Witham, M D, Adams, F, McSwiggan, S et al. · Nutrition, metabolism, and cardiovascular diseases : NMCD · 2015 · DOI
This study tested whether high-dose vitamin D supplements could improve blood vessel health and reduce fatigue in ME/CFS patients, since people with ME/CFS often have low vitamin D levels and poor blood vessel function. Fifty patients received either vitamin D3 (100,000 units every 2 months) or placebo for 6 months. The vitamin D supplements did increase vitamin D levels in the blood, but they did not improve blood vessel stiffness, blood pressure, cholesterol, or fatigue symptoms.
This study directly addresses a common hypothesis that vitamin D deficiency contributes to vascular dysfunction in ME/CFS, a potential therapeutic target. The negative result helps clarify that while vitamin D repletion is measurable and may be clinically appropriate, it alone does not reverse the vascular pathology or symptom burden characteristic of ME/CFS, informing treatment strategies.
This study does not prove that vitamin D supplementation is never beneficial for ME/CFS patients; it only tests one specific dosing regimen (intermittent high-dose) over 6 months and may not capture longer-term effects or benefits in vitamin D–deficient subgroups. It also does not establish whether vitamin D deficiency is a cause or consequence of ME/CFS pathology, nor does it rule out roles for vitamin D in other disease mechanisms not measured here.
About the PEM badge: “PEM required” means post-exertional malaise was an explicit required diagnostic criterion for participant inclusion in this study — not that PEM was studied, observed, or discussed. Studies using criteria that do not require PEM (e.g. Fukuda, Oxford) are tagged “PEM not required”. How the atlas works →
The first block is for the primary paper and is the citation you should use in research work. The atlas-snapshot line only applies if you are specifically referring to this atlas’s reading of the paper on the date shown.
Primary citation
Witham, M D, Adams, F, McSwiggan, S, Kennedy, G, Kabir, G, Belch, J J F, et al. (2015). Effect of intermittent vitamin D3 on vascular function and symptoms in chronic fatigue syndrome--a randomised controlled trial.. Nutrition, metabolism, and cardiovascular diseases : NMCD. https://doi.org/10.1016/j.numecd.2014.10.007
BibTeX
@article{mecfsatlas-witham-2015-effect-intermittent,
author = {Witham, M D and Adams, F and McSwiggan, S and Kennedy, G and Kabir, G and Belch, J J F and Khan, F},
title = {Effect of intermittent vitamin D3 on vascular function and symptoms in chronic fatigue syndrome--a randomised controlled trial.},
journal = {Nutrition, metabolism, and cardiovascular diseases : NMCD},
year = {2015},
doi = {10.1016/j.numecd.2014.10.007},
note = {PubMed: 25455721},
url = {https://www.mecfsatlas.com/evidence/witham-2015-effect-intermittent},
}Atlas snapshot reference
ME/CFS Atlas. Generator v1 / Scanner v1.4 / policy v0.1. Accessed 2026-05-28. https://www.mecfsatlas.com/evidence/witham-2015-effect-intermittent
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