Table 1.
Baseline characteristics of participants according to vitamin D supplementationa
| Variable | Placebo group (n=12,944) | Vitamin D group (n=12,927) | P value |
|---|---|---|---|
| Age, year | 67.1 (7.1) | 67.1 (7.1) | 0.84 |
| Women, % | 6538 (51) | 6547 (51) | 0.83 |
| Race/ethnicity, % | 0.97 | ||
| Non-Hispanic white | 9033 (71) | 9013 (71) | |
| African American | 2553 (20) | 2553 (20) | |
| Others | 1071 (9) | 1081 (9) | |
| Family history of colorectal cancer, % | 1574 (13) | 1609 (14) | 0.51 |
| Colonoscopy or sigmoidoscopy in the past 10 years, % | 9654(75) | 9671(75) | 0.67 |
| Colonoscopy in the past 10 years, % | 9467 (73) | 9448 (73) | 0.93 |
| Sigmoidoscopy in the past 10 years, % | 1659 (14) | 1540 (13) | 0.04 |
| History of colorectal polyps, % | 3211 (25) | 3224 (25) | 0.80 |
| Smoking status, % | 0.88 | ||
| Never | 6620 (52) | 6565 (52) | |
| Past | 5221 (41) | 5243 (41) | |
| Current | 915 (7) | 921 (7) | |
| Body mass index, kg/m2 | 28.1 (5.8) | 28.1 (5.7) | 0.50 |
| Physical activity, MET-hours/week | 22.9 (25.9) | 22.5 (25.8) | 0.15 |
| Use of aspirin, % | 5814 (46) | 5756 (45) | 0.53 |
| Use of vitamin D supplements, %b | 5533 (43) | 5497 (43) | 0.72 |
| Use of calcium supplements, % | 2539 (20) | 2627 (20) | 0.16 |
| Use of multivitamin supplements, % | 5656 (44) | 5750 (45) | 0.20 |
| Alcohol use, % | 0.31 | ||
| Never | 4017 (32) | 3977 (31) | |
| Rarely to less than once per week | 968 (8) | 941 (7) | |
| 1–6/week | 4385 (34) | 4511 (36) | |
| Daily | 3364 (26) | 3274 (26) | |
| Serum 25(OH)D, ng/mLc | 30.8 (10.0) | 30.9 (10.0) | 0.35 |
Abbreviations: DHA, docosahexaenoic acid; EPA, eicosapentaenoic acid; MET, metabolic equivalent.
a
Mean (standard deviation) and percentage are presented for continuous and categorical variables, respectively.
b
To be eligible for the trial, participants are required to limit consumption of supplemental vitamin D to no more than 800 IU/day from all supplemental sources combined.
c
Serum data were available in 7,891 participants in the control group (61%) and 7,896 in the intervention group (61%) who provided a blood sample at enrollment.