Phlorizin

Phlorizin (Phloridzin): A Comprehensive Reference

1. Identity and Chemical Characterization

1.1 Names and Nomenclature

The phenolic compound phlorizin (also rendered as phloridzin, phlorrhizin, phlorhizin, or phlorizoside) is a prominent member of the chemical class of dihydrochalcones, which are phenylpropanoids. Its systematic chemical name is phloretin 2′-O-β-d-glucopyranoside. Phlorizin belongs to the class of organic compounds known as flavonoid O-glycosides. More precisely, phlorizin (phloretin-2′-O-β-glucopyranoside) is an O-glucoside of phloretin, a member of the dihydrochalcone family that is, in turn, a subclass of flavonoids.

Phlorizin is a naturally occurring dihydrochalcone flavonoid glucoside, chemically known as phloretin 2′-O-β-d-glucopyranoside, with the molecular formula C₂₁H₂₄O₁₀ and a molecular weight of 436.41 g/mol. Phloridzin belongs to the chemical class of dihydrochalcones, phenylpropanoids with structures closely related to those of the immediate flavonoid precursors, the chalcones. It consists of a C6–C3–C6 skeleton structure (two aromatic rings connected by a C3 chain) with a β-d-glucopyranose moiety attached at position 2′.

1.2 Physical Properties

It appears as a white to pale yellow crystalline powder with a sweet taste, melting point around 113–114 °C, and limited solubility in water but good solubility in DMSO and ethanol. It is poorly soluble in ether and cold water, but soluble in ethanol and hot water. Upon prolonged exposure to aqueous solutions, phlorizin hydrolyzes to phloretin and glucose.

1.3 Biosynthesis

The biosynthesis of phloridzin was investigated only recently with recombinant enzymes and plant protein extracts and involved a NADPH-dependent dehydrogenase, chalcone synthase, and UDP-glucose:phloretin 2′-O-glycosyltransferase.

2. Natural Sources and Distribution

2.1 Primary Botanical Source

The apple tree (Malus sp.) accumulates high amounts of phloridzin, whereas few other species contain this compound only in low amounts. Phlorizin is found primarily in unripe Malus (apple) root bark, and trace amounts have been found in strawberry. In Malus, it is most abundant in vegetative tissues (such as leaves and bark) and seeds. Phloridzin mainly exists in root barks, stems, leaflets, and fruit of the apple tree.

Additionally, Malus sp. shows a species- and tissue-specific distribution of phloridzin and its derivatives. Phlorizin is primarily accumulated in the roots, bark, leaves, and immature fruits of Rosaceae plants, particularly apples, where it constitutes up to 5–14% of dry weight in leaves, serving as a phytoalexin against pathogens.

2.2 Other Plant Sources

Aside from apple trees, the occurrence of phloridzin was described in about thirty plant species, including Fragaria × ananassa (Rosaceae), Fagopyrum esculentum (Polygonaceae), and Vaccinium macrocarpon (Ericaceae). However, in species other than M. domestica, only exceptionally low amounts of phloridzin were detected. Closely related species such as pear (Pyrus communis), cherry, and other fruit trees in the Rosaceae do not contain phlorizin at meaningful concentrations.

An important alternative botanical source was identified in a Chinese medicinal plant. The tender leaves of Lithocarpus polystachyus Rehd., called Sweet Tea (ST) in southern China, have been commonly used as a sweet tonic beverage and traditional herb, taken for hundreds of years without evidence of adverse effects or toxicity. During research seeking sweet compounds in the tender leaves, abundant phloridzin was found, at amounts of up to around 7%, and thus ST was found to be a potentially new substitute for the root bark of apple trees as a rich and cheaper source for phloridzin production.

