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

Research synthesisLow evidenceMixed effect size3 studies · 0 beneficial · 1 neutral · 2 harmful

All 3 studies report statistically significant findings that individuals with certain clinical conditions (psoriasis, fibromyalgia, periodontitis) have lower vitamin D levels than controls, indicating a harmful association (lower vitamin D in the condition group). Effect sizes vary from small (fibromyalgia, periodontitis) to large (psoriasis), with the largest effect observed in a meta-analysis of psoriasis (odds ratio 3.07 for low vitamin D, SMD -0.92). No consistent dose or duration data were reported as these are observational comparisons, not intervention trials.

  • Studied populations: clinical populations (psoriasis, fibromyalgia, periodontitis patients vs. healthy controls)

Caveats: Evidence base is small (only 3 studies) — conclusions should be considered preliminary. All studies are observational comparisons, not intervention trials, so causation cannot be established; it is not known whether the condition causes low vitamin D, low vitamin D contributes to the condition, or both. The use of different condition groups and varying effect sizes limit the ability to generalize across populations.

Generated Jun 11, 2026
3 of 3 papers
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