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Evidence-Based Supplement Research
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Vitamin D and Reduced Vitamin D Level

Research synthesisLow evidenceMixed effect size4 studies · 1 beneficial · 1 neutral · 2 harmful

Across 4 studies, 1 reported beneficial, 1 neutral, and 2 harmful effects of Vitamin D on reduced Vitamin D levels, with a predominant effect size that is small to large and mixed. All findings were statistically significant, but study durations and doses were not consistently reported. The strongest evidence (a meta-analysis of psoriasis patients) showed a large harmful association (odds ratio 3.07 for lower vitamin D levels), while other studies in clinical populations showed small to moderate effects in both directions.

  • Studied populations: patients with psoriasis, fibromyalgia, celiac disease, and periodontitis (all clinical populations)

Caveats: Evidence base is small (only 4 studies) — conclusions should be considered preliminary. The only high-quality meta-analysis (evidence score 7) reported a large harmful effect in psoriasis patients, which may skew the overall impression. Most studies observed associations in clinical populations, so results may not generalize to healthy individuals. Study durations and doses were not reported, limiting interpretability of causal effects.

Generated Jul 14, 2026
4 of 4 papers
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