2.3 Dietary Exposure

On average, European people consume 0.7–7.5 mg/d phloridzin, the main contributors being apples and apple juice. High-level consumers may get up to 52 mg/d of phloridzin. Phlorizin may be considered a normal constituent of the human diet, and is partly responsible for the colour and flavour of apple juice and cider. In natural sources, it may occur alongside other polyphenols such as quercetin, catechin, epicatechin, procyanidins, and rutin.

3. History and Traditional Use

3.1 Isolation and Early Investigation (19th Century)

Phlorizin was extracted from the bark of the apple tree in 1835 as part of the quest for active drugs in tree bark, previous examples being the salicylates and quinine. De Koninck (1835) isolated and described a bitter-tasting substance with antipyretic effects from the bark of the apple tree. He found that this new compound was more prevalent in root bark than in stem bark and suggested calling it phloridzin (from the Greek phloiós, meaning "bark," and rhíza, meaning "root").

Phloridzin was previously considered a candidate for the treatment of fever, infectious diseases, and malaria. It was actively investigated as a potential antimalarial. This early interest paralleled the medical context of the era, in which tree-bark compounds such as quinine (from cinchona bark) were being pursued systematically for their antipyretic and antiparasitic properties.

3.2 Discovery of Glycosuric Properties (Late 19th Century)

In 1886, von Mering showed that the drug produced glycosuria, polyuria, and weight loss in dogs, thus imitating diabetes. Von Mering demonstrated that doses greater than 1 gram daily produced glycosuria, and showed that the drug produced glycosuria, polyuria, and weight loss in dogs, thus imitating diabetes. Although intensively investigated at the time, its mode of action remained mysterious until the elucidation of sodium/glucose cotransporter mechanisms in the 1960s.

3.3 Early 20th-Century Research

Its ability to lower glucose in animals was first recognised in 1903 and confirmed in humans in 1933 (Chasis et al, 1933). By the early 1950s, it was known that phlorizin blocked facilitated transport of glucose into erythrocytes and inhibited glucose transport in both the kidney and the small intestine, but it was not until after the sodium-glucose co-transporter-2 (SGLT2) was fully characterised in the early 1990s that the mechanisms and potential significance of phlorizin-induced renal glycosuria attracted real interest.

3.4 Traditional Use in Chinese Herbal Medicine

As noted above, Lithocarpus polystachyus leaves (Sweet Tea), a phloridzin-rich plant, have been commonly used as a sweet tonic beverage and traditional herb in southern China, taken for hundreds of years without evidence of adverse effects or toxicity. This represents the most thoroughly documented traditional-use context for phloridzin as a dietary constituent outside the apple-tree framework.

3.5 Use as a Physiological Research Tool

The dihydrochalcone phlorizin is a natural product and dietary constituent found in a number of fruit trees. It has been used as a pharmaceutical and tool for physiology research for over 150 years. With the characterization of renal glucose reabsorption in the proximal tubule in the 1960s, the cloning of the SGLT2 cotransporter in the 1990s, and further understanding of renal handling of glucose and the pharmacological effects of phlorizin, inhibition of renal glucose reabsorption was studied as a target for diabetes control.

4. Key Constituents and Active Compounds

4.1 Phlorizin as the Primary Active Compound

The presence of the glucose moiety in the structure of phlorizin is an important structural feature for the observed antidiabetic properties, as its aglycone, phloretin, is by order of magnitude less potent than phlorizin at SGLT inhibition. Nevertheless, because phlorizin is hydrolyzed in the gut to phloretin, both parent and metabolite contribute to biological activity in vivo.

4.2 Phloretin (Primary Metabolite / Aglycone)

Phloretin, a metabolite of phlorizin, is a known uncoupler and inhibitor of mitochondrial oxidative phosphorylation. Phloretin inhibits GLUT1, which is widely found in numerous organs and tissues, and has been demonstrated to abruptly decrease brain glucose levels following intravenous administration. The hydrolysis of phlorizin in the small intestine suggests that at least some of the numerous biological activities reported for phlorizin are mediated through its metabolic product, phloretin.

