Why does On Call D3 use D3 instead of D2?

Vitamin D supplements commonly use one of two forms: vitamin D2, called ergocalciferol, or vitamin D3, called cholecalciferol. On Call D3 uses vitamin D3 from algae.

Human research comparing the two forms, rather than the largest number on a bottle, supports that choice.

What is the practical difference between vitamin D2 and D3?

Both forms contribute vitamin D. The useful question is whether they change the blood marker used to assess vitamin D status in the same way.

The National Institutes of Health Office of Dietary Supplements identifies a blood marker as the main way vitamin D status is assessed. It also notes research comparing D2 and D3, including systematic-review evidence and controlled trials.

One 12-week randomized, double-blind, placebo-controlled trial studied 335 healthy South Asian and white European women during winter. Participants received the same daily amount, 15 micrograms, of either D2 or D3 in fortified foods, or placebo. The D3 groups had a greater increase in the vitamin D blood marker than the D2 groups.

The point is narrow but useful: at the same studied amount, D3 moved the laboratory marker more than D2 in that trial.

Does that mean more vitamin D is always better?

A comparison between forms does not choose an individual dose. A higher blood result also does not automatically prove a better health outcome.

Dose still depends on the person, the product, total intake, and clinical context. Questions about symptoms, medications, pregnancy, laboratory results, or a diagnosed deficiency belong with a physician who knows the full history.

Why does On Call D3 use algae-derived D3?

On Call D3 was designed around vitamin D3 rather than D2. The form has stronger evidence for raising and maintaining the blood marker used to assess vitamin D status. Algae provides a vegan source of D3, which fits the product without changing the evidence question.

Each On Call D3 gummy contains 50 micrograms, or 2,000 IU, of vitamin D3. The selected amount and the gummy format are separate decisions from the D2 versus D3 comparison.

What did the study not show?

The trial did not establish a personal dose for every adult. It did not show that a higher result is always preferable. It did not turn a laboratory marker into a promise about symptoms or outcomes.

Good evidence is most useful when its boundary stays visible. Here, the evidence supports the form choice. It does not replace individual medical judgment.

Sources

1. Tripkovic L, et al. Randomized comparison of daily vitamin D2 and vitamin D3 in healthy South Asian and white European women. American Journal of Clinical Nutrition. 2017;106(2):481-490. PMID 28679555. https://pubmed.ncbi.nlm.nih.gov/28679555/
2. National Institutes of Health Office of Dietary Supplements. Vitamin D, Health Professional Fact Sheet. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/

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.