TABLE 2.
Percentages of persons in the lowest and highest quantile for serum 25-hydroxyvitamin D [25(OH)D], who were classified into specific latitude regions or quintiles of surrogate markers for vitamin D exposure: sample from the nested case-control studies of the Women's Health Initiative Calcium plus Vitamin D Clinical Trial at enrollment (n = 3055)1
| Agreement | Subjects2 | |
| n (%) | ||
| Latitude of clinic center3 | ||
| Lowest tertile of serum 25(OH)D (n = 1018) | ||
| Northern (>40°N) | Good | 498 (48.9) |
| Northern and Middle (>37°N) | Moderate | 720 (70.7) |
| Southern (≤37°N) | Poor | 298 (29.3) |
| Highest tertile of serum 25(OH)D (n = 1018) | ||
| Southern (≤37°N) | Good | 326 (32.0) |
| Southern and Middle (≤40°N) | Moderate | 548 (53.8) |
| Northern (>40°N) | Poor | 470 (46.2) |
| Langleys [(g-cal)/cm2]3 | ||
| Lowest quintile of serum 25(OH)D (n = 611) | ||
| Lowest quintile (300–325) | Good | 179 (29.3) |
| Lowest 2 quintiles (300–350) | Moderate | 327 (53.5) |
| Highest quintile (475–500) | Poor | 95 (15.6) |
| Highest quintile of serum 25(OH)D (n = 611) | ||
| Highest quintile (475–500) | Good | 152 (24.9) |
| Highest 2 quintiles (400–500) | Moderate | 244 (39.9) |
| Lowest quintile (300–325) | Poor | 184 (30.1) |
| Watts [(J/s)/m2]4 | ||
| Lowest quintile of serum 25(OH)D (n = 611) | ||
| Lowest quintile (0.4–0.5) | Good | 158 (25.9) |
| Lowest 2 quintiles (0.4–0.7) | Moderate | 287 (47.0) |
| Highest quintile (1.5–1.9) | Poor | 70 (11.5) |
| Highest quintile of serum 25(OH)D (n = 611) | ||
| Highest quintile (1.5–1.9) | Good | 84 (13.8) |
| Highest 2 quintiles (1.4–1.9) | Moderate | 236 (38.6) |
| Lowest quintile (0.4–0.5) | Poor | 129 (21.1) |
| Total vitamin D, energy-adjusted (μg/d)5 | ||
| Lowest quintile of serum 25(OH)D (n = 566)6 | ||
| Lowest quintile (0.09–3.10) | Good | 229 (40.5) |
| Lowest 2 quintiles (0.09–5.28) | Moderate | 364 (64.3) |
| Highest quintile (14.96–78.77) | Poor | 40 (7.1) |
| Highest quintile of serum 25(OH)D (n = 585)6 | ||
| Highest quintile (14.96–78.77) | Good | 174 (29.7) |
| Highest 2 quintile (>10.40–78.77) | Moderate | 301 (51.5) |
| Lowest quintile (0.09–3.10) | Poor | 76 (13.0) |
Serum vitamin D was adjusted for month of blood draw by regressing 25(OH)D on month of blood draw to compute residuals and adding the residuals to the mean serum 25(OH)D concentration in the sample. A weighted κ statistic, obtained by using the Cicchetti-Allison method for computing weights, was computed to compare the agreement (beyond chance) between quantiles of 25(OH)D and the surrogate measures for vitamin D status (38).
Percentage equals n/total n.
Weighted κ = 0.02
Weighted κ = 0.03
Weighted κ = 0.19
Of 3055 participants, 190 were missing data on total vitamin D intake.