4.3 Co-occurring Polyphenols in Apple Sources

When phlorizin is consumed via apple-based foods, it co-occurs with other bioactive polyphenols. In natural sources, it may occur with other polyphenols such as quercetin, catechin, epicatechin, procyanidins, and rutin, and synergistic or additive effects among these constituents have been proposed but not definitively characterized in human studies.

5. Mechanisms of Action

5.1 SGLT1 and SGLT2 Inhibition (Primary Mechanism)

Phlorizin is an inhibitor of SGLT1 and SGLT2 because it competes with d-glucose for binding to the carrier; this action reduces renal glucose transport, lowering the amount of glucose in the blood. Phlorizin contains a glucose moiety which binds to SGLT1 and SGLT2 with 2,000–3,000 times the affinity of glucose itself. SGLT1 is a high-affinity, low-capacity transporter abundant in the small intestine, with some expression in the kidney as well. SGLT2 is a low-affinity, high-capacity transporter in the kidney that accounts for approximately 90% of glucose reabsorption into the blood stream.

The sodium glucose cotransporter SGLT1, expressed mainly in the intestine and kidney, has been explored extensively for understanding the mechanism of sugar cotransport and its inhibition by phlorizin. It has been shown that inhibition of SGLT1 by phlorizin involves its interaction followed by major conformational changes in the phlorizin binding domain (PBD) in C-terminal loop 13.

Phlorizin's main action is to produce renal glycosuria and block intestinal glucose absorption through inhibition of the sodium glucose transporters located in the proximal renal tubule and mucosa of the small intestine.

5.2 Antioxidant Mechanisms

Studies have shown that phlorizin can increase the activity of antioxidant enzymes in the body, such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione peptide peroxidase (GPx), and glutathione reductase (GR). Phlorizin can exert antioxidant effects by regulating the IL-1β/IKB-α/NF-κB signaling pathway.

Comparatively, the DPPH assay results showed that phloretin (12.95 mg AAE/L) had a 3.7-fold higher free-radical scavenging activity than phlorizin (3.52 mg AAE/L), suggesting that the aglycone form is a more potent direct antioxidant, whereas phlorizin may confer antioxidant benefits partly through enzymatic upregulation.

5.3 Anti-inflammatory Mechanisms

Phlorizin can exert antioxidant and anti-inflammatory effects by regulating the IL-1β/IKB-α/NF-κB signaling pathway. In preclinical models, research by Cambeiro-Pérez et al. (2021) explored its immunomodulatory activities on human THP-1 macrophages, revealing that phlorizin alters metabolic pathways to reduce inflammation.

5.4 Anticancer Mechanisms

Key anticancer mechanisms include glucose transporter inhibition (GLUT1/2), modulation of PI3K/AKT/mTOR and JAK2/STAT3 signaling, and suppression of metastasis and angiogenesis. Phlorizin also inhibits the progression of cancer cells' proliferation by the JAK2/STAT3 pathway.

5.5 Gut Microbiota Modulation

Research using an in vitro fermentation model showed that phlorizin (PHZ) treatment significantly increased the phylum Bacteroidota and transiently reduced Firmicutes at 6 h. In vivo mouse studies found that PHZ supplementation significantly reduced HFD-induced body weight gain, alleviated metabolic disorders like insulin resistance and elevation of serum lipopolysaccharides (LPS), attenuated HFD-induced gut microbiota alterations, enhanced short-chain fatty acids (SCFAs) production, and inhibited fecal LPS production.

5.6 Neuroprotective Mechanisms

In Alzheimer's disease mouse models, gavage administration of phlorizin for 8 weeks improved cognitive dysfunction and lipid disorders in APP/PS1 mice. In astrocytes induced by palmitic-acid-mediated lipid metabolic disorder, phlorizin treatment improved astrocytic lipid accumulation by upregulating PPARα and its downstream pathways, thereby promoting astrocytic fatty acid oxidation.

