Table 1.
Baseline characteristics (1998) of the study sample (n = 2254) in the Norwegian Offshore Petroleum Workers cohort.
| Variables | Cases (n = 189) | Non-cases (n = 2065) | ||
|---|---|---|---|---|
| Age (years), median (range) | 54 | (31–76) | 54 | (20–80) |
| 10-year birth cohort, n (%) | ||||
| 1915–1924 | 2 | (1.1) | 23 | (1.1) |
| 1925–1934 | 27 | (14.3) | 320 | (15.5) |
| 1935–1944 | 67 | (35.5) | 750 | (36.3) |
| 1945–1954 | 64 | (33.9) | 690 | (33.4) |
| 1955–1964 | 25 | (13.2) | 236 | (11.4) |
| 1965–1979 | 4 | (2.1) | 46 | (2.2) |
| Education, n (%) | ||||
| Compulsory | 29 | (15.3) | 327 | (15.8) |
| Vocational | 93 | (49.2) | 1056 | (51.1) |
| Upper secondary | 31 | (16.4) | 281 | (13.6) |
| University/college | 32 | (16.9) | 384 | (18.6) |
| Missing | 4 | (2.1) | 17 | (0.8) |
| BMI (kg/m2), n (%) | ||||
| 12–18.4 | 1 | (0.5) | 6 | (0.3) |
| 18.5–24.9 | 74 | (39.2) | 838 | (40.6) |
| 25.0–29.9 | 97 | (51.3) | 1012 | (49.0) |
| ≥30.0 | 13 | (6.9) | 177 | (8.6) |
| Missing | 4 | (2.1) | 32 | (1.6) |
| Physical activity, n (%) | ||||
| Never | 55 | (29.1) | 508 | (24.6) |
| 1–3 times/month | 49 | (25.9) | 589 | (28.5) |
| 1–2 times/week | 46 | (24.3) | 501 | (24.3) |
| 3–4 times/week | 30 | (15.9) | 279 | (13.5) |
| 5–7 times/week | 6 | (3.2) | 144 | (7.0) |
| Missing | 3 | (1.6) | 44 | (2.1) |
| Tobacco smoking, n (%)a | ||||
| Never | 14 | (7.4) | 449 | (21.7) |
| Former | 76 | (40.2) | 844 | (40.9) |
| Current <12 cigarettes per day | 43 | (22.8) | 353 | (17.1) |
| Current ≥12 cigarettes per day | 48 | (25.4) | 348 | (16.9) |
| Missing | 8 | (4.3) | 71 | (3.4) |
| Work-history | ||||
| Year of first employment, median (range) | 1978 | (1965–1998) | 1979 | (1965–1998) |
| Year of first employment, n (%) | ||||
| 1965–1974 | 33 | (17.5) | 294 | (14.2) |
| 1975–1984 | 103 | (54.5) | 1226 | (59.4) |
| 1985–1998 | 53 | (28.0) | 545 | (26.4) |
| Total employment duration in years, median (range) | 10.5 | (0.3–33.0) | 12.4 | (0.1–33.5) |
| Total employment duration in years by quartiles, n (%) | ||||
| >0–<6.0 | 50 | (26.5) | 522 | (25.3) |
| 6.0–<12.2 | 54 | (28.6) | 502 | (24.3) |
| 12.2–<18.3 | 28 | (14.8) | 535 | (25.9) |
| 18.3–33.5 | 57 | (30.2) | 506 | (24.5) |
| Benzene exposure | ||||
| Duration of benzene exposure (years), median (range) | 5.1 | (0–26.0) | 4.2 | (0–33.5) |
| Duration of benzene exposure (years), n (%)b | ||||
| 0 | 49 | (25.9) | 631 | (30.6) |
| >0–<5.5 | 46 | (24.3) | 481 | (23.3) |
| 5.5–<13.3 | 38 | (20.1) | 485 | (23.5) |
| 13.3–<18.8 | 23 | (12.2) | 239 | (11.6) |
| 18.8–33.5 | 33 | (17.5) | 229 | (11.1) |
| Cumulative benzene exposure, median (range) | 6.3 | (0–43.0) | 5.2 | (0–51.4) |
| Cumulative benzene exposure, n (%)b, c | ||||
| 0 | 49 | (25.9) | 631 | (30.6) |
| >0–<2.0 | 47 | (24.9) | 479 | (23.2) |
| 2.0–<7.6 | 38 | (20.1) | 486 | (23.5) |
| 7.6–<15.3 | 27 | (14.3) | 235 | (11.4) |
| 15.3–51.4 | 28 | (14.8) | 234 | (11.3) |
