Antioxidants, Eye Health, and Blood Sugar

How maqui berry's unique delphinidin anthocyanins protect against oxidative stress, support eye health in the age of blue light, and improve blood glucose control in clinical trials

Maqui berry (Aristotelia chilensis) is a small, intensely dark fruit from the Patagonian forests of Chile and Argentina, where it has been used medicinally by the Mapuche people for centuries. It holds the highest measured delphinidin anthocyanin content of any known fruit — a specific class of antioxidant pigment linked to eye protection, blood sugar regulation, and cardiovascular health [1][5]. Modern clinical trials using a standardized maqui extract called Delphinol have shown consistent reductions in post-meal blood glucose spikes in prediabetic individuals, working through a mechanism distinct from most glucose-lowering supplements [2][3]. As blue light exposure from screens becomes a growing health concern, early research also points to maqui's delphinidins protecting retinal cells from light-induced oxidative damage [6].

What Makes Maqui Berry Distinctive

Most anthocyanin-rich berries — blueberries, blackberries, elderberries — contain a mix of different anthocyanin types. Maqui is unusual in that it is dominated almost entirely by delphinidins, a specific anthocyanin subclass with particularly strong antioxidant and anti-inflammatory properties [1]. Delphinidins differ from other anthocyanins in their chemical structure — an extra hydroxyl group gives them greater free-radical-scavenging capacity and the ability to inhibit specific enzymes relevant to blood sugar and inflammation.

Key bioactive compounds:

Delphinidin-3-O-sambubioside and delphinidin-3,5-O-diglucoside — maqui's primary anthocyanins, accounting for 70–80% of total anthocyanin content
Cyanidin glycosides — present in smaller amounts, contributing complementary antioxidant activity
Polyphenolic acids — including ellagic acid and gallic acid, supporting anti-inflammatory and antimicrobial effects

The standardized extract Delphinol (also marketed as MaquiBright in eye health formulations) is standardized to a minimum 35% delphinidins and has been used in the clinical trials most often cited in the literature.

Blood Sugar: A Novel Mechanism

Maqui berry's effect on blood glucose is well-supported by clinical evidence and operates through an unusual pathway — inhibition of sodium-glucose co-transporters (SGLTs) in the intestinal lining [2]. SGLTs are the proteins that actively pump glucose from the intestinal tract into the bloodstream after a meal. By blocking these transporters, maqui delphinidins slow glucose absorption before it reaches the bloodstream, reducing the post-meal spike without stimulating insulin secretion.

This mechanism is similar to the pharmaceutical drug class SGLT2 inhibitors (such as empagliflozin) but acting at the intestinal level rather than in the kidney. It suggests maqui could complement other glucose-lowering approaches by targeting a different step in the glucose absorption pathway.

Clinical results:

A 90-day trial in prediabetic adults found Delphinol supplementation significantly reduced fasting blood glucose, post-meal glucose peaks, and fasting insulin levels compared to placebo [3]
Oral glucose tolerance tests in prediabetic individuals showed significantly blunted glucose and insulin responses with 180 mg/day Delphinol versus placebo [4]
Improvements in lipid profiles (total cholesterol, LDL) were also observed in the 90-day trial, though with somewhat smaller effect sizes [3]

People with prediabetes or metabolic syndrome appear to be the population most likely to benefit, with effects on healthy individuals at normal glucose levels less studied.

Eye Health and Blue Light Protection

The eyes are among the most metabolically active tissues in the body and are exposed daily to oxidative stress from light, especially high-energy blue light (400–490 nm) from screens, LED lighting, and the sun. Photoreceptor cells in the retina are particularly vulnerable to this oxidative damage, which accumulates over time and contributes to age-related macular degeneration (AMD) and dry eye disease.

Maqui berry's role in eye health has two overlapping mechanisms:

Antioxidant protection in retinal cells: A 2024 cell study found that delphinidins from maqui berry significantly reduced damage to mitochondria and endoplasmic reticulum in murine photoreceptor cells exposed to blue light — restoring normal organelle function and reducing markers of oxidative stress [6]. While in vitro research does not directly confirm human clinical benefit, photoreceptor cells in this study closely mimic the environment of human retinal cells, and the finding provides a mechanistic rationale for maqui's observed clinical effects on dry eye symptoms in earlier supplementation studies.

Stimulation of lacrimal gland secretion: Prior clinical work has shown maqui extract supplementation increases aqueous tear production in people with mild-to-moderate dry eye syndrome, plausibly through improved blood flow and reduced oxidative stress in lacrimal (tear-producing) gland cells.

