Table 1 Characteristics of participants in the Korea Nurses’ Health Study according to menstrual cycle regularity and length
From: Factors associated with regularity and length of menstrual cycle: Korea Nurses’ Health Study
Characteristicsa | All (n = 9335) | Menstrual cycle regularity | p valueb | Menstrual cycle lengthc | p valueb | |||
|---|---|---|---|---|---|---|---|---|
Regular | Irregular | < 26 days | 26–31 days | 32–50 days | ||||
Number | 7359 (78.83) | 1976 (21.17) | 886 (9.80) | 5794 (64.07) | 2363 (26.13) | |||
Age, years | 30.83 ± 5.64 | 31.24 ± 5.71 | 29.31 ± 5.12 | < 0.001 | 31.39 ± 6.34 | 31.33 ± 5.79 | 29.61 ± 4.76 | < 0.001 |
Menarche age, years | ||||||||
≤ 12 | 2139 (22.91) | 1709 (23.22) | 430 (21.76) | < 0.001 | 205 (23.14) | 1326 (22.88) | 532 (22.52) | 0.435 |
13 | 2544 (27.25) | 2033 (27.63) | 511 (25.86) | 249 (28.10) | 1599 (27.60) | 631 (26.70) | ||
14 | 2157 (23.11) | 1731 (23.52) | 426 (21.56) | 181 (20.43) | 1357 (23.42) | 556 (23.53) | ||
≥ 15 | 2495 (26.73) | 1886 (25.63) | 609 (30.82) | 251 (28.33) | 1512 (26.10) | 644 (27.25) | ||
Parity | ||||||||
Nulliparous | 6620 (70.97) | 5019 (68.25) | 1601 (81.10) | < 0.001 | 617 (69.72) | 3942 (68.08) | 1816 (76.92) | < 0.001 |
1 | 1023 (10.97) | 860 (11.69) | 163 (8.26) | 100 (11.30) | 675 (11.66) | 222 (9.40) | ||
2+ | 1685 (18.06) | 1475 (20.06) | 210 (10.64) | 168 (18.98) | 1173 (20.26) | 323 (13.68) | ||
Body mass index, kg/m2 | 20.86 ± 2.68 | 20.86 ± 2.64 | 20.85 ± 2.82 | 0.599 | 20.62 ± 2.47 | 20.88 ± 2.62 | 20.80 ± 2.78 | 0.011 |
Vigorous physical activity, METs-hours/week | 7.59 ± 21.16 | 7.59 ± 21.57 | 7.58 ± 19.56 | 0.611 | 7.25 ± 17.83 | 7.57 ± 22.00 | 7.65 ± 20.62 | 0.775 |
Cigarette smoking | ||||||||
Never | 9073 (97.21) | 7160 (97.31) | 1913 (96.86) | 0.282 | 857 (96.73) | 5642 (97.39) | 2292 (97.04) | 0.419 |
Ever | 260 (2.79) | 198 (2.69) | 62 (3.14) | 29 (3.27) | 151 (2.61) | 70 (2.96) | ||
Alcohol drinking, g/day | ||||||||
None | 3087 (34.65) | 2450 (34.86) | 637 (33.86) | 0.017 | 271 (31.84) | 1930 (34.92) | 798 (35.34) | 0.240 |
< 5 | 3448 (38.70) | 2757 (39.23) | 691 (36.74) | 339 (39.84) | 2172 (39.30) | 849 (37.60) | ||
5– < 15 | 1295 (14.54) | 1001 (14.24) | 294 (15.63) | 124 (14.57) | 779 (14.09) | 345 (15.28) | ||
≥ 15 | 1079 (12.11) | 820 (11.67) | 259 (13.77) | 117 (13.75) | 646 (11.69) | 266 (11.78) | ||
Coffee consumption, cups/day | 0.94 ± 1.24 | 0.94 ± 1.23 | 0.91 ± 1.27 | 0.007 | 0.97 ± 1.29 | 0.98 ± 1.26 | 0.84 ± 1.18 | < 0.001 |
Rotating night shift, nights/month | ||||||||
None | 2734 (29.32) | 2259 (30.73) | 475 (24.09) | < 0.001 | 288 (32.58) | 1788 (30.90) | 597 (25.29) | < 0.001 |
< 7 | 3409 (36.57) | 2673 (36.36) | 736 (37.32) | 309 (34.95) | 2087 (36.06) | 910 (38.54) | ||
≥ 7 | 3180 (34.11) | 2419 (32.91) | 761 (38.59) | 287 (32.47) | 1912 (33.04) | 854 (36.17) | ||
On feet at work, hours/day | ||||||||
≤ 4 | 2989 (32.02) | 2442 (33.18) | 547 (27.68) | < 0.001 | 281 (31.72) | 1905 (32.88) | 719 (30.43) | 0.004 |
5–8 | 4254 (45.57) | 3368 (45.77) | 886 (44.84) | 381 (43.00) | 2671 (46.10) | 1080 (45.70) | ||
≥ 9 | 2092 (22.41) | 1549 (21.05) | 543 (27.48) | 224 (25.28) | 1218 (21.02) | 564 (23.87) | ||
Heavy lifting at work, times/day | ||||||||
0 | 1590 (17.03) | 1303 (17.70) | 287 (14.53) | < 0.001 | 153 (17.27) | 1034 (17.85) | 356 (15.07) | 0.038 |
1–5 | 5472 (58.62) | 4329 (58.83) | 1143 (57.84) | 509 (57.45) | 3390 (58.51) | 1426 (60.35) | ||
≥ 6 | 2273 (24.35) | 1727 (23.47) | 546 (27.63) | 224 (25.28) | 1370 (23.64) | 581 (24.58) | ||