| Avg. intensity of benzene exposure, median (range)d | 0.5 | (0–1.9) | 0.5 | (0–1.9) |
| Avg. intensity of benzene exposure, n (%)d | ||||
| 0 | 49 | (25.9) | 631 | (30.6) |
| >0–0.5 | 78 | (41.3) | 823 | (39.9) |
| >0.5–1.0 | 30 | (15.9) | 313 | (15.2) |
| >1 | 32 | (16.3) | 298 | (14.4) |
| Crude oil skin exposure | ||||
| Duration (years), n (%)e | ||||
| 0 | 46 | (24.3) | 493 | (23.9) |
| >0–<6.7 | 48 | (25.4) | 526 | (25.5) |
| 6.7–<14.9 | 45 | (23.8) | 525 | (25.4) |
| 14.9–33.5 | 50 | (26.5) | 521 | (25.2) |
| Cumulative exposure, n (%)c, e | ||||
| 0 | 46 | (24.3) | 493 | (23.9) |
| >0–<7.5 | 42 | (22.2) | 532 | (25.8) |
| 7.5–<18.0 | 47 | (24.9) | 523 | (25.3) |
| 18.0–70.5 | 54 | (28.6) | 517 | (25.0) |
| Mineral oil skin exposure | ||||
| Duration (years), n (%)e | ||||
| 0 | 75 | (39.7) | 809 | (39.2) |
| >0–<6.0 | 39 | (20.6) | 424 | (20.5) |
| 6.0–<13.5 | 31 | (16.4) | 423 | (20.5) |
| 13.5–30.7 | 44 | (23.3) | 409 | (19.8) |
| Cumulative exposure, n (%)c, e | ||||
| 0 | 75 | (39.7) | 809 | (39.2) |
| >0–<6.7 | 34 | (18.0) | 423 | (20.5) |
| 6.7–<19.6 | 40 | (21.2) | 417 | (20.2) |
| 19.6–60.0 | 40 | (21.2) | 416 | (20.2) |
| Mineral oil inhalation exposure | ||||
| Duration (years), n (%)e | ||||
| 0 | 56 | (29.6) | 590 | (28.6) |
| >0–<6.1 | 48 | (25.4) | 488 | (23.6) |
| 6.1–<14.0 | 37 | (19.6) | 500 | (24.2) |
| 14.0–32.0 | 48 | (25.4) | 487 | (23.6) |
| Cumulative exposure, n (%)c, e | ||||
| 0 | 56 | (29.6) | 590 | (28.6) |
| >0–<6.8 | 44 | (23.3) | 492 | (23.8) |
| 6.8–<18.1 | 41 | (21.7) | 496 | (24.0) |
| 18.1–60.0 | 48 | (25.4) | 487 | (23.6) |
| Diesel exhaust exposure | ||||
| Duration (years), n (%)e | ||||
| 0 | 102 | (54.0) | 1087 | (52.6) |
| >0–<4.0 | 30 | (15.9) | 325 | (15.7) |
| 4.0–<11.0 | 28 | (14.8) | 327 | (15.8) |
| 11.0–30.7 | 29 | (15.3) | 326 | (15.8) |
| Cumulative exposure, n (%)c, e | ||||
| 0 | 102 | (54.0) | 1087 | (52.6) |
| >0–<2.4 | 30 | (15.9) | 326 | (15.8) |
| 2.4–<7.5 | 25 | (13.2) | 329 | (15.9) |
| 7.5–61.2 | 32 | (16.9) | 323 | (15.6) |
| PAH exposure (proxy) | ||||
| Never | 107 | (56.6) | 1226 | (59.4) |
| Ever | 82 | (43.4) | 839 | (40.6) |
| Work as a painter | ||||
| Never | 145 | (76.7) | 1606 | (77.8) |
| Ever | 44 | (23.3) | 459 | (22.2) |
aTobacco-smoking status as current smoker below or above the median average intensity.
bCategorised into unexposed (0) and tertiles among exposed. To capture the tail of the distribution, the upper tertile was divided into two by its median.
cCumulative exposure: JEM-rating multiplied by duration (in years) for each employment period and summarised for each individual from the start of employment until 31 December 1998.
dAverage intensity: defined as the cumulative exposure divided by the total duration of exposure (in years) and investigated as a categorical variable with an unexposed group and three exposed categories.
eCategorised into non-exposed (0) and tertiles among exposed.