Table 1. Baseline characteristics of nine randomized controlled trials in this meta-analysis.
| First author | Year | Country | Cancer | Trial | Population characteristics | 25(OH)D level at baseline and follow-up | Eligibility criteria on supplement use | Trial duration (months) | Contrast | Vit D3 dose | Ca dose |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Daksha P. Trivedi | 2003 | U.K. | All cancer | NA | General population aged 65–85 years | Intervention: NA to 74.4 nmol/l at 4 years; control: NA to 53.4 nmol/l at 4 years | Exclude Vit D supplement users | 70 | Vit D3 vs placebo | 100000 IU per 4 months over 5 years | NA |
| Jean Wactawski-Wende | 2006 | U.S.A. | Colorectal cancer | NCT00000611 | Postmenopausal women aged 50–79 years | NA | Allow for non-protocol supplement of Vit D up to 600IU per day; of Ca up to 1000 mg per day | 84 | Vit D3 plus Ca vs placebo | 400 IU per day for 7 years | 1000 mg per day for 7 years |
| Joan M. Lappe | 2007 | U.S.A. | All cancer except skin cancer | NCT00352170 | Healthy postmenopausal women aged >55 years | Intervention: 71.8–96 nmol/l at 1 year; control: 72.1 to 71.1 nmol/l at 1 year | Not specified | 48 | Vit D3 plus Ca vs placebo | 1100 IU per day | 1500 mg per day |
| Alison Avenell | 2012 | U.K. | All cancer | RECORD Trial | 70 years and older with previous low-trauma fracture | Intervention: 38-62 nmol/l at 1 year; control: 38 to NA nmol/l | Allow for non-protocol supplement of Vit D up to 200IU per day; of Ca up to 500 mg per day | 98 | Vit D3 (w/t, w/o Ca) vs no Vit D3 (w/t, w/o Ca) | 800 IU per day for 24-62 months | 1000 mg per day |
| John A. Baron | 2015 | U.S.A. | Colorectal adenomas | NA | Age 45–75 years with at least one colorectal adenoma removed within 120 days before enrollment and had no remaining polyps after a complete colonoscopy | NA | Allow for non-protocol supplement of Vit D up to 1000IU per day; of Ca up to 400 mg per day; Excluded patients with 25(OH)D level lower than 12 ng/ml or higher than 90 ng/ml | 113 | Vit D3 plus Ca vs placebo | 1000 IU per day | 1200 mg per day |
| Hans-Christian Pommergaard | 2015 | Europe, Russia, U.S.A. | Colorectal adenomas | NCT00486512 | Patients with one or more sporadic adenomas removed from the colon or rectum within the last 3 months | NA | Exclude Vit D supplement users | 72 | Calcitriol vs placebo | 0.5 μg per day for 3 years | NA |
| Joan M. Lappe | 2017 | U.S.A. | All cancer except nonmelanoma skin cancer | NA (NCT01052051) | Postmenopausal women aged ≥55 years | Intervention: 33.0-42.5 ng/ml; control: 32.7–30.9 ng/ml | Allow for non-protocol supplement of Vit D up to 800IU per day; of Ca up to 1500 mg per day | 48 | Vit D3 plus Ca vs placebo | 2000 IU per day | 1500 mg per day |
| Tadashi Akiba | 2018 | Japan | stage IA-IIIA NSCLC | UMIN | Age: 20–75 years | Intervention: 21-39 ng/mL; control: 22-24 ng/mL | Exclude Vit D supplement users | 96 | Vit D3 vs placebo | 1200 IU per day for 12 months | NA |
| Robert Scragg | 2018 | U.S.A. | All cancer except nonmelanoma skin cancer | ViDA study | Age: 50–84 years | Intervention: NA to 25.5 ng/ml; control: NA to 25.2 ng/ml | Exclude Vit D supplement users | 57 | Vit D3 vs placebo | initial bolus dose of 200000 IU and followed by monthly doses of 100000 IU for a median of 3.3 years (2.5–4.2 years) | NA+A1:N10 |
| JoAnn E. Manson | 2018 | U.S.A. | All cancer | NCT01169259 | General population with men aged 50 years or older and women aged 55 years or older | Intervention: 74–104 nmol/l at 1 year/ control: NA | Allowed for non-protocol supplement of Vit D up to 800IU per day | 73 | Vit D3 vs placebo | 2000 IU per day for 5 years | NA |
Abbreviations: Ca, calcium; NA, not available; NSCLC, non-small-cell lung cancer; Vit D, vitamin D; w/t, with; w/o, without.