Table 1. Demographic and clinical characteristics of new users of H2 blockers who were or were not exposed to NDMA

Characteristic Full unmatched cohort(n = 95,656) SMD* Propensity score-matched cohort(n = 55,584) SMD*
No exposure NDMA exposure No exposure NDMA exposure
Total, n (%) 65,321 (68.3) 30,335 (31.7) 27,792 (50.5) 27,792 (50.5)
Median [IQR] years of follow-up 5.2 [2.2 to 8.0] 6.8 [3.9 to 9.3] 0.376 6.6 [4.0 to 8.7] 6.8 [3.9 to 9.2] 0.010
Age, years, mean (SD) 51.6 (12.8) 54.7 (11.9) 0.247 54.3 (11.8) 54.4 (12.1) 0.008
Sex, male, n (%) 22,529 (34.5) 12,019 (39.6) 0.106 10,644 (38.3) 10,642 (38.3) <0.001
Region of residence, n (%)
Rural 36,747 (56.3) 28,574 (59.1) 0.057 16,520 (59.4) 16,517 (59.4) <0.001
Urban 28,574 (43.7) 12,409 (40.9) 0.057 11,272 (40.6) 11,275 (40.6) <0.001
Body mass index, kg/m2, n (%)
 <25 42,570 (65.2) 18,755 (61.8) 0.071 17,646 (63.5) 17,481 (62.9) 0.012
 25–30 20,208 (30.9) 10,113 (33.3) 0.051 9,090 (32.7) 9,143 (32.9) 0.004
 ≥30 2,543 (3.9) 1,467 (4.8) 0.044 1,056 (3.8) 1,168 (4.2) 0.020
Systolic blood pressure, mmHg, mean (SD) 126.2 (17.8) 125.7 (17.6) 0.028 126.0 (17.8) 125.9 (17.7) 0.006
Diastolic blood pressure, mmHg, mean (SD) 78.8 (11.2) 77.9 (11.2) 0.080 78.2 (11.2) 78.0 (11.1) 0.018
Fasting blood glucose, mg/dL, mean (SD) 101.1 (35.7) 98.8 (30.9) 0.069 99.7 (32.3) 99.1 (30.7) 0.018
Serum total cholesterol, mg/dL, mean (SD) 200.1 (40.7) 198.8 (38.8) 0.033 199.5 (40.3) 199.0 (38.9) 0.013
History of diabetes mellitus, n (%) 4,256 (6.5) 2,962 (9.8) 0.121 1,814 (6.5) 1,816 (6.5) <0.001
History of stroke, n (%) 532 (0.8) 364 (1.2) 0.141 109 (0.4) 109 (0.4) <0.001
History of hypertension, n (%) 10,566 (16.2) 6,711 (22.1) 0.150 5,474 (19.7) 5,478 (19.7) <0.001
Charlson comorbidity index, n (%)
 0-1 46,329 (70.9) 19,625 (64.7) 0.133 19,010 (68.4) 18,873 (67.9) 0.011
 2 10,759 (16.5) 6,027 (19.9) 0.088 5,280 (19.0) 5,362 (19.3) 0.008
 ≥3 8,233 (12.6) 4,683 (15.4) 0.084 3,502 (12.6) 3,557 (12.8) 0.006
Household income, n (%) 27,792
 Low (0–39 percentile) 21,576 (33.0) 10,431 (34.4) 0.030 9,139 (32.9) 9,173 (33.0) 0.002
 Middle (40–79 percentile) 19,960 (30.6) 9,082 (29.9) 0.015 8,619 (31.0) 8,647 (31.1) 0.002
 High (80–100 percentile) 23,785 (36.4) 10,822 (35.7) 0.015 10,034 (36.1) 9,972 (35.9) 0.004
Smoking, n (%)
 Never smoker 50,045 (76.6) 22,076 (72.8) 0.087 20,732 (74.6) 20,728 (74.6) <0.001
 Ex-smoker 4,714 (7.2) 2,433 (8.0) 0.030 1,958 (7.0) 1,957 (7.0) <0.001
 Current smoker 10,562 (16.2) 5,826 (19.2) 0.079 5,110 (18.4) 5,107 (18.4) <0.001
Alcoholic drinks, days per week, n (%)
 <1 51,023 (78.1) 23,629 (77.9) 0.007 21,677 (78.0) 21,680 (78.0) <0.001
 1–2 8,702 (13.3) 3,711 (12.2) 0.033 3,530 (12.7) 3,471 (12.5) 0.006
 3–4 3,351 (5.1) 1,744 (5.7) 0.027 1,501 (5.4) 1,529 (5.5) 0.004
 ≥5 2,245 (3.4) 1,251 (4.1) 0.037 1,084 (3.9) 1,112 (4.0) 0.005
Physical activity sessions per week, n (%)
 0 37,042 (56.7) 17,509 (57.7) 0.020 15,935 (57.3) 15,984 (57.5) 0.004
 1–2 12,331 (18.9) 5,462 (18.0) 0.023 5,109 (18.4) 5,058 (18.2) 0.005
 3–4 6,912 (10.6) 2,998 (9.9) 0.023 2,802 (10.1) 2,779 (10.0) 0.003
 5–6 3,224 (4.9) 1,427 (4.7) 0.009 1,334 (4.8) 1,330 (4.8) <0.001
 7 5,812 (8.9) 2,939 (9.7) 0.028 2,612 (9.4) 2,641 (9.5) 0.003
Use of medications, n (%)
 Proton pump inhibitors 3,647 (5.6) 2,239 (7.4) 0.073 1,587 (5.7) 1,644 (5.9) 0.009
 Statins 3,249 (5.0) 2,347 (7.7) 0.011 1,433 (5.2) 1,437 (5.2) <0.001
 Systemic glucocorticoids 27,518 (42.1) 11,945 (39.4) 0.067 10,908 (39.2) 10,889 (39.2) <0.001
 Metformin 2,261 (3.5) 1,701 (5.6) 0.101 889 (3.2) 882 (3.2) <0.001
 Aspirin 3,754 (5.7) 2,307 (7.6) 0.076 1,476 (5.3) 1,471 (5.3) <0.001
 Hormone replacement therapy 4,830 (7.4) 2,362 (7.8) 0.015 2,039 (7.3) 2,042 (7.3) <0.001
Abbreviations here: H2 blocker, histamine H2 receptor antagonist; NDMA, N-nitrosodimethylamine; IQR, interquartile range; SD, standard deviation; SMD, standardized mean difference.
A standardized mean difference (SMD) below 0.1 indicates no major imbalance. All SMD values were less than 0.02 in the propensity score-matched cohort.