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 →
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