Vitamin D2 (Ergocalciferol)

What the science says

• D3 raises 25(OH)D more effectively than D2 Strong evidence

  A meta-analysis of 10 RCTs found D3 significantly more effective than D2 at raising total 25(OH)D, with the gap widest for bolus dosing. A 12-week randomised food-fortification trial gave 15 µg/day (600 IU) of D2 or D3 to South Asian and white European women through the winter: D3 raised 25(OH)D roughly twice as much as D2 at the identical dose. The mechanism is faster clearance and lower binding affinity of D2 metabolites for vitamin D binding protein.

• D2 still corrects deficiency Moderate evidence

  It does. The standard US prescription for deficiency remains 50,000 IU ergocalciferol weekly for 8–12 weeks, and it works. The practical problems are potency per IU and the faster decline between doses, which makes intermittent high-dose D2 regimens leave larger troughs than equivalent D3 schedules.

• D2 can lower your measured vitamin D level Moderate evidence

  Supplementing with D2 suppresses circulating 25(OH)D3. If your lab uses an older immunoassay that under-detects 25(OH)D2 — many do — your total result can look flat or even fall while you are taking D2 faithfully. If you take D2, ask for an assay (LC-MS/MS) that reports both metabolites.

• D2 and D3 have been compared on clinical outcomes Limited evidence

  They have not, in any meaningful way. The large trials on fracture, respiratory infection and mortality used D3 or pooled both forms without head-to-head comparison. The case for preferring D3 is entirely a biomarker argument — a solid one, but it is not the same as showing D2 produces worse health outcomes.

Dosage & safety

How to take it

Interactions

With medications

• thiazide diuretics

  both raise serum calcium, and the combination can cause hypercalcaemia at ordinary vitamin D doses have calcium checked if you take both

• digoxin

  hypercalcaemia from vitamin D potentiates digoxin toxicity and arrhythmia risk do not take high-dose vitamin D without monitoring

• orlistat and bile-acid sequestrants (cholestyramine, colesevelam)

  they block absorption of fat-soluble vitamins including D separate by at least 2 hours and expect to need a higher dose

• phenytoin, phenobarbital and carbamazepine

  these speed vitamin D breakdown and lower blood levels expect higher requirements and have 25(OH)D measured

With other supplements

• calcium supplements

  vitamin D increases calcium absorption, so high doses of both together raise hypercalcaemia and stone risk keep total calcium under 2,000–2,500 mg/day from all sources

• other vitamin D-containing products (multivitamins, fish oil, D3+K2 combos)

  doses stack silently past the 4000 IU/day upper limit add up the vitamin D across everything you take before adding more

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Scientific references

• Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis
  Tripkovic L, et al. — Am J Clin Nutr, 2012
• Daily supplementation with 15 μg vitamin D2 compared with vitamin D3 to increase wintertime 25-hydroxyvitamin D status in healthy South Asian and white European women: a 12-wk randomized, placebo-controlled food-fortification trial
  Tripkovic L, et al. — Am J Clin Nutr, 2017

Related in Vitamins & minerals

• Vitamin A (Retinol) Moderate evidence
• Vitamin B1 (Thiamine) Moderate evidence
• Vitamin B5 (Pantothenic Acid) Limited evidence
• Vitamin B6 (Pyridoxine) Moderate evidence
• Vitamin K1 Limited evidence
• Calcium Moderate evidence