Table 2.
Depiction of study characteristics regarding dropout rates and adverse reaction to vitamin D supplementation and placebo.
| Study | Participants | Adverse events | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Author | Duration | VitD dosage |
Allocated | Dropout | Clinical causes (VitD: placebo) (% of allocated) |
Lab** | |||||
| Total (n) |
VitD [n (%)] |
Placebo [n (%)] |
Total [n (%)] |
Medical Minor |
Medical serious | Organi-zational* | Not specified | Results | |||
| Parkinson disease | |||||||||||
| Bytowska et al. (2023) | 12 wks | middle | 42 | 8 (38%) | 5 (24%) | 13 (31%) | 10%: 24% | 29%: 0% | |||
| Hiller et al. (2018) | 16 wks | high | 58 | 1 (4%) | 6 (20%) | 7 (17%) | 43%: 67% | 4%: 0% | All neg | ||
| Habibi et al. (2018) | 3 mo | low | 120 | 0 (0%) | 0 | 0 (0%) | – | – | – | – | – |
| Suzuki et al. (2013) | 12 mo | low | 114 | 7 (13%) | 3 (5%) | 10 (9%) | 7%: 2% | 2%: 0% | All neg | ||
| 334 | 16 (10%) | 14 (8%) | 23 (7%) | ||||||||
| Restless legs syndrome | |||||||||||
| Wali et al. (2019) | 12 wks | middle | 35 | 8 (44%) | 5 (29%) | 13 (37%) | 11%: 18% | 11%: 29% | |||
| Total | 369 | 24 (13%) | 19 (10%) | 36 (12%) | n.a. | n.a. | n.a. | n.a. | n.a. | ||
*Organizational adverse events: nonmedical causes for having to discontinue the participation, the most frequent one was the inability to find transport during the COVID pandemic.
**Laboratory screening for abnormal levels of ionized calcium, phosphate, or creatinine, being all in normal recommended limits (all negative).
mo, months; neg, negative; VitD, vitamin D; wks, weeks.