Vitamin D3
Cholecalciferol, the strongest evidence in the bottle. Daily or weekly dosing lowers respiratory infection risk, most in people who start out low.
Written by R. Kessler · About Knurle · Editorial policy
The short answer
A pooled analysis of 25 randomised trials in nearly 11,000 people found daily or weekly vitamin D lowered the risk of acute respiratory infection, with the largest effect in people who were already deficient. One large occasional dose did not produce the same benefit.
The form, and why it matters
Cholecalciferol is D3, the form skin makes from sunlight and the form most supplements use. Ergocalciferol is D2, the plant-derived form, and it raises serum 25(OH)D less reliably per microgram, which is why D3 is the default.
Typical dose
The adult reference intake is 15 mcg (600 IU) up to age 70 and 20 mcg (800 IU) after, with a tolerable upper intake of 100 mcg (4,000 IU). Moat carries 40 mcg and Keel 50 mcg, both daily, which matches the dosing pattern the pooled trial data favoured.
What the research shows
The individual participant data meta-analysis pooled 25 randomised, double-blind, placebo-controlled trials covering close to 11,000 people. Daily and weekly dosing lowered respiratory infection risk; large infrequent boluses did not. The effect was largest in participants who started out deficient.
Who should be careful
Because D is fat soluble it accumulates, and very high intakes over months can cause calcium to rise to a harmful level. If a clinician has set you a dose for a diagnosed deficiency, theirs wins.
Where it sits in our formulas
| Product | Form on the label | Amount per serving | % Daily Value |
|---|---|---|---|
| Moat | as cholecalciferol | 40 mcg | 200% |
| Keel | as cholecalciferol | 50 mcg | 250% |
Sources
- Martineau et al., Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and individual participant data meta-analysis, BMJ
- NIH Office of Dietary Supplements, Vitamin D fact sheet
Figures checked against the sources above on 21 September 2026.
Vitamin C
Ascorbic acid at 180 mg a day. Regular supplementation does not stop you catching a cold; it modestly shortens the one you caught.
Read itZinc
Zinc citrate in Moat at the everyday nutritional amount, zinc bisglycinate in Keel. The famous cold trials used lozenges at 80 to 207 mg, which is a different thing entirely.
Read itMagnesium
200 mg as oxide plus citrate. Magnesium draws water into the bowel, which is why the oxide form is the one that helps constipation.
Read itVitamin D in winter: the quiet overachiever
Vitamin D has the strongest evidence of anything in the bottle, and it is not close. What 25 trials and 11,000 people showed about winter dosing, and why daily beats a single big dose.
Read itCan GLP-1 Medications Cause Vitamin Deficiency?
GLP-1 medications like Ozempic and Mounjaro can lead to lower nutrient intake and absorption, raising risk of deficiencies in key vitamins and minerals.
Read itEvery milligram, printed.
Each amount on the label is the amount in a full daily serving, and it matches what is on this page.
