of n = 108,615 for eGFR and n = 104,092 for CKD analysis) were included to investigate the effect on incidence of eGFR decline ≥30% and CKD incidence, with a mean ± SD follow-up period of 6.7 ± 3.2 years.

Study period: 2001 – 2016

 A moderate to high exposure to PM_2.5 was associated with a higher risk of incident eGFR decline ≥30% and incident CKD (p < 0.001).

Associations were also positive per 10 µg/m³ increment of PM_2.5 (p < 0.001).

Wu et al. (2020) [50]

(prospective cohort study)

PM_2.5 exposure was divided into 4 quartiles: Q1 (11.71 – 28.69 µg/m³), Q2 (28.69 – 30.16 µg/m³), Q3 (30.16 – 39.96 µ/m³), and Q4 (39.96 – 46.63 µg/m³), with all quartiles exceeding the WHO air quality guidelines.

An IQR value was set at 11.31 µg/m³.

Adults registered in the National Health Insurance Research Database from Taiwan (n = 623,894). Of the participants, 1,945 subjects developed ESRD during the study period.

Study period: 2003 – 2012

 A significant positive association was found between PM_2.5 exposure and incidence of ESRD (p < 0.05).

Participants in the highest quartile of exposure to PM_2.5 had a significantly higher risk of developing ESRD and a higher cumulative incidence of ESRD compared to participants in the 1st quartile (p < 0.05).

Bowe et al. (2018) [51]

(prospective cohort study)

PM_2.5 exposure was divided into 4 quartiles: Q1 (5.0 – 9.1 µg/m³), Q2 (9.2 – 11.0 µg/m³), Q3 (11.1 – 12.6 µ/m³), and Q4 (12.7 – 22.1 µg/m³).

Two of the quartiles had average PM_2.5 concentrations that exceeded the WHO air quality guidelines.

War veterans (USA) with a median age (IQR) of 62.46 (54.68 – 71.78) years (n = 2,482,737) with a median follow-up period of 8.52 years.

Study period: Oct. 2003 – Sept. 2012

An increased risk of incident eGFR <60mL/min/1.73 m², an eGFR decline ≥30%, incident CKD, and an increased risk of developing ESRD was shown for 10 µg/m³ increment in PM_2.5 exposure (p ≤ 0.05).

A linear relationship was observed between PM_2.5 exposure and risk of eGFR decline ≥ 30%.

Ran et al. (2020b)[52]

(retrospective cohort study)

Median value for PM_2.5 exposure was 35.78 µg/m³ at the baseline study period (1998 – 2000).

An IQR of 3.22 µg/m³ PM_2.5 was identified.

The median PM_2.5 concentration far exceeded the WHO air quality guidelines.

Elderly population (Hong Kong) with a mean ± SD age of participants of 72.0 ± 5.6 years (n = 61,447).

Study period: 1998 – 2010

PM_2.5 exposure was associated with a higher risk of renal failure mortality in the entire cohort (p < 0.01) and in the subgroup analysis of incident CKD (p ≤ 0.01).

An IQR increment of PM_2.5 led to elevated mortality risk of AKI, but not CKD or unspecified renal failure.

Lin Y.T. et al. (2020) [53]

(prospective cohort study)

PM_2.5 exposure was divided into 4 quartiles: Q1 (<32.08 µg/m³), Q2 (32.08 – 36.27 µg/m³), Q3 (36.27 – 39.88 µ/m³), and Q4 (≥39.88 µg/m³).

An IQR value was set at 7.8 µg/m³.

All of the quartiles’ PM_2.5 concentrations exceeded the WHO air quality guidelines.

Adult Taiwanese participants between the age of 20 – 90 years with a mean (IQR) age of 67.8 (57.5 to 76.6) years and diagnosed with CKD (n = 6,628).

Study period: 2003 – 2015

 A positive relationship between PM_2.5 exposure and risk for kidney failure requiring replacement therapy was demonstrated for PM_2.5 increments of 10 µg/m³ and IQR of 7.8 µg/m³. Furthermore, increased risk of progression to kidney failure requiring replacement therapy was shown across increasing PM_2.5 quartiles.

A significant increasing linear trend in risk for progression to kidney failure across the increasing PM_2.5 exposure levels was shown (p < 0.001).

Feng Y. et al. (2021a) [55]

(cohort study)

The median PM_2.5 concentration level amounted to 9.17 µg/m³ (range: 0.70 to 23.62 µg/m³).

