Immunity hub
What the trials say about NAC, zinc, vitamin D, vitamin C, elderberry and probiotics, graded honestly, including the nulls.
Education only, not medical advice.
Immunity hub
Vitamin D and respiratory infections
Modest protection in pooled trials, mostly with daily dosing and in people who start low. Large recent trials were null.
5 min · 4 sources · Grade B
Zinc: cold duration, lozenge dosing and copper balance
Lozenges started early may shorten colds, but the newest Cochrane review rates the evidence low certainty. Long-term high doses can deplete copper.
6 min · 5 sources · Grade C
NAC (N-acetylcysteine)
A glutathione precursor with one notable flu-season trial and stronger data in chronic lung disease, which is a drug use, not a supplement claim.
4 min · 2 sources · Grade C
Vitamin C and colds
Does not prevent colds in most people. Regular use slightly shortens them. People under heavy physical stress are the exception.
4 min · 2 sources · Grade C
Elderberry: honestly graded
Small trials, mixed results, low certainty. Not enough to recommend.
3 min · 3 sources · Grade D
Probiotics and upper respiratory infections
Cochrane finds fewer infections with low-certainty evidence. Effects are strain-specific and products vary.
4 min · 2 sources · Grade C