howtosupplement
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

Vitamin D

95
score
A
evidence
Caution
risk

Proven Benefits

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

Chemical Forms

Recommended
  • Vitamin D3 (cholecalciferol)
Avoid
  • Vitamin D2 (ergocalciferol) — often raises 25(OH)D less effectively
Expert Note

D3 is the form your skin makes and the best-studied retail supplement form. Head-to-head trials generally find it raises and maintains 25(OH)D better than D2, so it is usually the more reliable choice for routine supplementation.

Protocol

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

Condition-Based Dosing

Serum 25(OH)D < 20 ng/mL (deficient)
2000-4000 IU daily for 8-12 weeks, then retest.
Serum 25(OH)D 20-30 ng/mL (insufficient)
1000-2000 IU daily.
Adults with obesity or very low sun exposure
2000-4000 IU daily, guided by labs.
Maintenance after reaching target range
1000-2000 IU daily or equivalent 3-5x per week.

Safety & Limits

Upper Safe Limit
4000 IU/day (NASEM/EFSA adult UL)
Cycling
Safe for continuous use

Contraindications

Hypercalcemia — vitamin D can further raise calcium
Sarcoidosis or other granulomatous disease — increased calcitriol production raises toxicity risk
Primary hyperparathyroidism — higher risk of hypercalcemia
Severe chronic kidney disease — dosing and activation may need clinician oversight
Recurrent calcium kidney stones — monitor calcium and urine chemistry
Thiazide diuretics — combined use can raise calcium levels
Digoxin — hypercalcemia can increase arrhythmia risk

Synergies

Magnesium

Magnesium is required for the enzymes that activate vitamin D; low magnesium can blunt the rise in and effects of vitamin D.

Vitamin K2

Vitamin K2 helps activate proteins that direct absorbed calcium into bone rather than soft tissue, especially during long-term vitamin D use.

Calcium

If dietary calcium is very low, vitamin D cannot fully improve calcium balance or bone mineralization.

Avoid Combining With

  • ✕Orlistat (reduces fat absorption — separate by 2+ hours)
  • ✕Bile acid sequestrants like cholestyramine (reduce absorption — separate by 4+ hours)
  • ✕Very low-fat meals (can reduce absorption of fat-soluble vitamin D)
  • ✕Anticonvulsants like phenytoin or carbamazepine (increase vitamin D breakdown)
  • ✕Mineral oil laxatives (reduce fat-soluble vitamin absorption)
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