Across 4 studies on vitamin D for reducing vitamin D deficiency, 2 reported beneficial effects (moderate and large) and 2 reported neutral effects (small). The predominant effect size is mixed (small to large). A 2025 RCT in children with inflammatory bowel disease found that both 2000 IU daily and stoss protocols significantly increased 25OHD levels over 12 months. The median study duration was 273 days (approximately 9 months).
Studied populations: clinical (children with inflammatory bowel disease), pregnant women
Caveats: Evidence base is small (only 4 studies) — conclusions should be considered preliminary. Many of the included studies did not reach statistical significance — effect may be smaller than the predominant direction suggests. One study focused on a pediatric inflammatory bowel disease population and another on pregnant women; results may not generalize to healthy adults or other populations.
Generated Jun 15, 2026
Doses used in studies
IU single-dose: 2,000–800,000 (median 401,000, IQR 2,000–800,000)— 1 study
Time to effect
Median: 9.1 months · IQR 7.5 months–10.6 months · Range 6 months–12.2 months— Reported in 2 of 4 studies
Safety in these studies
Overall tolerabilityReported
The study does not report any adverse events, side effects, or safety findings related to the intervention.
Vitamin D deficiency (86.5% vs. 13.5%; p = 0.985) ... were more predominant among pregnant women with inadequate dietary pattern, however not statistically significant