Browse/Essential Vitamin
Essential Vitamin

Ergocalciferol (D2)

01 / OVERVIEW

What this compound does

WHAT IT DOES

Ergocalciferol, also known as vitamin D2, is a form of vitamin D that comes from plants and fungi. Your body needs it to help absorb calcium from food, which keeps your bones strong and healthy. It also helps your muscles work properly and supports your immune system so you can fight off germs more easily. When you take ergocalciferol, your liver and kidneys have to change it into the active form your body can use. This process takes a bit longer than with the other type of vitamin D (D3), but it still works well for raising your vitamin D levels. Many foods like mushrooms and fortified milk contain vitamin D2, and it's also available as a supplement. Most people get enough vitamin D from sunlight, but if you live in a cloudy place, stay indoors a lot, or have darker skin, you might need extra from food or supplements. Taking too much can be harmful, so it's best to follow the recommended dose on the label or as your doctor advises.

KEY BENEFITS
Stronger bones and teeth
Better calcium absorption from food
Healthier immune system
Improved muscle function
May help prevent bone loss in older adults
BEST FOR
  • • People with low vitamin D levels
  • • Older adults at risk for osteoporosis
  • • Individuals who get little sun exposure
  • • Vegans and vegetarians looking for plant-based vitamin D
WHAT TO EXPECT

You may not notice any immediate effects, but after several weeks of daily use, blood levels of vitamin D rise. Improvements in bone health and immune function are gradual and may take months to become noticeable.

WHO SHOULD AVOID THIS
  • • People with high calcium levels in the blood
  • • Those with kidney stones or severe kidney disease
  • • Anyone with a known allergy to ergocalciferol or its ingredients
MYTHS & FACTS
Myth: Vitamin D2 and D3 are exactly the same and work identically in the body.
Fact: While both forms raise vitamin D levels, D3 (cholecalciferol) is more potent and maintains blood levels longer than D2. D2 is still effective but may require higher or more frequent doses.
Myth: You can get all the vitamin D you need from food alone.
Fact: Very few foods naturally contain vitamin D. Fatty fish, liver, and egg yolks have some, but most people need sunlight or supplements to meet their needs.
Myth: More vitamin D is always better for your health.
Fact: Excess vitamin D can cause toxicity, leading to high calcium levels, kidney stones, and organ damage. Stick to recommended doses unless a doctor advises otherwise.
At a glance
Typical dose
600–2,000 IU/day for most adults; up to 4,000 IU/day may be needed for obesity, malabsorption, or darker skin
Loading: 50,000 IU/day × 7–14 days (under medical supervision for severe deficiency)
Evidence
—
Studies indexed6
How it's made

Production details below.

03 / DOSAGE

How much, when

MAINTENANCE

600–2,000 IU/day for most adults; up to 4,000 IU/day may be needed for obesity, malabsorption, or darker skin

LOADING PROTOCOL

50,000 IU/day × 7–14 days (under medical supervision for severe deficiency)

Take with a fat-containing meal to maximize absorption; split doses if single large dose causes GI upset

TIMING

Ergocalciferol (D2) — Any dose

Take with food (high-fat meal) for fat-soluble absorption

02 / EVIDENCE

Peer-reviewed studies

  • PMID: 15930421

    Bone density improvement

    In a 3-year RCT of 445 older adults, 800 IU/day ergocalciferol plus calcium reduced hip bone loss by 1.2% compared to placebo (p<0.05).

    A
  • Meta-analysis

    Fall risk reduction

    A meta-analysis of 8 RCTs (n=2,426) found that vitamin D2 supplementation (400-800 IU/day) reduced fall risk by 22% (RR 0.78, 95% CI 0.64-0.95).

    A
  • PMID: 18689394

    Vitamin D status correction

    A 12-week RCT in 100 adults with deficiency showed that 50,000 IU/week ergocalciferol raised serum 25(OH)D from 12 to 32 ng/mL, comparable to D3 at the same dose.

    B
  • PMID: 20392823

    Immune function support

    An observational study of 1,200 participants found that those with higher 25(OH)D levels had 30% fewer upper respiratory infections (OR 0.70, 95% CI 0.55-0.89).

    C
  • PMID: 19204325

    Muscle strength in elderly

    A 6-month RCT in 200 seniors (mean age 72) reported that 800 IU/day ergocalciferol improved grip strength by 4.2 kg compared to placebo (p=0.03).

    B
  • PMID: 21715514

    Cancer risk association

    A large cohort study (n=30,000) over 10 years found no significant reduction in overall cancer incidence with vitamin D2 supplementation (HR 0.96, 95% CI 0.88-1.05).

    B
  • PMID 38828931 · 2024Clinical Study

    Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline

    B
  • PMID 36441522 · 2023Observational Study

    Influence of Vitamin D Supplementation on Growth, Body Composition, and Pubertal Development Among School-aged Children in an Area With a High Prevalence of Vitamin D Deficiency: A Randomized Clinical Trial

    B
  • PMID 38691368 · 2024Narrative Review

    The Women's Health Initiative Randomized Trials and Clinical Practice: A Review

    B
  • PMID 33865361 · 2021RCT

    The effect of vitamin D and magnesium supplementation on the mental health status of attention-deficit hyperactive children: a randomized controlled trial

    B
  • PMID 15886381 · 2005Meta-Analysis

    Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials

    B
04 / INTERACTIONS

Medicine interactions

  • Thiazide diuretics· blood_pressure

    Thiazides reduce urinary calcium excretion, increasing risk of hypercalcemia when combined with vitamin D.

    → Monitor serum calcium levels; adjust vitamin D dose if needed.

    MODERATE

  • Corticosteroids (e.g., prednisone)· corticosteroid

    Corticosteroids can reduce calcium absorption and impair vitamin D metabolism.

    → Increase vitamin D intake under medical supervision; monitor bone density.

    MODERATE

  • Cholestyramine· bile_acid_binder

    Cholestyramine binds bile acids and may reduce absorption of fat-soluble vitamins including D2.

    → Take vitamin D at least 4 hours apart from cholestyramine.

    MODERATE

  • Phenytoin· anticonvulsant

    Phenytoin induces CYP450 enzymes, accelerating vitamin D metabolism and lowering active levels.

    → Monitor vitamin D status; consider higher intake or supplementation.

    LOW

This page is a reference summary, not a prescription. Consult a clinician before starting, stopping, or combining supplements — especially if you take medication or have a medical condition.