Vitamin D3

Cholecalciferol · Vitamin D

Snapshot

Indications	Contraindications
Vitamin D deficiency¹ Rickets and osteomalacia prevention¹ Preeclampsia risk in pregnancy^2–4 Progression of prediabetes^4–6 Childhood asthma exacerbations⁷ Depressive symptoms^8–10	High blood calcium¹¹ Kidney stones¹¹ Thiazide diuretics¹

Vitamin D3 (cholecalciferol) is the fat-soluble form made in skin on sun exposure and found in fatty fish, fortified foods, and supplements¹. After activation it promotes calcium absorption and bone mineralization¹. Supplementation is used to correct low status and support bone health, and also in pregnancy, prediabetes, and for immune function, where the trials are few¹. Typical patients are older adults and people with limited sun exposure, dark skin, fat malabsorption, obesity, or gastric bypass¹.

Evidence splits by outcome. A large randomized trial in generally replete older adults found no effect on fractures, cancer, or cardiovascular events. Meta-analyses link supplementation to less preeclampsia in pregnancy and less progression from prediabetes to diabetes. A 2022 randomized trial in older adults found fewer confirmed autoimmune diagnoses with supplementation¹². Products supply D3 or D2, and D3 raises circulating 25-hydroxyvitamin D more than D2¹³; softgels, capsules, and gummies, often paired with calcium, are common (see Form comparison).

The caution centers on hypercalcemia, because vitamin D increases intestinal calcium absorption and excess intake can progress to kidney injury¹. Thiazide diuretics reduce urinary calcium excretion, so combining them with vitamin D may raise calcium, especially in older adults¹. Memorial Sloan Kettering guidance directs patients taking diuretics to talk with their healthcare provider¹¹.

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

65 sources, 49 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources