Capers (Capparis spinosa L.): A Comprehensive Reference
1. Identity: Botanical Classification, Source, and Common Forms
Botanical and Taxonomic Identity
Capparis spinosa L. is a perennial shrub of the family Capparaceae, endemic to circum-Mediterranean countries. It is also known by synonyms including C. rupestris and C. ovata Desf., and is a dicotyledonous perennial shrub found throughout the Mediterranean countries of Europe, Asia, and North Africa, where it prefers dry heat and intense sunlight. Also called the "Flinders rose," the taxonomic status of the species is controversial and unsettled. Species within the genus Capparis are highly variable and interspecific hybrids have been common throughout the genus's evolutionary history. As a result, some authors have considered C. spinosa to be composed of multiple distinct species, others that the taxon is a single species with multiple varieties or subspecies, or that it is a hybrid between C. orientalis and C. sicula.
It is believed that capers are indigenous to the Mediterranean basin, but their probable origin is the dry areas in western and central Asia. Although native to the Mediterranean, the plant grows well in Italy, Northern Africa, Greece, Central Asia, Iran, and other parts of the world.
Plant Morphology
The shrubby plant is many-branched, with alternate leaves that are thick, shiny, and round to ovate. The flowers are complete, sweetly fragrant, and showy, with four sepals and four white to pinkish-white petals, many long violet-coloured stamens, and a single stigma usually rising well above the stamens. From mid-April to the end of September, capers may grow 1 to 1.5 m in height, spread 2 to 3 m, and bud white flowers up to 7.6 cm across. Caper is salt tolerant and resistant to drought, grows up to 4 m in height in warm and dry weather, and has extensive root systems which can extend up to 6–10 m.
What "Capers" Are: Edible Plant Parts
Unopened flower buds of Capparis spinosa L. (capers), generally used in the Mediterranean area as food flavoring, are known to be a good source of bioactive compounds. The plant is best known for these edible flower buds, used as a seasoning or garnish, and the fruit (caper berries), both of which are usually consumed salted or pickled. Other species of Capparis are also picked along with C. spinosa for their buds or fruits. Other parts of Capparis plants are used in the manufacture of medicines and cosmetics.
Capers and caperberries are distinct products. If an immature caper bud is left on the plant, it eventually matures into a caperberry fruit. Caperberries are bigger than capers, usually about the same size as an olive, with a long stem attached.
Common Commercial Forms and Preparations
The unripened buds must first be dried in the sun, then pickled in vinegar, brine, wine, or salt to become the characteristic salty green pea-sized condiment. Curing brings out their tangy lemon flavour, similar to that of green olives. Salted capers are coated in salt for preservation, making their flavor more intense and the texture firmer compared to brined capers, which are stored in vinegar or brine. Salted capers generally need to be rinsed before use, while brined capers have a slightly tangy taste from the pickling liquid and may not require rinsing.
In commercial practice, capers are categorized by their size in the markets. Small buds fetch more value than large ones. Non-pareil and surfines are some of the small bud types, while capucines, capotes, and grusas fall into the big-size category.
Beyond culinary use, immature small leaves are also eaten as a vegetable or pickled and used in salads and fish dishes. The fruits (i.e., caperberry, capperone, taperone) are used in sauces or pickled and eaten similar to small gherkins. The strong flavor of capers comes from mustard oil, specifically methyl isothiocyanate.
2. Historical and Traditional Use
Ancient Origins
Wild caper berries were mentioned in the Sumerian Epic of Gilgamesh, an epic poem written in Mesopotamia more than 4,000 years ago. Archaeobotanical evidence of capers has been found in the Mediterranean region and Mesopotamia as early as the Upper Paleolithic period. Caper seeds and dried roots have been found in tombs in China, Egypt, India, Iran, and Turkey.
References are found in the Bible, in the writings of Hippocrates, Aristotle, and Pliny the Elder, both for food and medicinal use. Since ancient times, the widespread belief has attributed aphrodisiac properties to the caper. Athenaeus in Deipnosophistae pays considerable attention to the caper, as do Pliny (NH XIX, XLVIII.163) and Theophrastus.
