Baseline characteristics by treatment
| Total participants | 800 IU vitamin D3 | 2000 IU vitamin D3 | Difference(p values) | |
| Participants, n (%) | 273 (100) | 136 (49.8) | 137 (50.2) | |
| Women, n (%) | 146 (53.5) | 77 (56.6) | 69 (50.4) | 0.30 |
| Age (years) | 70.3 (6.4) | 70.5 (6.0) | 70.2 (6.8) | 0.67 |
| Patients ≥70 years, n (%) | 130 (47.6) | 70 (51.5) | 60 (43.8) | 0.20 |
| Low preoperative WOMAC function score, n (%)* | 50 (18.3) | 25 (18.4) | 25 (18.3) | 0.98 |
| Osteoarthritis also on the other knee, n (%) | 223 (81.7) | 112 (82.4) | 111 (81.0) | 0.78 |
| Height (cm) | 168.4 (9.2) | 167.7 (9.1) | 169.2 (9.3) | 0.17 |
| Weight (kg) | 77.5 (14) | 75.4 (14.3) | 79.5 (13.4) | 0.02 |
| Body mass index (kg/m2) | 27.2 (3.9) | 26.7 (4.1) | 27.7 (3.8) | 0.04 |
| Charlson Comorbidity Index (score 0–37) | 0.5 (0.9) | 0.5 (1) | 0.5 (0.8) | 0.82 |
| Mini-Mental State Examination (score 0–30) | 28.0 (1.5) | 28.1 (1.2) | 27.8 (1.6) | 0.21 |
| Baseline 25-hydroxyvitamin D (ng/mL) | 27.3 (12.4) | 27.2 (12.7) | 27.3 (12.2) | 0.96 |
| <10, n (%) | 17 (6.3) | 8 (6.0) | 9 (6.6) | 0.84 |
| <20, n (%) | 85 (31.4) | 44 (32.8) | 41 (29.9) | 0.61 |
| WOMAC scores (score 0–100) | ||||
| Pain operated knee | 28.5 (15.0) | 28.3 (15.9) | 28.7 (14.1) | 0.81 |
| Pain non-operated knee | 4.7 (8.1) | 4.7 (7.6) | 4.7 (8.7) | 0.96 |
| Function operated knee | 25.8 (13.8) | 25.3 (14.3) | 26.2 (13.3) | 0.58 |
| Function non-operated knee | 4.2 (8.0) | 4.2 (7.9) | 4.3 (8.1) | 0.98 |
| Functional performance tests | ||||
| Repeated sit-to-stand test (score 0–4) | 3.4 (1.0) | 3.4 (0.9) | 3.4 (1.0) | 0.88 |
| Gait speed, 4 m (s) | 4.4 (0.9) | 4.3 (1.0) | 4.4 (0.8) | 0.33 |
| Physical activity (min MVPA/day) | 42.1 (22.5) | 42.2 (22.0) | 41.9 (23.2) | 0.92 |
| Kellgren-Lawrence grades, n (%), contralateral knee | ||||
| 0 | 57 (21.1) | 29 (21.3) | 28 (20.9) | 0.66 |
| 1 | 62 (23.0) | 33 (24.3) | 29 (21.6) | |
| 2 | 54 (20.0) | 25 (18.4) | 29 (21.6) | |
| 3 | 73 (27.0) | 34 (25.0) | 39 (29.1) | |
| 4 | 24 (8.9) | 15 (11.0) | 9 (6.8) |
Data (n=273) are crude mean (±SD) or n (%). Differences between treatment groups (800 vs 2000 IU vitamin D3) were assessed using Student’s t-test and Wilcoxon test for continuous variables and χ2 test for categorical variables. P values are two-sided; statistical significance was set at p<0.05.
*Preoperative WOMAC function score in the operated knee <52.
MVPA, medium-to-vigorous physical activity; WOMAC, Western Ontario and McMaster Universities Arthritis Index.