6. Bioavailability and Pharmacokinetics

6.1 The Oral Bioavailability Problem

The therapeutic potential of phlorizin is limited by poor oral bioavailability because of its tendency to be hydrolysed in the gut to its aglycone, phloretin. Phlorizin is easily hydrolyzed by lactase-phlorizin hydrolase and poorly absorbed in the intestine, making it a difficult drug to develop for the treatment of diabetes. Pharmacokinetically, it is quickly metabolised by lactase-phlorizin hydrolase, and poorly absorbed by the small intestine, resulting in poor bioavailability.

Phlorizin has no oral bioavailability in the pharmacological sense, meaning that essentially none reaches the systemic circulation intact after oral ingestion; when orally consumed, phlorizin is nearly entirely converted into phloretin by hydrolytic enzymes in the small intestine.

6.2 Metabolic Pathway

Phlorizin (PHZ) is converted into phloretin (PHT) through an enzyme-catalyzed hydrolysis reaction, and PHT is further transformed into conjugates with glycose after both oral and intravenous administrations. Like other flavonoids, the bioavailability challenge of PHZ is the wide phase I and II metabolism in the digestive tract. The contribution ratio of phase II metabolism of PHZ ranged from 41.9% to 69.0% after intravenous injection with three doses of PHZ in normal rats.

The LCT (lactase-phlorizin hydrolase) cleaves lactose into its component monosaccharides and also hydrolyzes phlorizin as well as a number of other plant glycosides. A β-glucosidase activity catalyzing phlorizin hydrolysis to phloretin and glucose is present in the microvillus membrane of hamster intestinal brush border.

6.3 Altered Pharmacokinetics in Diabetes

Compared with observations for normal rats, AUC₀–t and Cmax of PHZ significantly increased and T½ of PHZ significantly decreased in type 2 diabetic rats, indicating that metabolic disease state meaningfully alters the compound's pharmacokinetic profile.

6.4 Strategies to Overcome Low Bioavailability

Novel delivery systems and synthetic derivatives, such as fatty acid esters, have shown improved pharmacokinetic profiles and efficacy. There is evidence that the "gut microbiota–barrier axis" represents an alternative target for the anti-obesity effect of phlorizin, providing an explanation for the high efficacy of phlorizin despite the low bioavailability, and suggesting that phlorizin holds great potential to be developed as a functional food ingredient.

7. Scientific Evidence by Area of Use

7.1 Glucose Metabolism and Diabetes

Preclinical Evidence

Using a partially pancreatectomized rat model of diabetes, Rosetti et al. demonstrated that the administration of phlorizin normalized fasting and post-prandial plasma glucose. In addition, administration of phlorizin in sham-operated animals had no effect on plasma glucose and insulin concentrations, indicating glucose-lowering effects specific to a diabetic metabolic context.

Preclinical studies in the 1980s showed that phlorizin improved insulin sensitivity in diabetic rat models without affecting insulin action in control rats. In diabetic rats, phlorizin treatment decreased hyperglycemia and prevented development of hypertension, decreased SGLT2 activity, but did not modify SGLT2 expression. SGLT2 inhibition prevented the development of hypertension in diabetic rats as well as hyperglycemia, suggesting a hypertensive mechanism associated with SGLT2 activity.

In a study using Lithocarpus polystachyus-derived phloridzin, diabetic rats were randomly divided into six groups including groups treated with 30 mg/kg phlorizin (low dose), 60 mg/kg phlorizin (middle dose), and 120 mg/kg phlorizin (high dose), administered by gavage once daily for 28 days.