Greek and Roman Use
The ancient Greeks applied capers as a carminative, included them as an ingredient in cooking, and used the roots and leaves for medicinal purposes. Ancient Greeks and Romans used capers for reducing flatulence, to aid slimming, and as an aphrodisiac. The Romans also used capers to stimulate the appetite and to treat a variety of illnesses from toothache, paralysis, and fevers to erectile dysfunction.
Ayurvedic, Arabian, and Traditional Asian Medicine
Capparis spinosa is called the "Plant of the Millennium," and it has highly diverse economic and medicinal value in different systems of medicine, including Iranian, Unani, Chinese, Ayurvedic, and Greco-Arabic traditions.
In ancient Greece, the caper was used as a carminative (relieving flatulence), whereas records of Ayurvedic medicine include its use to improve liver function. Capers have been used in traditional Arabian medicine for diabetes as well as an emmenagogue. Capers have also been used for arteriosclerosis, diuresis, as a kidney disinfectant, and as vermifuges and tonics.
In traditional medicine and indigenous knowledge, roots are used as diuretic, astringent, and tonic; root bark has been used as an appetizer. The consolidated traditional use of the root as a remedy against different pains in humans is well known since antiquity.
Traditional Preparations
Seeds of the caper were traditionally used to preserve wine and relieve toothache, while infusions and decoctions from the root bark were employed in various traditional contexts. The caper berry was considered healthy by the Greeks, who made a herbal tea from the roots to counteract rheumatism and inflammation. Caper parts have also been used to relieve rheumatic pain in traditional medicines. The pickled fruits of caper are eaten at the dose of 2–8 g daily as a remedy by diabetic patients in Iran.
Jewish and Biblical Context
The Mishna describes capers, called kahfars or tzalaf, as a kind of "budding fruit" and tithable crop that was widely grown in Judea. At that time, caper berries were often employed to produce caper wine, which was one of the ingredients of the ketoret—an incense made with a blend of herbs and balms used as an offering on Yom Kippur.
3. Key Constituents and Active Compounds
Primary Phytochemical Classes
The major phytochemicals identified in caper were flavonoids (rutin, quercetin, and catechin), alkaloids (indoles and spermidines), and glucosinolates (glucocapparin). Other constituents such as furan and pyrrole derivatives as well as polyunsaturated fatty acids — represented mainly by oleic acid, linoleic acid, and palmitic acid — were also among the most important groups of chemicals found in caper.
Phytochemical analyses have revealed that C. spinosa leaves are particularly abundant in polyphenolic compounds, especially flavonoids such as rutin, quercetin-3-glucoside, and catechin. HPLC analysis has also revealed compounds including rutin, resveratrol, coumarin, epicatechin, luteolin, catechin, kaempferol, vanillic acid, and gallic acid.
Rutin
Capers are also noted as one of the most significant dietary sources of rutin, which is also found in much smaller concentrations in olives and other fruits and vegetables. Rutin is a flavonol glycoside (quercetin-3-rutinoside) that has been extensively studied for its antioxidant and anti-inflammatory properties. Among the 24 detected compounds found via HPLC-ESI/MS in Pantelleria salt-fermented capers, several flavonol derivatives and glucosinolates were identified. The levels of kaempferol and quercetin derivatives varied considerably among accessions studied.
Glucosinolates
The seed oil is rich in unsaturated and rare lipids such as cis-vaccenic acid, and the main glucosinolate is glucocapperin, and the main flavonoid is rutin. The strong pungent flavor of the caper comes from mustard oil, specifically methyl isothiocyanate, which is a hydrolysis product of these glucosinolates.
Alkaloids
Alkaloids have been isolated from the roots and fruits of caper. Identified alkaloid constituents include stachydrine, indole derivatives (such as capparilosides A and B), and spermidine-type compounds, as indexed in the PubMed literature.
Seed Oil and Fatty Acids
Caper seed is an inexpensive source of omega-6, and its seed oil is regarded as an oleic-linoleic oil. Caper seeds have been declared an important source of antioxidant molecules for the food and pharmaceutical industries as they are rich in phenolic compounds and show high antioxidant activity.
Vitamin and Mineral Profile
Results from phenolic profiling studies showed the richness of caper with phenolic compounds, especially in flower buds. Both α- and γ-tocopherol were found in buds, and C. spinosa contained an appreciable level of vitamin C. The significant amounts of these antioxidants confirm the nutritional and medicinal value of the caper. In a 100-gram amount of canned capers, the sodium content is 2,350 mg (102% DV), with vitamin K (21% DV) and riboflavin (11% DV) also having appreciable levels.