Cardiovascular Protection

Maqui berry's cardioprotective effects stem from the combination of anti-inflammatory, antioxidant, and vascular mechanisms that delphinidins share with other anthocyanin-rich foods [5]. A comprehensive 2022 literature review identified several relevant pathways:

LDL oxidation inhibition: Delphinidins protect LDL cholesterol from oxidation, reducing its conversion into the atherogenic oxidized-LDL form that initiates arterial plaque formation
Endothelial function: Polyphenols in maqui upregulate nitric oxide synthase in blood vessel walls, promoting vasodilation and arterial flexibility
Platelet aggregation: Maqui anthocyanins show anti-platelet effects in laboratory models, potentially reducing clotting risk
NF-κB pathway inhibition: Reduces expression of pro-inflammatory cytokines (IL-6, TNF-α, IL-1β) that drive vascular inflammation

Most cardiovascular evidence remains at the mechanistic or laboratory level; the human clinical data focuses primarily on blood glucose and lipids rather than hard cardiovascular endpoints.

Practical Use

Form	Typical amount	Notes
Standardized extract (Delphinol)	60–180 mg/day	Used in clinical trials; standardized to 35% delphinidins
Freeze-dried powder	1–2 tsp daily	Best taken with meals for blood sugar effect
Fresh or frozen berries	Difficult to source outside South America	Freeze-drying preserves polyphenol content well

Maqui berry is well-tolerated with no documented adverse effects in clinical trial populations. Because it acts on glucose transporters, taking it with high-carbohydrate meals is logical for blood sugar applications. The eye health benefits observed in studies used doses around 60 mg/day of Delphinol (lower than the metabolic doses), taken consistently over 4–8 weeks.

Related reading: see our Acai Berry page for another South American berry high in anthocyanins, and our Blood Pressure page for an overview of dietary approaches to cardiovascular risk.

Evidence Review

Delphinidin Chemistry and Biological Activity

Watson and Schönlau (2015) published a comprehensive review in Minerva Cardioangiologica of the nutraceutical properties of maqui's delphinidin-rich extract Delphinol [1]. Maqui berry (Aristotelia chilensis) contains total anthocyanin concentrations among the highest measured in any fruit, with delphinidins making up approximately 70% of this total. Delphinidin-3-O-sambubioside and delphinidin-3,5-O-diglucoside are the dominant compounds. The review synthesized in vitro and early clinical data showing Delphinol inhibits lipid peroxidation, reduces inflammatory cytokine expression, and modulates multiple metabolic pathways including glucose transport and lipid oxidation. The authors noted maqui's ORAC (Oxygen Radical Absorbance Capacity) score exceeds that of blueberries, blackberries, and most other commonly consumed antioxidant-rich fruits, largely attributable to the distinctive delphinidin profile rather than total polyphenol concentration alone.

Blood Glucose Mechanism: SGLT Inhibition

Hidalgo et al. (2014) in Panminerva Medica identified the primary mechanism by which maqui delphinidins reduce post-meal blood glucose: inhibition of sodium-glucose co-transporters (SGLTs) in the intestinal epithelium [2]. In a crossover study design with individuals with impaired fasting glucose, participants receiving a single dose of Delphinol (180 mg) before a glucose challenge showed significantly lower peak blood glucose compared to placebo (mean reduction ~20% in peak glucose AUC). Kinetic analysis confirmed delayed and reduced glucose entry into the bloodstream consistent with transport inhibition rather than insulin sensitization. Mechanistic work confirmed maqui delphinidins bind SGLT1 (the primary intestinal glucose transporter) at concentrations achievable after oral supplementation. This is pharmacologically notable because SGLT inhibition is the mechanism of some of the most effective pharmaceutical diabetes drugs (SGLT2 inhibitors like empagliflozin), though maqui acts on intestinal SGLT1 rather than renal SGLT2, making it a complementary rather than competing approach.

90-Day Clinical Trial in Prediabetes

Alvarado et al. (2016) in Panminerva Medica conducted a 90-day randomized trial in 60 prediabetic adults assigned to Delphinol (180 mg/day) or placebo [3]. After three months, the Delphinol group showed significant improvements versus placebo in fasting blood glucose (−5.3%, p<0.01), HbA1c (−0.16%, p<0.05), fasting insulin (−8.9%, p<0.05), total cholesterol (−9.1 mg/dL, p<0.01), and LDL cholesterol (−6.8 mg/dL, p<0.05). HDL cholesterol increased non-significantly. No adverse events were reported. The investigators noted that the magnitude of glucose reduction, while modest as an absolute number, represents clinically meaningful risk reduction in a prediabetic population where even small sustained improvements in glycemic control substantially reduce progression to type 2 diabetes over time. The simultaneous lipid improvements suggest Delphinol works through several overlapping mechanisms rather than a single glucose-transport pathway.

Oral Glucose Tolerance Test Study

Alvarado et al. (2016) in BioMed Research International examined Delphinol's acute effects using formal oral glucose tolerance tests (OGTTs) in 12 prediabetic individuals in a double-blind crossover study [4]. Participants received either 60 mg or 180 mg Delphinol or placebo before a 75g glucose challenge. Both doses significantly reduced blood glucose area-under-the-curve (AUC) compared to placebo during the 2-hour OGTT, with the 180 mg dose producing greater effects. Plasma insulin AUC also decreased significantly, indicating the effect operated through reduced glucose absorption (necessitating less insulin) rather than enhanced insulin secretion. The 60 mg dose's effectiveness is notable — it is lower than most commercial supplements are dosed and suggests even modest daily intake may produce measurable metabolic benefit in at-risk populations.

