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VITAMINS

Vitamin D3 (cholecalciferol)

Vitamin D3 supports calcium absorption, strong bones and normal immune function.

Also known as: vitamin D, cholecalciferol, vit D, sunshine vitamin

What the research says

In a study of 163 women low in vitamin D, about 3,200 IU a day for a year nearly tripled blood vitamin D levels.*

RCT (placebo-controlled, 8-arm dose-response) · 163 · Gallagher JC, Ann Intern Med 2012. Read the study on PubMed

Who should be careful

Our safety rules leave vitamin D3 out of a formula, or keep the amount lower, with:

Kept to a lower amount with

• Thiazide water pill
• Calcium oxalate kidney stones more than once, or primary hyperoxaluria
• Kidney stones

Medicines and supplements

• Prescription vitamin D
• Active vitamin D

Health conditions

• High calcium or hyperparathyroidism
• Sarcoidosis or another granulomatous disease

Always check with your doctor or pharmacist before adding a supplement if you take medication, are pregnant or nursing, or have a health condition. Stay under the upper limit from all sources combined, including multivitamins.

Symptoms it’s studied for

• Tired or low energy
• Bloating or gas
• Joint aches or stiffness
• Catching every cold
• Hair shedding
• Skin issues (acne, dry, eczema)
• Muscle cramps or twitches
• Low libido

From the Journal

• Are personalized vitamins worth it? Personalized blend vs a multivitamin

  What a standard multivitamin does well, where it falls short, what research says about personalized nutrition, and how to tell whether a personalized blend makes sense for you.

• How much vitamin D should you take a day?

  The RDA, the 4,000 IU upper limit, IU vs mcg, D3 vs D2, what a 25-hydroxyvitamin D test means, taking it with a meal, the honest evidence on K2, and who should be careful.

• Which blood tests should you check before taking supplements?

  The blood tests that can usefully guide supplements, what each one can and can't tell you, and when to recheck after you change what you take.

• How many supplement pills a day is too many?

  Why adherence drops as daily doses and pill counts rise, how separate bottles double up on the same nutrients and push past upper limits, and how to simplify a supplement routine safely.

• Why am I always tired, and what causes the afternoon crash?

  The everyday reasons for constant tiredness and the 3 pm slump, which blood tests to ask your doctor about, which nutrients have been studied, and the signs that need a doctor soon.

• What is functional medicine, and how does it use supplements?

  What functional and integrative medicine mean, how practitioners use history and labs to choose supplements, and how to judge the evidence and the marketing yourself.

Questions

How much vitamin D3 a day?

apiece formulas usually include 3,000 IU a day. The recommended intake for adults is 600 IU (15 mcg); 800 IU over age 70. Upper limit: 4,000 IU (100 mcg) a day from all sources.

What is vitamin D3 used for?

Vitamin D3 supports calcium absorption, strong bones and normal immune function. In apiece it is part of formulas for Immune support.*

Who should be careful with vitamin D3?

apiece’s safety rules leave it out or limit it with: Thiazide water pill; Calcium oxalate kidney stones more than once, or primary hyperoxaluria; Kidney stones; Prescription vitamin D; Active vitamin D; High calcium or hyperparathyroidism; Sarcoidosis or another granulomatous disease. Check with your doctor or pharmacist if any apply to you.

Can I get vitamin D3 in a personalized supplement?

Yes. apiece builds one daily blend around your goals and, if you have them, your lab results. Vitamin D3 can be part of it at the amount listed, with every ingredient shown and never more than 10 capsules a day.

*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease. This page is general information, not medical advice. Check with your doctor or pharmacist before starting a supplement, especially if you take medication, are pregnant or nursing, or have a health condition. Updated 2026-10-21.