Cyanidin

Pharmacology & Research

Cyanidin is the aglycone — the sugar-free core — of the most common anthocyanin pigments that colour red, purple and blue fruits and flowers. The single most important thing to know is that the free aglycone is largely a paper entity in the body: in plants cyanidin occurs almost entirely as glycosides, chiefly cyanidin-3-glucoside (C3G), and the free molecule is chemically unstable at physiological pH (its coloured flavylium cation converts to colourless carbinol and chalcone forms). So almost every human “cyanidin” finding is really about C3G or an anthocyanin mixture (berry/bilberry extract), and much of the apparent activity is actually its downstream metabolite protocatechuic acid ^{5Reference 5Vitaglione P et al. · 2007Protocatechuic acid is the major human metabolite of cyanidin-glucosidesView study →}. The aglycone’s own best-supported property is direct antioxidant radical scavenging — where aglycones out-perform their glycosides ^{1Reference 1Kähkönen MP · 2003Antioxidant activity of anthocyanins and their aglyconsView study →} — and one of the few studies to test the aglycone directly showed it suppresses inducible nitric-oxide synthase in human coronary smooth-muscle cells ^{2Reference 2Xia N et al. · 2014Artichoke, cynarin and cyanidin downregulate the expression of inducible nitric-oxide synthase in human coronary smooth-muscle cellsView study →}.

1. Antioxidant (property)

Cyanidin’s catechol (ortho-dihydroxy) B-ring makes it a strong hydrogen-atom and electron donor, and antioxidant activity decreases as sugars are added — so the free aglycone out-scavenges its own glycosides ^{1Reference 1Kähkönen MP · 2003Antioxidant activity of anthocyanins and their aglyconsView study →}. It is the pigment behind the strong radical-scavenging capacity of cyanidin-rich material such as red hibiscus petals (~36 mg/g fresh) ^{11Reference 11Mejía-Terán A et al. · 2023Colour, antioxidant capacity and flavonoid composition in Hibiscus rosa-sinensis cultivarsView study →}. This is the most aglycone-specific property it has.

Gap: these are cell-free/chemical assays; no antioxidant benefit has been shown in humans for the isolated aglycone, and the unstable molecule barely reaches tissues intact (see Pharmacokinetics) ^{1,3Reference 1Kähkönen MP · 2003Antioxidant activity of anthocyanins and their aglyconsView study →Reference 3Czank C et al. · 2013Human metabolism and elimination of the anthocyanin cyanidin-3-glucoside: a ¹³C-tracer studyView study →}.

2. Anti-inflammatory

In one of the few studies to test the aglycone directly, cyanidin downregulated inducible nitric-oxide synthase (iNOS) in human coronary smooth-muscle cells ^{2Reference 2Xia N et al. · 2014Artichoke, cynarin and cyanidin downregulate the expression of inducible nitric-oxide synthase in human coronary smooth-muscle cellsView study →}, consistent with the broader anthocyanin theme of NF-κB-pathway suppression.

Gap: a single cell model for the aglycone; most anti-inflammatory anthocyanin data are mixtures or C3G, and there is no human anti-inflammatory data for the isolated molecule ^{2Reference 2Xia N et al. · 2014Artichoke, cynarin and cyanidin downregulate the expression of inducible nitric-oxide synthase in human coronary smooth-muscle cellsView study →}.

3. Vascular / endothelial

The iNOS downregulation in coronary smooth muscle gives a vascular-protective rationale ^{2Reference 2Xia N et al. · 2014Artichoke, cynarin and cyanidin downregulate the expression of inducible nitric-oxide synthase in human coronary smooth-muscle cellsView study →}, and human cardiovascular signals exist — but only for anthocyanin/berry mixtures and C3G.

Gap: there are no isolated-cyanidin human vascular endpoints; this is mechanism-level only ^{2Reference 2Xia N et al. · 2014Artichoke, cynarin and cyanidin downregulate the expression of inducible nitric-oxide synthase in human coronary smooth-muscle cellsView study →}.

4. Metabolic / anti-obesity

The most-cited “cyanidin” metabolic story — brown-adipose programming, reduced white fat, Nrf2/AMPK engagement — is for the glycoside C3G, reviewed extensively ^{7,8Reference 7Guo H et al. · 2024Recent advances on cyanidin-3-O-glucoside in preventing obesity-related metabolic disordersView study →Reference 82023ReviewA review of the role of the anthocyanin cyanidin-3-O-β-glucoside in obesity-related complicationsView study →}.

Gap: C3G is a separate molecule (its own entry, pending build); the free aglycone is not the studied agent, and even the C3G human evidence is thin and uses berry/anthocyanin mixtures ^{7,8Reference 7Guo H et al. · 2024Recent advances on cyanidin-3-O-glucoside in preventing obesity-related metabolic disordersView study →Reference 82023ReviewA review of the role of the anthocyanin cyanidin-3-O-β-glucoside in obesity-related complicationsView study →}.

5. Anticancer

Anthocyanins and anthocyanin-rich extracts show anti-carcinogenic activity in cell culture and animal tumour models, as summarised in a cancer-prevention review that itself notes poor translation to human epidemiology ^{6Reference 6Wang LS · 2008Anthocyanins and their role in cancer preventionView study →}.

Gap: mixtures/extracts, not the isolated aglycone, with no confirmed human efficacy ^{6Reference 6Wang LS · 2008Anthocyanins and their role in cancer preventionView study →}.