Human/Clinical Evidence

Phlorizin itself was never advanced to formal pharmaceutical clinical trials for diabetes due to its pharmacokinetic limitations. Subsequent detection of SGLT1 and SGLT2 in the kidney, their role in glucose reabsorption, and confirmation of the inhibitory action of phlorizin on these transporters in animal studies paved the way to consider phlorizin in the treatment of type 2 diabetes mellitus. However, phlorizin was not clinically developed due to its poor pharmacokinetics and side effects attributed to SGLT1 inhibition such as glucose-galactose malabsorption, dehydration, and diarrhea.

An early human study documented in the literature by Chasis et al. in 1933 confirmed that phlorizin administration in humans caused urinary glucose excretion (glycosuria), consistent with the animal findings — but this was a physiological research study, not a therapeutic trial. Its ability to lower glucose in animals was first recognised in 1903 and confirmed in humans in 1933.

There are preliminary data from a pilot human study: a study investigated the acute anti-hyperglycaemic effects of an unripe apple preparation containing phlorizin in healthy volunteers (a preliminary study published in J Sci Food Agric, 2015). However, no large-scale, properly powered randomized controlled trials of purified phlorizin as a supplement in humans have been published. The overall strength of direct human clinical evidence for phlorizin as a glucose-lowering supplement is very weak. Its proof of concept in humans is embedded in the pharmacological history of the SGLT2 inhibitor drug class rather than in dietary supplement trials.

There are indications that consumption of average to high levels of phloridzin via food might also contribute to reduced sugar load and a reduction in T2DM risk, but this remains a research hypothesis, not an established clinical finding.

7.2 Obesity and Body Weight

Preclinical Evidence

A study investigated the ameliorating effect of phlorizin on high-fat diet (HFD)-induced obesity via modulating the "gut microbiota–barrier axis." C57BL/6J mice were fed a normal chow diet or HFD co-administered with or without phlorizin for 12 weeks. Results showed that phlorizin supplementation significantly reduced HFD-induced body weight gain, alleviated metabolic disorders like insulin resistance and elevation of serum lipopolysaccharides (LPS), attenuated HFD-induced gut microbiota alterations, enhanced short-chain fatty acids (SCFAs) production, and inhibited fecal LPS production.

A study explored the effects of dietary supplementation with phlorizin on redox state-related gut microbiota homeostasis in an obesity mouse model. Mice (C57BL/6J) were grouped for 12 weeks: normal chow diet group (NCD), high-fat and cholesterol diet group (HFD), and treatment groups fed with HFD along with three levels of phlorizin. Phlorizin alleviated the hyperlipidemia and redox status and increased the total cecal SCFA content. Additionally, phlorizin regulated gene expression related to lipid metabolism, redox status, and cecum barrier integrity, and rebuilt gut microbiota homeostasis.

Evidence strength (obesity): Currently limited to preclinical (animal) studies. No human clinical trials of phlorizin specifically for body weight management have been published.

7.3 Antioxidant Activity

In vitro and Animal Evidence

Studies demonstrated that phlorizin mitigates oxidative stress in aging models induced by d-galactose, highlighting its role in combating oxidative damage and exerting neuroprotective effects. Research showed that phlorizin reduces the oxidative injury caused by exhaustive exercise in mice through the Nrf2/ARE signaling pathway. Dietary supplementation with such compounds could help eliminate free radicals, boost the function of antioxidant enzymes like superoxide dismutase (SOD) and catalase (CAT), and inhibit lipid peroxidation.

Evidence strength (antioxidant): In vitro and animal studies only. No controlled human trials specifically measuring phlorizin's antioxidant effects have been published.

7.4 Anti-inflammatory Activity

In vitro and Animal Evidence

Phloridzin, a glycosylated derivative of phloretin, possesses a variety of biological activities, such as antidiabetic, antioxidant, anti-inflammatory, anticancer, and neuromodulatory activities. It also has antibacterial properties, but there are only a few reports on this. In cell-based experiments, phlorizin has been shown to modulate macrophage activity. These anti-inflammatory mechanisms include inhibiting the signalling pathways of inflammatory mediators' expression that support its suppressive effect in immune cell overactivation, obesity-induced inflammation, arthritis, endothelial, myocardial, hepatic, renal, and lung injury, and inflammation in the gut, skin, and nervous system, among others — all of these findings being derived from phlorizin/phloretin preclinical studies.

