Vitamin D3
Vitamin D3 (cholecalciferol) is a fat-soluble secosteroid produced in the skin when exposed to UVB radiation from sunlight. It can also be obtained through fatty fish, fortified foods, and supplements. Deficiency is remarkably common worldwide, particularly in higher latitudes, and the vitamin plays well-documented roles in calcium metabolism, immune regulation, and neurological function.
Research Evidence
May support cognitive function and brain health when levels are adequate
ModerateSupports healthy immune system regulation
StrongImproves mood and may reduce depressive symptoms in deficient individuals
ModerateSupports calcium absorption and bone mineral density
StrongAssociated with improved heart rate variability markers
LimitedReduces risk of respiratory infections
StrongExpert Evidence
233 references from 6 experts
“I already take 1,000 international units as part of micro vitamin.”
Vitamin D — I Was Wrong
10:4492 references in 34 episodes from 2021–2025
Safety & Cautions
Side Effects
- Hypercalcemia at very high doses
- Nausea or appetite loss with excess intake
- Kidney stones with prolonged high-dose use
- Elevated blood calcium causing fatigue or confusion
Vitamin D3 is generally well-tolerated at standard supplemental doses. However, chronic intake above 10,000 IU daily without medical supervision can lead to toxicity through excess calcium accumulation, so periodic blood testing is advisable for those on higher doses.
Pairs Well With
Price Comparison
From $0.03/ct
N
Nature MadeBest Value
4.8
•300 ct$0.03/ct
$7.64 total
N
NatureWise
4.8
•360 ct$0.04/ct
$14.99 total
N
NOW Foods
4.8
•240 ct$0.04/ct
$8.54 total
N
Nutricost
4.8
•240 ct$0.05/ct
$12.95 total
N
Nature's Bounty
4.8
•150 ct$0.04/ct
$5.41 total
T
Thorne
4.8
•60 ct$0.33/ct
$20.00 total