Vitamin D Dosage: What the Guidelines Say

Vitamin D is fat-soluble and accumulates in the body, which is why it carries an established upper intake level and why high-strength products deserve more care than most supplements on the shelf.

Recommended intakes differ by country

National authorities set their own figures and they do not all agree. The NIH Office of Dietary Supplements publishes the US recommended dietary allowances by age; the NHS and the HSE publish guidance for the UK and Ireland, which includes seasonal advice reflecting latitude. If you are reading a dose recommendation online, check which country it applies to.

The upper limit

There is a tolerable upper intake level for vitamin D, above which the risk of adverse effects increases. It applies to total intake from all sources. Because vitamin D is stored rather than excreted readily, sustained intake above the limit is the concern rather than a single high dose.

Excess vitamin D can raise blood calcium, and the consequences of that are clinical rather than trivial. This is the main reason very high-strength products should not be taken daily on the basis of internet advice.

Products span a twenty-five-fold range

Our catalogue carries products from 400 IU to 10,000 IU per softgel, and preparations at 50,000 IU exist for intermittent regimens. These sit on the same shelf in similar packaging. The strength filter on our vitamin D comparison sorts them numerically so the spread is visible.

Test rather than guess

Vitamin D status is measured with a blood test for 25-hydroxyvitamin D. Deficiency is diagnosed on that basis, not from a list of symptoms — and if you are considering a high-dose product because you suspect you are deficient, the test is the step that should come first. Your doctor can interpret the result against your history, which a reference range alone cannot.

Add up everything you take

Multivitamins, combined calcium products, cod liver oil and fortified foods all contribute. Read IU vs mcg first so you are adding comparable numbers.

Speak to a professional if

You are considering a dose above the label instruction; you have a condition affecting calcium, the kidneys, the parathyroid glands, or granulomatous disease such as sarcoidosis; you are pregnant or breastfeeding; you are buying for a child; or you take regular medication. Please read our medical disclaimer.

References

• NIH Office of Dietary Supplements — Vitamin D (Health Professional Fact Sheet)
• NHS — Vitamin D
• Health Service Executive (Ireland) — Vitamin D
• NIH Office of Dietary Supplements — Nutrient Recommendations and Databases