Evidence strength (anti-inflammatory): Predominantly in vitro and animal models. Human data are absent for phlorizin as an isolated supplement.

7.5 Anticancer Activity

Preclinical Evidence

Phloridzin, a bioactive flavonoid from Malus species, demonstrates diverse therapeutic effects including anticancer, antidiabetic, hepatoprotective, cardioprotective, neuroprotective, and antimicrobial activities. Structured literature searches highlight studies on phlorizin's anti-proliferative, pro-apoptotic, anti-inflammatory, and metabolic regulatory effects across various in vitro and in vivo cancer models. The principal mechanisms identified are glucose transporter inhibition (GLUT1/2), modulation of PI3K/AKT/mTOR and JAK2/STAT3 signaling, and suppression of metastasis and angiogenesis.

Despite compelling preclinical evidence, phlorizin's clinical application is limited by low bioavailability. Novel delivery systems and synthetic derivatives, such as fatty acid esters, have shown improved pharmacokinetic profiles and efficacy. Future studies should prioritize translational research and clinical trials to validate phlorizin's potential as an adjunct or alternative therapy in oncology.

Evidence strength (anticancer): In vitro and animal models only. No human clinical trials exist. Evidence is preliminary and mechanistically interesting, but far from clinical validation.

7.6 Neuroprotective and Cognitive Effects

Animal Evidence

A study investigated the effect of dietary supplementation of phlorizin on high-fat and high-fructose diet (HFFD)-induced cognitive dysfunction and evaluated the role of the microbiota-gut-brain axis. Dietary supplementation of phlorizin for 14 weeks effectively prevented glucolipid metabolism disorder, spatial learning impairment, and memory impairment in HFFD mice.

In Alzheimer's disease model mice (APP/PS1), phlorizin's mechanism in improving AD-related symptoms was unclear, but 8 weeks of gavage administration of phlorizin improved cognitive dysfunction and lipid disorders in APP/PS1 mice. Researchers have explored the neuroprotective properties of phlorizin and phloretin, two compounds primarily found in apples and apple pomace. Interest in their biological activities is associated mainly with their antioxidant, anti-inflammatory, and estrogenic properties.

Evidence strength (neuroprotection): Animal models only. No human clinical evidence is available for phlorizin specifically in cognitive or neurodegenerative disease contexts.

7.7 Hepatoprotective Activity

Phlorizin also has various pharmacological effects such as antiviral, antidiabetic, antitumor, and hepatoprotective effects. Studies showed that phloridzin had multiple pharmacological activities, such as antidiabetic, anti-inflammatory, antihyperglycemic, anticancer, and antibacterial activities. Beyond these, the physiological effects of phloridzin include cardioprotective, neuroprotective, hepatoprotective, immunomodulatory, and antiobesity activities.

Evidence strength (hepatoprotection): Predominantly in vitro and animal data. No controlled human trials.

7.8 Renal Physiology Effects

In studies on kidney function in diabetic animal models, it was discovered that phloridzin could inhibit renal glucose reabsorption and cause glucosuria. One study in diabetic rats administered phlorizin at a total of 400 mg/kg subcutaneously (split into two 200 mg/kg doses) on the first day; the dose was raised to 400 mg/kg twice daily and treatment was continued for 6 days. That study found that phlorizin treatment decreased hyperglycemia and prevented development of hypertension in diabetic rats, and decreased SGLT2 activity in brush border membrane vesicles but did not modify SGLT2 expression.

