Vitamin d Mega-Dose tested to fight memory loss in seniors

NCT ID NCT03613116

Ongoing Disease control Sponsor: University of California, Davis Source: ClinicalTrials.gov ↗

First seen Jun 27, 2026 · Last updated Jun 27, 2026

Summary

This Phase II trial tests whether high-dose vitamin D (4,000 IU daily) can correct deficiency and slow cognitive decline better than standard doses in 180 older adults aged 65-90. Participants include those with normal thinking, mild impairment, or early Alzheimer's. The study lasts 3.5 years and uses brain scans and thinking tests to measure effects.

What this could mean

Our plain-language read of the trial. This is informational only — not medical advice or a prediction.

Active substance: Vitamin D3 (cholecalciferol) as a dietary supplement
What this could lead to: If successful, this could point toward a simple, low-cost way to slow cognitive decline in older adults with vitamin D deficiency.
What could go wrong: This is a Phase II trial with only 180 participants, so results may not apply to everyone. It tests cognitive effects as a secondary outcome, so it may not show clear benefit.

This is an AI summary of the original study and may miss details. Read our disclaimer.

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Conditions

The condition(s) this trial relates to.

Alzheimer disease Cognitive Dysfunction vitamin D deficiency

As listed by the trial registrant

The condition terms exactly as the trial's registrant entered them.

COGNITIVE DECLINE VITAMIN D DEFICIENCY

Contacts and locations

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Locations

University of California, Davis Alzheimer's Disease Center

Walnut Creek, California, 94598, United States

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