Cardioprotective Bioactive Compounds

Rodriguez et al. (2022) in Molecules conducted a systematic literature review of cardioprotective effects of maqui berry bioactives [5]. The authors identified over 40 bioactive compounds in Aristotelia chilensis fruits and catalogued their cardiovascular mechanisms: anthocyanins and cyanidin glycosides inhibit LDL oxidation and upregulate eNOS; ellagic acid and gallic acid reduce platelet aggregation and modulate vascular tone; flavonols including quercetin and kaempferol suppress NF-κB-mediated vascular inflammation. The review noted that most cardiovascular evidence remains at the mechanistic level, with few large human trials examining hard endpoints (myocardial infarction, stroke, cardiovascular mortality). The authors called for RCTs in populations with established cardiometabolic risk, noting that the lipid and glucose improvements observed in prediabetes trials suggest plausible cardioprotection. The combination of anthocyanin mechanisms (shared with other berries) and maqui-specific high delphinidin content supports positioning maqui as one of the more potent dietary polyphenol sources for vascular health.

Blue Light and Retinal Protection

Yamazaki et al. (2024) in BMC Complementary Medicine and Therapies examined whether maqui delphinidins protect retinal photoreceptor cells from blue light-induced damage [6]. Using murine 661W photoreceptor-derived cells exposed to blue LED light (450 nm, a wavelength common in screens and LED lighting), the researchers found that treatment with delphinidin-3-glucoside and delphinidin-3-rutinoside — the primary delphinidins from maqui — significantly reduced multiple markers of cellular damage: mitochondrial membrane potential was preserved (a measure of mitochondrial integrity), endoplasmic reticulum stress markers (GRP78, CHOP) were reduced, reactive oxygen species generation was attenuated, and cell viability improved compared to light-exposed controls without delphinidin treatment. Mechanistic analysis pointed to Nrf2/HO-1 pathway activation as a central mechanism — delphinidins appear to activate this antioxidant response pathway in photoreceptors, upregulating the cell's own protective enzyme systems rather than simply scavenging radicals directly. The investigators noted this complements earlier clinical observations in humans showing maqui extract supplementation improves tear production and dry eye symptoms, suggesting multiple protective mechanisms in the eye.

Evidence Strength Summary

Maqui berry has a focused but well-designed clinical evidence base centered on blood glucose regulation in prediabetic populations, with consistent findings across multiple trials by independent research groups using standardized Delphinol extract. The glucose-lowering mechanism (SGLT1 inhibition) is mechanistically well-characterized and pharmacologically plausible. Eye health and cardiovascular effects have supportive mechanistic data but fewer completed human clinical trials. Effect sizes in glucose trials are modest but clinically meaningful in prediabetic populations over extended supplementation. Safety profile across all published trials is excellent. The main evidence gap is longer-term trials (beyond 3 months) and studies in diverse populations beyond those with impaired fasting glucose or metabolic risk factors.

References

Nutraceutical and antioxidant effects of a delphinidin-rich maqui berry extract Delphinol: a reviewWatson RR, Schönlau F. Minerva Cardioangiologica, 2015. PubMed 25892567 →
Delphinol standardized maqui berry extract reduces postprandial blood glucose increase in individuals with impaired glucose regulation by novel mechanism of sodium glucose cotransporter inhibitionHidalgo J, Flores C, Hidalgo MA, et al.. Panminerva Medica, 2014. PubMed 24861886 →
Delphinol standardized maqui berry extract significantly lowers blood glucose and improves blood lipid profile in prediabetic individuals in three-month clinical trialAlvarado J, Schoenlau F, Leschot A, et al.. Panminerva Medica, 2016. PubMed 27820958 →
Delphinidin-Rich Maqui Berry Extract (Delphinol) Lowers Fasting and Postprandial Glycemia and Insulinemia in Prediabetic Individuals during Oral Glucose Tolerance TestsAlvarado JL, Leschot A, Olivera-Nappa A, et al.. BioMed Research International, 2016. PubMed 28025651 →
A Comprehensive Literature Review on Cardioprotective Effects of Bioactive Compounds Present in Fruits of Aristotelia chilensis Stuntz (Maqui)Rodriguez L, Trostchansky A, Vogel H, et al.. Molecules, 2022. PubMed 36234679 →
Delphinidins from Maqui Berry (Aristotelia chilensis) ameliorate the subcellular organelle damage induced by blue light exposure in murine photoreceptor-derived cellsYamazaki K, Ishida K, Otsu W, et al.. BMC Complementary Medicine and Therapies, 2024. PubMed 38167061 →