7.9 Parentage of the Gliflozin Drug Class

Perhaps phlorizin's most consequential scientific legacy is as the template for an entire class of approved medicines. Phlorizin was the first SGLT inhibitor discovered. This compound was superseded by better and more selective synthetic analogs like canagliflozin, dapagliflozin, and empagliflozin. Empagliflozin, a newer SGLT2 inhibitor in current clinical use, has improved potency, longer half-life, and better oral availability compared with phlorizin. It wasn't until 2013 that canagliflozin became the first approved diabetes medicine to target SGLT.

8. Body Systems and Health Areas Associated with Phlorizin

• Endocrine / Metabolic System: Phlorizin, as the specific and competitive inhibitor of SGLT1/2, is able to reduce blood glucose by downregulating intestinal and renal glucose absorption, restore normal blood glucose levels and normalize insulin sensitivity, and improve dyslipidemia and diabetic complications in diabetic rodent models.
• Renal System: Phlorizin lowers plasma glucose by enhancing renal glucose excretion independent of insulin secretion.
• Gastrointestinal System: Phlorizin blocks intestinal glucose absorption through inhibition of the sodium glucose transporters located in the mucosa of the small intestine.
• Cardiovascular System: Phloridzin's physiological effects include cardioprotective activities.
• Central Nervous System: Phlorizin, recognized for its bioactive properties including modulation of glucose and lipid metabolism, has neuroprotective effects against diabetes-related cognitive dysfunction that have not been fully elucidated.
• Hepatic System: Hepatoprotective effects have been documented in cell culture and animal studies, as noted in multiple preclinical reviews.
• Gut Microbiome: The "gut microbiota–barrier axis" appears to be an alternative target for the anti-obesity effect of phlorizin.
• Immune / Inflammatory System: Phlorizin alters metabolic pathways in human macrophages to reduce inflammation.

9. Dosage Forms and Doses Reported in Studies

No standardized supplement dosage for phlorizin has been established by any regulatory or pharmacopoeial body. The following are doses reported in research sources only:

• Dietary (naturally occurring): European people consume, on average, 0.7–7.5 mg/d of phloridzin; however, high-level consumers may eat up to 52 mg/d.
• Animal studies — oral/gavage (diabetes models): Phlorizin groups in one rat study were treated with 30 mg/kg (low dose), 60 mg/kg (middle dose), and 120 mg/kg (high dose) by gavage once daily for 28 days.
• Animal studies — subcutaneous (renal physiology): In one rat protocol, the first day's total dose was 400 mg/kg phlorizin subcutaneously, split into two 200 mg/kg doses; the second day the dose was raised to 400 mg/kg twice daily for 6 days.
• Animal studies — oral (obesity model): In HFD-STZ-induced diabetic rats, phlorizin was orally administered for 4 weeks. A lower dose of phlorizin (20 mg/kg) augmented unfavorable musculoskeletal outcomes of diabetes, while at a higher dose (50 mg/kg), musculoskeletal parameters were not significantly affected.
• In vitro peritoneal use (research model): In one experimental rat peritoneal dialysis study, intraperitoneal phlorizin was used at 50 mg/L concentration in the dialysis fluid.

Phlorizin is commercially available as a research-grade chemical and is present in some dietary supplement products, typically as an extract standardized to phlorizin content from apple bark or related sources. Supplement forms include capsules, powders, and standardized apple polyphenol extracts. No peer-reviewed human clinical trial has established a safe or effective supplement dose range for phlorizin.

10. Safety Considerations and Interactions

10.1 Fundamental Safety Constraints

Confirmation of the inhibitory action of phlorizin on SGLT1 and SGLT2 transporters in animal studies paved the way to consider phlorizin in the treatment of type 2 diabetes. However, phlorizin was not clinically developed due to its poor pharmacokinetics and side effects attributed to SGLT1 inhibition such as glucose-galactose malabsorption, dehydration, and diarrhea.

Phlorizin is poorly absorbed when taken by mouth, but is well tolerated in humans by injection, and has been used as a research tool to demonstrate the existence of glucose toxicity.

