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Deficiency/Longevity/Immunity

Vitamin D

Fat-soluble vitamin that corrects low vitamin D status and supports bone and immune health in adults with low sun exposure.

Vitamin D
95
score
A
evidence
Caution
risk

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Use with caution

This supplement may interact with medications, medical conditions or sensitive populations. Review safety before use.

Quick Take

Worth it if you get little sun or test low — strong for deficiency correction, modest beyond that.

Vitamin D is a fat-soluble vitamin made in skin after sun exposure and found in fatty fish, egg yolks, fortified dairy, and UV-exposed mushrooms. In the body it is converted to calcitriol, a hormone-like compound that regulates calcium and phosphorus balance and gene signaling in bone, muscle, and immune cells. Best-supported uses are correcting low vitamin D status, supporting bone and muscle function, and modestly lowering respiratory infection risk. It helps most people with low sun exposure or low blood levels.

Potential benefits

01
Corrects vitamin D deficiency
02
Supports bone health
03
Reduces respiratory infection risk
04
Improves muscle function
05
May reduce depressive symptoms
06
May lower CRP and IL-6
07
May improve insulin sensitivity

Protocol

Amount
1000-2000 IU
Frequency
Once daily
When
With a meal containing fat to improve absorption.

Onset Time

2-4 weeks if deficient; 8-12 weeks for blood level change

Who Should Consider

Adults with little midday sun exposure
People with darker skin at higher latitudes
Adults 50+ who spend most time indoors
People with overweight or obesity
People with confirmed 25(OH)D < 30 ng/mL

Food Sources

  • Salmon or sardines (~300-600 IU per 100 g)
  • Cod liver oil (~1300 IU per teaspoon)
  • Egg yolks (~40 IU each)
  • Fortified milk (~100-120 IU per cup)
  • Fortified plant milk (~100-150 IU per cup)
  • UV-exposed mushrooms (~400 IU per 100 g, mostly D2)

How It Works

Vitamin D is converted in the liver to 25(OH)D and then in the kidney and other tissues to calcitriol. Calcitriol binds the vitamin D receptor to increase intestinal calcium and phosphorus absorption and alter gene expression in bone, muscle, and immune cells.

Updated 5/19/2026

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