What happened
The study covered 54 adults, mean age about 67, with mild cognitive impairment and sleep problems. Those who reported taking at least 5,000 IU a day of vitamin D scored more than 13% higher on the MoCA cognition test (about 4 points) than those taking no supplement.
Coverage appeared 8 November 2026.
Why it matters
Sleep problems and mild cognitive impairment often arrive together, and vitamin D is cheap and widely taken. A 4-point MoCA gap is large — which is exactly why it needs a trial before anyone acts on it.
What comes next
The author herself calls for a clinical trial before recommending it. Until then, this is a small observational signal, not a dose recommendation.
Observational, 54 people, self-reported dose; it does not prove vitamin D improves memory or prevents dementia. The author calls for a trial before recommending it. Not a high-dose recommendation.