The evidence

Backed by the research, not the hype.

Every On Call formula starts in the clinical literature. Here is the evidence behind the two doses we chose, and the reasoning our physicians used to choose them.

One study is a headline. The evidence is a pattern.

We don't formulate around a single sponsored trial. Every dose we ship has to hold up across the weight of the published research, reviewed by board-certified physicians in internal medicine and neurology.

01 / Vitamin D3

2,000 IU, in the middle of the window.

There is a window for vitamin D. Too little and you stay short. Too much and you pass the safe ceiling with no added benefit. We dose to the middle of it.

The NIH puts the adult RDA at 600 IU and the tolerable upper limit at 4,000 IU per day. We chose 2,000 IU, the same daily dose used in VITAL, the largest randomized vitamin D trial ever run, where more than 25,000 adults took it for over five years.2 It is a meaningful amount that stays comfortably inside the safe range.

The vitamin D3 window

ON CALL 2,000 IU RDA 600 IU Upper limit 4,000 IU Shaded band = effective and within the safe range set by the NIH.

We also use D3, not D2. Head to head, cholecalciferol (D3) raises and holds blood levels of vitamin D more reliably than ergocalciferol (D2).1 Our D3 is plant-based, sourced from lichen and algae, which make the exact same cholecalciferol molecule your skin produces in sunlight. Fully vegan, with nothing lost along the way.

From source to your bloodstream

Lichen & algae, or sunlight on skin
→
Cholecalciferol (D3)
→
Liver converts it
→
25(OH)D your body uses

02 / Vitamin B12

500 mcg, where the curve levels off.

B12 is the one most labels get wrong in the other direction. The RDA is only 2.4 mcg, so a 5,000 mcg label looks absurd. There is a catch, though: only a small fraction of an oral dose is absorbed by passive diffusion, so the number on the label and the amount your body takes up are not the same.

In a dose-finding trial, daily oral cyanocobalamin reached most of its effect on B12 status at around 500 mcg, with little added benefit above it.3 That is exactly where we set the dose. Trials also show that oral B12 at these amounts restores levels as well as an injection for most people.4

Effect on B12 status by daily oral dose

16% 2.5 16% 100 23% 250 33% 500 ON CALL 33% 1,000 mcg per day MMA reduction

Reduction in methylmalonic acid, a blood marker that rises when B12 runs low, after 16 weeks of daily oral cyanocobalamin. The effect plateaus near 500 mcg. Adapted from Eussen et al., 2005.3

How we work

How we choose a dose.

1

Start with the clinical literature, never a trend.

2

Find the amount the body can actually use.

3

Confirm it stays below the safe upper limit.

4

Formulate, then third-party test every batch.

References

  1. Tripkovic L, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status. Am J Clin Nutr. 2012;95(6):1357-1364. PMID 22552031
  2. Manson JE, et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease (VITAL). N Engl J Med. 2019;380(1):33-44. PMID 30415629
  3. Eussen SJ, et al. Oral cyanocobalamin supplementation in older people with vitamin B12 deficiency: a dose-finding trial. Arch Intern Med. 2005;165(10):1167-1172. PMID 15911731
  4. Vidal-Alaball J, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2005;(3):CD004655. Cochrane CD004655
  5. National Institutes of Health, Office of Dietary Supplements. Vitamin D and Vitamin B12 Health Professional Fact Sheets. ods.od.nih.gov

Read it, then try it.

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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. The studies referenced inform our formulation choices and do not constitute a claim about any specific health outcome.