The levels exceeded the air quality guidelines set by the WHO.

Older kidney failure patients (USA) aged ≥65 years (median age = 74, IQR: 69 to 80 years) at dialysis initiation, who started their first dialysis between 2010 and 2016 (n = 384,276) with a median follow-up of 1.84 years (IQR: 0.77 to 3.25 years).

Study period: Jan. 2010 – Dec. 2016

No association could be observed between PM_2.5 <12 µg/m³ and mortality risk; however, when PM_2.5 concentrations were >12 µg/m³, associations could be observed with each 10 µg/m³ PM_2.5 increase in mortality risk among older dialysis patients (p < 0.05).

The association appeared nonlinear; the dose-response association changed when the PM_2.5 levels reached ~12 µg/m³.

Furthermore, when diabetes was the primary cause of kidney failure, a higher PM_2.5-associated mortality risk was observed (p < 0.05).

Pierotti et al. (2018) [56]

(retrospective cohort study)

The average median (IQR) PM_2.5 exposure level was 10.0 (1.4) µg/m³.

The average PM_2.5 concentration exceeded the new WHO air quality guidelines.

Patients who received a kidney transplant between 2000 and 2008 in Great Britain (n = 11,607) with a mean ± SD age of 43.6 ± 15.9 years at transplantation.

Study period: Jan. 2000 – Dec. 2008

Exposure to PM_2.5 was associated with renal transplant failure in univariate analyses, but not after adjustment for confounders.

An increased risk of kidney graft failure was shown for each 5 µg/m³ increase in PM_2.5 (p = 0.03).

Chang et al. (2021) [57] (retrospective cohort study)

The median (IQR) PM_2.5 level the year before kidney transplantation was 9.8 (8.3 to 11.9) µg/m³.

Exposure was divided into 4 quartiles: Q1 (1.2 – <8.3 µg/m³), Q2 (8.3 - <9.8 µg/m³), Q3 (9.8 - <11.9 µg/m³), and Q4 (11.9 - <22.4 µg/m³).

The median PM_2.5 concentration exceeded the newly set air quality guidelines by the WHO.

Patients (USA) receiving a kidney transplant between 2004 and 2016 (n = 112,098) with 62.91% being over 50 years old.

Study period: 2004 - 2021

An increased PM_2.5 level, compared to quartile 1, was not associated with higher odds of acute kidney rejection for quartile 2, but was associated with increased odds for quartile 3 (p < 0.001).

Increased PM_2.5 levels were also associated with an increased risk of death-censored graft failure and all-cause death (p < 0.001)

Dehom et al. (2021) [58]

(retrospective cohort study)

The PM_2.5 concentration levels were divided into 3 tertiles: T1 (2.1 – 9.3 µg/m³), T2 (>9.3 µg/m³ - 11.0 µg/m³), and T3 (>11.0 – 18.4 µg/m³).

The medians of all tertiles (T1: 7.9 µg/m³, T2: 10.3 µg/m³, and T3: 11.9 µg/m³) exceeded the air quality guidelines set by the WHO.

Adults (≥18 years; USA) who received a kidney transplant between 2001 and 2015 (n = 93,857) with a median follow-up of 14.91 years.

Study period: 2001 – 2015

 A 10 µg/m³ increase in PM_2.5 concentrations was associated with in increased risk of all-cause mortality in kidney transplant recipients (p < 0.05). Black recipients had higher risks of all-cause death than non-blacks. High levels of PM_2.5 were also associated with all-cause mortality (p < 0.05).

Feng Y. et al. (2021b) [59]

(retrospective cohort study)

The median PM_2.5 level at the time of transplant was 9.2 µg/m³ with a range of 0.7 to 29.7 µg/m³.

The median exceeded the new air quality guidelines of the WHO.

Adult kidney transplant recipients (USA) receiving a first transplant between January 1st, 2010, and December 30th, 2016 (n = 87,223) with a median follow-up of 5.3 years.

To analyze the results regarding one-year acute rejection, the sample population was restricted to n = 83,669 due to missing follow-up data.

Study period: Jan. 2010 – Dec. 2016

 A 10 µg/m³ increase in PM_2.5 concentration was associated with an increased risk of delayed graft function, one-year acute rejection, and all-cause mortality (p < 0.05).

When only analyzing the population exposed to PM_2.5 levels ≤12 µg/m³, no association could be shown with one-year acute rejection.

Additionally, no association between an increase of 10 µg/m³ in PM_2.5 levels and death-censored graft loss.