Table 4.
Effect of vitamin C supplementation on subjective vitality
| Vitamin C (n = 24) | Placebo (n = 22) | Vitamin C vs. placebo | ||||||
|---|---|---|---|---|---|---|---|---|
| Baseline | Endpoint | Changea | Baseline | Endpoint | Change | Difference in change (95% CI) | Pb | |
| Fatigue | 9.3 ± 2.4 | 7.8 ± 2.7 | − 1.5 ± 2.5** | 8.9 ± 2.1 | 8.9 ± 1.9 | − 0.05 ± 2.6 | − 1.5 (− 3.0, 0.1) | 0.06 |
| Attention | 7.1 ± 1.8 | 9.0 ± 2.4 | 1.9 ± 2.7** | 7.7 ± 2.1 | 8.0 ± 2.0 | 0.3 ± 2.5 | 1.6 (0.1, 3.2) | 0.03 |
| Work engagement | 68.7 ± 14.9 | 74.4 ± 16.1 | 5.8 ± 10.2* | 74.3 ± 13.9 | 74.7 ± 14.1 | 0.4 ± 9.7 | 5.3 (− 0.6, 11.3) | 0.07 |
| Vigor | 23.2 ± 5.7 | 25.8 ± 6.0 | 2.5 ± 4.2** | 25.4 ± 5.4 | 27.0 ± 5.7 | 1.5 ± 4.0 | 1.0 (− 1.4, 3.4) | 0.41 |
| Dedication | 23.0 ± 6.8 | 24.1 ± 6.6 | 1.0 ± 4.0 | 24.5 ± 5.3 | 23.9 ± 5.4 | − 0.6 ± 4.1 | 1.7 (− 0.7, 4.1) | 0.16 |
| Absorption | 22.4 ± 4.9 | 24.6 ± 5.5 | 2.2 ± 4.0* | 24.3 ± 5.1 | 23.8 ± 5.9 | − 0.5 ± 4.1 | 2.7 (0.3, 5.1) | 0.03 |
| Self-control resources | 16.5 ± 4.3 | 18.5 ± 5.3 | 2.0 ± 4.7* | 16.1 ± 4.1 | 17.5 ± 4.4 | 1.4 ± 4.8 | 0.5 (− 2.3, 3.3) | 0.72 |
Values are presented as mean ± SD
There were no significant differences between the vitamin C group and the placebo group for all variables measured at the baseline (all p > 0.05; unpaired t test)
aBaseline and endpoint (week 4) measures differed significantly within the vitamin C group (*p < 0.05, **p < 0.01; paired t test)
bA repeated-measures ANOVA with Bonferroni correction was used to determine the time-by-group interaction with time as the within-subject factor and treatment (vitamin C versus placebo) as the between-subject factor