6. Vision / eye (mixture lore)

Bilberry anthocyanoside supplements are traditionally promoted for night vision, and a retinal-inflammation model showed vision preservation by anthocyanin-rich bilberry extract ^{9Reference 9Matsumoto H et al. · 2012Vision preservation during retinal inflammation by anthocyanin-rich bilberry extractView study →}. But a systematic review of placebo-controlled trials found no robust evidence for a night-vision benefit in healthy people ^{10Reference 10Canter PH · 2004Systematic reviewAnthocyanosides of Vaccinium myrtillus (bilberry) for night vision — a systematic review of placebo-controlled trialsView study →}.

Gap: entirely bilberry/anthocyanin mixture, not cyanidin aglycone, and negative on robust RCT — treat as lore ^{9,10Reference 9Matsumoto H et al. · 2012Vision preservation during retinal inflammation by anthocyanin-rich bilberry extractView study →Reference 10Canter PH · 2004Systematic reviewAnthocyanosides of Vaccinium myrtillus (bilberry) for night vision — a systematic review of placebo-controlled trialsView study →}.

Mechanisms

Target / pathway	Effect	Relevant to
Catechol B-ring H-atom/electron donation	direct radical scavenging; aglycone > glycosides	antioxidant
Inducible NOS (iNOS) expression	downregulated in human coronary smooth-muscle cells (aglycone)	anti-inflammatory, vascular
NF-κB signalling	suppression → lower pro-inflammatory mediators (class/C3G)	anti-inflammatory
Nrf2 / AMPK (C3G, not aglycone)	↑ antioxidant enzymes, brown-fat programming	metabolic — attribute to C3G

Pharmacokinetics

This is the central caveat. Anthocyanins and anthocyanidins are notoriously poorly bioavailable: in the definitive ¹³C-labelled human tracer study of C3G (500 mg oral), relative bioavailability was ~12% with only trace parent in serum, most of the label appearing as downstream metabolites ^{3Reference 3Czank C et al. · 2013Human metabolism and elimination of the anthocyanin cyanidin-3-glucoside: a ¹³C-tracer studyView study →}, and human PK work confirms intact anthocyanins circulate at nanomolar levels while phenolic-acid metabolites dominate exposure ^{4Reference 4de Ferrars RM et al. · 2014The pharmacokinetics of anthocyanins and their metabolites in humansView study →}. The free aglycone is chemically unstable at neutral pH — the flavylium cation opens to colourless carbinol/chalcone forms — so cyanidin barely exists as such in plasma; it is a transient breakdown/deglycosylation species. Its major human metabolite is protocatechuic acid, which accounted for ~73% of ingested cyanidin-glucosides in one study, with serum protocatechuic acid (~490 nmol/L) vastly exceeding intact C3G (~2 nmol/L) ^{5Reference 5Vitaglione P et al. · 2007Protocatechuic acid is the major human metabolite of cyanidin-glucosidesView study →}. Much of the bioactivity attributed to “cyanidin” may in fact be that of protocatechuic acid and other phenolic acids.

Clinical trials

There are essentially no trials of the isolated cyanidin aglycone — its instability makes that impractical. Human data labelled “cyanidin” are either C3G pharmacokinetic/metabolic studies ^{3,4,5Reference 3Czank C et al. · 2013Human metabolism and elimination of the anthocyanin cyanidin-3-glucoside: a ¹³C-tracer studyView study →Reference 4de Ferrars RM et al. · 2014The pharmacokinetics of anthocyanins and their metabolites in humansView study →Reference 5Vitaglione P et al. · 2007Protocatechuic acid is the major human metabolite of cyanidin-glucosidesView study →} or anthocyanin/berry/bilberry mixture trials ^{6,10Reference 6Wang LS · 2008Anthocyanins and their role in cancer preventionView study →Reference 10Canter PH · 2004Systematic reviewAnthocyanosides of Vaccinium myrtillus (bilberry) for night vision — a systematic review of placebo-controlled trialsView study →}; the vision claims specifically fail robust RCT support ^{10Reference 10Canter PH · 2004Systematic reviewAnthocyanosides of Vaccinium myrtillus (bilberry) for night vision — a systematic review of placebo-controlled trialsView study →}. Attribute all human evidence to C3G or mixtures, never the aglycone.

Last checked: July 2026.

Toxicity & Safety

Cyanidin and its glycosides are ubiquitous dietary pigments eaten in coloured fruits, vegetables and flowers, and are regarded as safe at ordinary dietary levels with no significant toxicity from normal food intake. Anthocyanin and berry supplements are well tolerated in trials at doses well above dietary intake. There are no established drug interactions for the isolated aglycone; theoretical additive antioxidant, anti-inflammatory or mild antiplatelet effects from anthocyanin-rich intake are unconfirmed, and the poor systemic bioavailability further limits any systemic-toxicity concern.

Dosage

There is no established dose for isolated cyanidin — it is not used as a standalone supplement and is unstable. For research context only (glycoside/mixture figures, not aglycone dosing, and not a recommendation): the human ¹³C tracer study used a 500 mg oral bolus of C3G ^{3Reference 3Czank C et al. · 2013Human metabolism and elimination of the anthocyanin cyanidin-3-glucoside: a ¹³C-tracer studyView study →}; anthocyanin/bilberry supplement trials commonly use extracts up to ~320–720 mg/day ^{10Reference 10Canter PH · 2004Systematic reviewAnthocyanosides of Vaccinium myrtillus (bilberry) for night vision — a systematic review of placebo-controlled trialsView study →}; and typical Western dietary anthocyanin intake is on the order of ~200 mg/day ^{6Reference 6Wang LS · 2008Anthocyanins and their role in cancer preventionView study →}.

References