Table 1. Mean plasma analyte levels and baseline characteristics for cases and controls Health Professionals Follow-up Study (HPFS), 1994–2002 and Nurses' Health Study (NHS), 1990–2008 (combined).
| Characteristics | Cases(N = 499) | Controls (N = 992) | p-value ‡‡‡‡ |
| Plasma 25(OH)D (ng/mL) | 26.2 (10.3) | 27.6 (9.8) | <0.001 |
| Plasma IGF-1 (ng/mL) | 185 (69.7) | 175 (66.3) | 0.02 |
| Plasma IGF-BP3 (ng/mL) | 4352 (1025) | 4291 (1013) | 0.22 |
| Molar ratio IGF-1/IGF-BP3 | 0.15 (0.05) | 0.15 (0.05) | 0.03 |
| Plasma C-Peptide (ng/mL) (excluding participants with history of diabetes) | 2.4 (1.6) | 2.3 (1.9) | 0.52 |
| Sex ‡‡‡‡‡ | |||
| Male | 174 (34.9) | 346 (34.9) | |
| Female | 325 (65.1) | 646 (65.1) | 1.00 |
| Age at blood donation, years ‡‡‡‡‡ | 61.7 (8) | 61.6 (7.9) | 0.95 |
| Hours since last meal ‡‡‡‡‡ | |||
| <8 hours | 129 (25.9) | 248 (25.0) | |
| ≥ 8 hours | 335 (67.1) | 671 (67.6) | |
| Missing | 35 (7.1) | 73 (7.4) | 0.92 |
| Season of blood donation‡‡, ‡‡‡‡‡ | |||
| Winter | 179 (35.9) | 361 (36.4) | |
| Summer | 111 (22.2) | 213 (21.5) | |
| Spring/Fall | 209 (41.9) | 418 (42.1) | 0.94 |
| Body mass index (BMI), kg/m2 $ | 26.0 (4.5) | 25.5 (4.1) | 0.08 |
| Physical activity, MET- hour/wk$ | 22.6 (26.1) | 23.3 (26.9) | 0.93 |
| Aspirin use $ | |||
| <2 tablets/week | 206 (41.3) | 325 (32.8) | |
| ≥2 tablets/week | 139 (27.9) | 318 (32.1) | |
| Past user | 154 (30.9) | 349 (35.2) | 0.005 |
| Pack-years of smoking ‡ | 26.2 (22) | 24 (19.6) | 0.22 |
| Family history of colorectal cancer | |||
| No | 410 (82.2) | 865 (87.2) | |
| Yes | 89 (17.8) | 127 (12.8) | 0.009 |
| Alcohol, g/d † | 8.7 (11.7) | 8.4 (11.6) | 0.77 |
| Methionine g/d † | 1.90 (0.35) | 1.90 (0.34) | |
| Total folate intake, µg/d † | 424 (187) | 456 (212) | 0.09 |
| Total vitamin D intake , IU/d ‡‡‡ | 375 (265) | 400 (281) | 0.14 |
| Vitamin D from supplements only , IU/d ‡‡‡ | 145 (229) | 159 (229) | 0.23 |
| Total calcium intake, mg/d ‡‡‡ | 908 (340) | 953 (357) | 0.008 |
| Total retinol intake, IU/d ‡‡‡ | 3886 (4466) | 4241 (4462) | 0.02 |
| Total fiber intake, g/d † | 18.6 (5.6) | 19.2 (6.0) | 0.12 |
| Processed meat intake, serv/d † | 0.32 (0.35) | 0.29 (0.30) | 0.11 |
| Unprocessed red meat intake, serv/d † | 0.59 (0.33) | 0.57 (0.32) | 0.18 |
| Unprocessed red and processed meat, serv/d † | 0.92 (0.57) | 0.86 (0.52) | 0.07 |
| Total milk intake, serv/d ‡‡‡ | 0.98 (1.05) | 1.0 (0.99) | 0.34 |
*Numbers in parenthesis indicate standard deviation for means and percentages for frequencies.
$If not noted otherwise (see below) information obtained from 1994 questionnaires (HPFS) or 1990 questionnaire (NHS),
if missing carried forward from most recent questionnaire prior to 1994 (HPFS) or prior to 1990 (NHS).
For dietary intake: cumulative average intake 1986-1994 (HPFS) and 1980-1990 (NHS), up to 9 participants have missing information.
Never smokers (N = 633) and participants with missing values (N = 16) were excluded when calculating means.
Season defined as: winter: November, December, January, February, March, summer: June, July, August, September, spring/fall : all other months.
Intake calculated from FFQ in 1994 (HPFS) and FFQ in 1990 (NHS), if missing carried forward from most recent questionnaire prior to 1994 (HPFS) or prior to 1990 (NHS) up to 9 participants have missing information.
P-values calculated using Wilcoxon signed rank test for plasma biomarkers, Wilcoxon rank sum test for other continuous variables, and χ2 tests for categorical variables.
Matching factor