The evidence picture is weaker under the current grading system than the old percentage-based grades implied. General immune-function evidence now leads the page, while cold-duration, deficiency-correction, skin, fertility, and wound-healing claims look mixed rather than clearly established. The popular "immune booster" framing remains more nuanced than marketing suggests.
Each row is a different health effect. A means the support looks strongest, B likely helpful, C mixed or modest, and — not enough human evidence yet.
Papers are individual studies. Research reviews summarize evidence from multiple studies, such as systematic reviews and meta-analyses.
Dose, form and timing based on trials in the database.
Products that pass third-party quality testing.
Product quality data coming soon
Product recommendations are being built from USP Verified, NSF Certified, and Labdoor test data. Products will only appear here after the supplement itself clears the evidence bar above — and only if the product passes third-party purity testing.
Grades come from 175 unique research papers indexed from PubMed — including 44 meta-analyses, 38 systematic reviews, 43 Cochrane reviews, and 44 randomized trials. The "general immunity" health effect graded D because only one medium-confidence review passed the quality filter — most reviews mix very different sub-outcomes (inflammation, vaccines, malaria, COVID) that don't cleanly synthesize. Trials using multi-ingredient eye formulas were excluded because zinc's individual contribution cannot be isolated. Each supplement is graded by health effect using a certainty × effect matrix applied across PubMed evidence per health effect. Cochrane reviews and high-quality systematic reviews carry the most weight. From abstract-only data, "high certainty" is rare — most A grades come from moderate certainty plus consistent meaningful-positive evidence. See Methodology for full detail.
Read the full methodology → · Download all 175 citations (PDF)