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Fat-soluble vitamin

Vitamin D

D2 / D3

Calcium and phosphorus absorption, bone mineralization, muscle and immune function

Essential nutrient

Reference intakes (RDA or AI) are set by the National Academies of Sciences, Engineering, and Medicine. Deficiency thresholds come from clinical and WHO guidance.

At a glance

Women, 19-50
15 mcg (600 IU); 20 mcg (800 IU) if 71+
Men, 19-50
15 mcg (600 IU); 20 mcg (800 IU) if 71+
Upper limit (adults)
100 mcg (4,000 IU)/day
How common is deficiency?
COMMON - one of the most widespread deficiencies worldwide, especially in winter/northern latitudes

Food sources

Animal sources
Fatty fish (salmon, trout, mackerel, sardines), cod liver oil, egg yolk, beef liver, fortified milk
Plant sources
UV-exposed mushrooms (D2), fortified plant milks, fortified cereals/orange juice; sunlight on skin is the main source

Deficiency and testing

Signs of deficiency
Bone pain, muscle weakness, fatigue, frequent fractures; rickets in children; osteomalacia in adults; low mood reported
Who is at higher risk
Dark skin, limited sun exposure, older adults, obesity, exclusively breastfed infants without supplement, malabsorption, covered clothing
How it is tested
Serum 25-hydroxyvitamin D [25(OH)D] by LC-MS/MS or immunoassay; supporting: PTH, serum calcium/phosphate, alkaline phosphatase
Cut-offs
25(OH)D <12 ng/mL (30 nmol/L) = deficiency (IOM/NIH); <20 ng/mL (50 nmol/L) = inadequate/insufficient per Endocrine Society and many labs

Symptoms are not specific. Only a clinician with the right tests can tell whether you are deficient.

Supplement forms

Common forms
D3 (cholecalciferol), D2 (ergocalciferol), calcifediol (25-OH D, prescription), drops, softgels, gummies, sprays, high-dose injections/prescription.
More effective
D3 with a fat-containing meal (raises and sustains blood 25(OH)D better than D2 in most trials); oil-based softgels/drops; calcifediol when absorption is poor (obesity, liver or gut disease). Vegan D3 (from lichen) works as well as animal D3.
Less effective
D2 at the same dose (shorter-lasting effect); dry tablets without a meal; gummies and sprays (dose can vary; limited head-to-head data); sunscreen-blocked or winter sun as the only source.

Safety, interactions and halal notes

Safety and interactions
Upper limit for adults: 100 mcg (4,000 IU)/day. Going above the upper limit over time can cause harm, so check labels and talk to a clinician before high-dose supplements.
Halal note
Vitamin D3 is commonly made from lanolin (sheep wool) or lichen, and often comes in gelatin softgels. Check the source and the capsule shell, and ask for the halal certificate. This is general guidance, not a certification.

Frequently asked questions

How much Vitamin D do adults need per day?

Women 19-50: 15 mcg (600 IU); 20 mcg (800 IU) if 71+. Men 19-50: 15 mcg (600 IU); 20 mcg (800 IU) if 71+. Upper limit: 100 mcg (4,000 IU)/day. Needs change with age, pregnancy and health conditions.

What are the signs of Vitamin D deficiency?

Bone pain, muscle weakness, fatigue, frequent fractures; rickets in children; osteomalacia in adults; low mood reported. These signs are not specific, so only a clinician with the right tests can confirm a deficiency.

What are the best food sources of Vitamin D?

Animal sources: Fatty fish (salmon, trout, mackerel, sardines), cod liver oil, egg yolk, beef liver, fortified milk. Plant sources: UV-exposed mushrooms (D2), fortified plant milks, fortified cereals/orange juice; sunlight on skin is the main source.

Which form of Vitamin D supplement is best?

D3 with a fat-containing meal (raises and sustains blood 25(OH)D better than D2 in most trials); oil-based softgels/drops; calcifediol when absorption is poor (obesity, liver or gut disease). Vegan D3 (from lichen) works as well as animal D3.

Sources

  1. NIH Office of Dietary Supplements fact sheet
  2. National Academies: Dietary Reference Intakes

← Back to the full nutrient guide

This page is for education only and is not medical advice. These statements have not been evaluated by the Food and Drug Administration. Supplements are not intended to diagnose, treat, cure or prevent any disease. Talk to a qualified clinician before starting a supplement, especially if you are pregnant, breastfeeding, take medicine or have a medical condition. Daily needs are US reference intakes for adults 19-50.

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