Table 1. Characteristics of the twins as a function of season.
| Total (n = 204) | Summer season (n = 148) | Winter season (n = 56) | |
| Mean (SD) | Mean (SD) | Mean (SD) | |
| S-25-hydroxyvitamin D2+3 (nmol/L) | 84.8 (27.4) | 91.2 (26.2) | 67.2 (22.8) |
| S-25-hydroxyvitamin D3 (nmol/L) | 83.3 (27.4) | 89.6 (26.3) | 65.9 (22.8) |
| S-1,25-dihydroxyvitamin D (pmol/L) | 117.4 (43.5) | 123.8 (45.2) | 99.7 (32.7) |
| Age (years) | 57.5 (9.7) | 56.3 (7.1) | 60.6 (14.3) |
| Weight (kg) | 74.0 (12.2) | 75.0 (12.5) | 71.0 (10.7) |
| Height (cm) | 170.5 (9.7) | 171.6 (9.6) | 167.5 (9.4) |
| Body mass index (kg/m2) | 25.4 (3.2) | 25.4 (3.1) | 25.3 (3.4) |
| P-PTH (pmol/L) | 1.9 (0.9) | 2.0 (1.0) | 1.9 (0.9) |