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Table 1 Characteristics according to three groups based on vitamin D level and supplement use

From: Vitamin D supplementation as a potential cause of U-shaped associations between vitamin D levels and negative health outcomes: a decision tree analysis for risk of frailty

  Entire cohort Supplement users Non-users (n = 152)   
  N = 238 n = 86 (36.1%) Low vitamin D (<18 ng/mL) n = 55 (23.1%) High vitamin D (> = 18 ng/mL) n = 97 (40.8%) p value
Frailty Index 0.39 ± 0.13 0.43 ± 0.11 0.41 ± 0.13 0.35 ± 0.13 <0.001
Frailty (FI > =0.25) 208 (87.4%) 84 (97.7%) 50 (90.9%) 74 (76.3%) <0.001
25 (OH) D (ng/mL)
 Mean 23.4 ± 9.8 26.6 ± 9.3 11.7 ± 3.8 27.1 ± 7.0 <0.001
 Range 4–53 6–52 4–17 18–53  
 < 20 ng/mL 89 (37.4%) 19 (22.1%) 55 (100.0%) 15 (15.5%) <0.001
Age 73.4 ± 13.1 79.0 ± 11.7 67.4 ± 12.1 71.9 ± 13.0 <0.001
Body mass index 26.5 ± 6.7 25.1 ± 6.0 29.5 ± 8.5 26.0 ± 5.5 <0.001
Education (year) 13.0 ± 2.3 13.0 ± 2.4 13.0 ± 3.0 13.0 ± 2.3 1.00
Ethnicity
 White 117 (49.2%) 41 (47.7%) 21 (38.2%) 55 (56.7%) 0.03
 Asian/Pacific Islander 102 (42.9%) 41 (47.7%) 30 (54.5%) 31 (32.0%)  
 Others 18 (7.6%) 3 (3.5%) 4 (7.3%) 11 (11.3%)  
Smoking
 Never 80 (33.6%) 27 (31.4%) 13 (23.6%) 40 (41.2%) 0.10
 Past 120 (50.4%) 49 (57.0%) 30 (54.5%) 41 (42.3%)  
 Current 38 (16.0%) 10 (11.6%) 12 (21.8%) 16 (16.5%)  
Alcohol
 Never 100 (42.0%) 39 (45.3%) 20 (36.4%) 41 (42.3%) 0.73
 Past 83 (34.9%) 30 (34.9%) 22 (40.0%) 31 (32.0%)  
 Current 55 (23.1%) 17 (19.8%) 13 (23.6%) 25 (25.8%)  
Reason for admission
 Rehabilitation 86 (36.1%) 26 (30.2%) 24 (43.6%) 36 (37.1%) 0.001
 Skilled-nursing care 49 (20.6%) 7 (8.1%) 15 (27.3%) 27 (27.8%)  
 Intermediate care 8 (3.4%) 4 (4.7%) 1 (1.8%) 3 (3.1%)  
 Respite 95 (39.9%) 49 (57.0%) 15 (27.3%) 31 (32.0%)  
Place veterans came from
 Home 101 (42.4%) 54 (62.8%) 15 (27.3%) 32 (33.0%) <0.001
 Acute care 128 (53.8%) 28 (32.6%) 38 (69.1%) 62 (63.9%)  
 Other nursing home 9 (3.8%) 4 (4.7%) 2 (3.6%) 3 (3.1%)  
Season of admission
 Winter 62 (26.1%) 23 (37.1%) 13 (21.0%) 26 (41.9%) 0.83
 Spring 55 (23.1%) 18 (32.7%) 16 (29.1%) 21 (38.2%)  
 Summer 62 (26.1%) 20 (32.3%) 14 (22.6%) 28 (45.2%)  
 Autumn 59 (24.8%) 25 (42.4%) 12 (20.3%) 22 (37.3%)  
Correlation between FI and 25 (OH) Da −0.10 p = 0.13 −0.05 p = 0.63 −0.19 p = 0.02  
Relative risk of frailty, OR (95% CI) 1.0 (ref) 1.12 (1.05–1.18) p < 0.001 1.04 (0.94–1.15) p = 0.42 0.87 (0.77–0.99) p = 0.03  
  1. Analysis of variance for continuous variables and chi-square test for categorical variables mean ± Standard deviation, n (%)
  2. 25 (OH) D 25-hydroxyvitamin D level, 95%CI 95% confidence interval, FI Frailty Index, OR Odds ratio
  3. aSpearman’s correlation coefficient in supplement users and non-users