10.2 SGLT1-Related Gastrointestinal Effects

Because phlorizin inhibits both SGLT1 (intestinal) and SGLT2 (renal), unlike the selective SGLT2-inhibitor drugs approved for clinical use, intestinal side effects are a relevant concern with pharmacological doses. Non-selective action on intestinal SGLT1 causes significant gastrointestinal adverse effects and intolerance — as was established when the SGLT1/2-non-selective drug T-1095 (a phlorizin analog) was developed and subsequently abandoned. These same concerns are relevant to phlorizin itself at doses above dietary levels.

10.3 Risk of Glycosuria and Volume Depletion

Von Mering demonstrated that doses greater than 1 gram daily produced glycosuria in animal experiments. At pharmacological doses, phlorizin-induced glycosuria could theoretically cause dehydration, electrolyte imbalances, and — in patients on antidiabetic medications — hypoglycemia (by additive glucose-lowering effects), though this has not been formally studied in human supplement contexts.

10.4 Drug Interactions

Phlorizin can also be applied in combination with other antidiabetic agents such as metformin for effective management of glucose metabolism, as shown in animal work. However, this also implies that persons taking SGLT2 inhibitor drugs (gliflozins), sulfonylureas, insulin, or other glucose-lowering agents could experience additive or synergistic effects on blood glucose. No formal human drug–supplement interaction studies have been published for phlorizin.

10.5 Traditional Safety Record

The clearest long-term safety data come from the traditional use of phlorizin-containing sweet tea. The tender leaves of Lithocarpus polystachyus, called Sweet Tea in southern China, have been commonly used as a sweet tonic beverage and traditional herb, taken for hundreds of years without evidence of adverse effects or toxicity. This historical record pertains to the whole plant material consumed as a beverage at typical dietary concentrations, not to isolated, purified phlorizin at supplement doses.

10.6 Musculoskeletal Considerations at Higher Doses

In HFD-STZ-induced diabetic rats, phlorizin was orally administered for 4 weeks. The diabetic animals showed a significant decrease in muscle mass/strength and marked osteoporotic changes; these unfavorable outcomes of diabetes were significantly augmented by a lower dose of phlorizin (20 mg/kg). This animal finding — that lower doses of phlorizin under diabetic conditions may worsen musculoskeletal parameters — warrants caution and highlights that phlorizin's effects are dose- and context-dependent.

10.7 Context Within the SGLT Pharmacology Literature

Based on the inhibition of glucose reabsorption from pre-urine, the glucose-lowering effect of SGLT-inhibition only occurs in a hyperglycemic/glycosuric state and, through an action independent of insulin, is not associated with a hypoglycemic risk, even in non-diabetic subjects — at least as established for the approved pharmaceutical SGLT2 inhibitors. Whether this applies equivalently to natural phlorizin (which also inhibits SGLT1 and has minimal oral bioavailability) cannot be directly inferred.

Summary of Evidence Quality

Phlorizin occupies a scientifically distinguished position as the founding natural compound of the SGLT inhibitor pharmacological class, and its study over nearly two centuries has substantially advanced the understanding of renal glucose physiology. Nevertheless, as a dietary supplement or nutraceutical, the direct human clinical evidence base for phlorizin remains extremely limited. Despite compelling preclinical evidence, phlorizin's clinical application is limited by low bioavailability. Several laboratory-based studies indicate that phloridzin plays a significant role against many vital diseases, showing various actions such as antimicrobial, antioxidant, antiobesity, antiaging, cardioprotective, hypolipidemic, hepatoprotective, immunomodulatory, neuroprotective, anti-inflammatory, antidiabetic, antihypertensive, antihyperglycemic, antitumor, etc., but essentially all of these findings come from in vitro cell studies or animal models. Rigorous, adequately powered randomized controlled trials in humans have not been published for purified phlorizin as a supplement for any indication.

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