IU vs. μg

Historically, it’s been more common to see vitamin D dosed in international units (IU), rather than micrograms (μg). In 2016, however, the US Food and Drug Administration (FDA) announced that, by 2021, supplement labels had to display vitamin D content in μg.^[1] IU is still commonly seen alongside μg, so it’s good to become familiar with both units: 40 IU is equivalent to 1 μg.

How many grams of vitamin D should I take per day?

The ideal daily dose of vitamin D should correspond to its recommended daily allowance (RDA), which is currently 400–800 IU (10–20 μg) a day, but this may be too low for many adults. For moderate supplementation, a standard daily dose of 1,000–2,000 IU (25–50 μg) of vitamin D3 is sufficient to meet the needs of most people. Higher daily doses are in the range of 20–80 IU (0.5–2 μg) per kilogram of body weight.

Vitamin D should be taken daily with meals or a source of fat.^[2][3]

Regarding the daily recommended dose for babies and children, please refer to the question “Should vitamin D supplements be given to infants and children?”.

What is the ideal daily dose of vitamin D for pregnant women?

The recommended daily dose of vitamin D for pregnant women varies across different countries. In the US, pregnant women are recommended to take 600 IU (15 μg) of vitamin D daily, unless they have a vitamin D deficiency, which will require higher doses.^[4] In the UK, the recommended dosage is slightly lower, 400 IU (10 μg) daily.^[5].

What is the ideal dose of vitamin D for menopausal women?

The recommended daily dose of vitamin D for women during menopause has not yet been established. However, research has shown that daily doses of 2000–4800 IU (50–120 μg) taken regularly were effective at correcting vitamin D deficiencies and maintaining vitamin D levels.^[6]

What is the maximum dose of vitamin D?

The Upper Tolerable Intake Level, which is the maximum daily dose of a nutrient that is unlikely to cause side effects, is 4,000 IU (100 μg) per day in the United States and Canada.^[4] This is considered a high dose of vitamin D; however, doses above this level are sometimes used for short periods of time (e.g., to reverse a severe vitamin D deficiency quickly), with safety likely determined by the dose and duration of supplementation. High-dose vitamin D supplementation should be done under medical supervision in order to monitor blood levels and watch for signs of vitamin D toxicity (e.g., hypercalcemia).

What types of vitamin D are there?

Vitamin D3 supplementation (cholecalciferol) is recommended over D2 supplementation (ergocalciferol), because D3 tends to raise blood levels more effectively.

Vitamin D is usually available in a wide range of doses and forms (e.g., tablets, capsules, soft gels, drops, powder). Which form to choose and how much to take will depend on the vitamin D content in each supplement and the individual’s specific requirements. For instance, for an adult wanting to take 2000 IU (50 μg) a day of vitamin D, the correct daily dose of a vitamin D drops supplement containing 1000 IU (25 μg) per drop would be 2 drops a day.