4. Mechanisms of Action
Antioxidant Mechanisms
In vitro assays have revealed caper extracts' strong antioxidative properties, effectively safeguarding Caco-2 and HepG2 cells against oxidative stress and significantly lowering reactive oxygen species (ROS) levels. Pretreatment with hydroalcoholic fraction at the dose of 400 mg/kg and quercetin at the dose of 20 mg/kg showed liver protection against t-BHP-induced hepatic injury. The possible mechanism of this protection may be associated with the property of scavenging free radicals due to the presence of phenolic compounds.
Anti-inflammatory Mechanisms
Capparis spinosa aqueous fraction appeared to induce an overall anti-inflammatory response through significant inhibition of IL-17 and induction of IL-4 gene expression when PBMCs were treated with non-toxic doses of 100 and/or 500 μg/mL. In an animal study, a significantly reduced edema was detected in mice treated with C. spinosa preparations relative to control, and this effect was dose-dependent and statistically similar to that observed with indomethacin.
Antidiabetic Mechanisms
The putative mechanisms involved in the antihyperglycemic effects of C. spinosa include reducing carbohydrate absorption from the small intestine, inhibiting gluconeogenesis in the liver, enhancing glucose uptake by tissues, and beta cell protection/regeneration.
Neuroprotective Mechanisms
An aqueous extract of caper rich in rutin and quercetin was shown to attenuate cognitive impairment and reduce inflammation by modulating Alzheimer's-related genes such as BACE1, APP, PSEN1, and PSEN2. β-Secretase (BACE1) plays a central role in the generation of Aβ peptides and is considered a key therapeutic target in Alzheimer's disease. In network pharmacology analyses, BACE1 was predicted to be targeted by kaempferol, apigenin, and ginkgetin among the C. spinosa-derived compounds.
5. Scientific Evidence by Area of Use
5.1 Glycemic Control and Type 2 Diabetes
The most clinically advanced area of research for caper relates to blood glucose modulation. A randomized clinical trial was conducted in 54 type 2 diabetic patients. Two groups of 28 and 26 patients, respectively on standard anti-diabetic therapy, received 400 mg caper fruit extract or placebo capsules three times a day for two months. Results showed a significant decrease in fasting blood glucose levels (p=0.037) and glycosylated hemoglobin (p=0.043) in caper-treated patients compared to the control group at the end of the study period. The conclusions indicated that caper fruit extract may be a safe anti-hyperglycemic and anti-hypertriglyceridemic agent for type 2 diabetic patients.
A second human study also employed a caper-based preparation: the aim of that randomized triple-blind placebo-controlled clinical trial was to investigate the safety and efficacy of C. spinosa oxymel on blood glucose, lipid profile, and other diagnostic indexes of metabolic syndrome in patients with poorly controlled type 2 diabetes. The C. spinosa oxymel was prepared by adding hydroalcoholic extract of C. spinosa fruit to simple oxymel (a mixture of grape vinegar and lactulose). Thirty diabetic patients with metabolic syndrome whose glycemic status was not controlled despite receiving full doses of oral hypoglycemic agents and who did not want to start insulin therapy were randomly allocated to groups.
A further human study used a mixed plant preparation: a mixture of plant materials including caper was used to assess efficacy in patients with type-2 diabetes mellitus; the plant mixture reduced fasting plasma glucose and glycated hemoglobin (HbA1c) compared to placebo and showed similar results compared to metformin-treated patients. However, this study's results cannot be attributed to caper alone, as it involved multiple plant ingredients.
Evidence strength: Preliminary. There are a small number of randomized controlled trials with limited sample sizes (30–60 patients). While results are promising, they do not yet constitute sufficient evidence for a clinical recommendation. Several studies have showed the antihyperglycemic and hypolipidemic activities of C. spinosa, though replication in larger, independent trials is needed.
5.2 Hepatoprotection (Liver Protection)
Studies have investigated the antioxidant and hepatoprotective effects of Capparis spinosa L. and quercetin in tert-butyl hydroperoxide (t-BHP)-induced acute liver damage. Pretreatment with the hydroalcoholic fraction at 400 mg/kg showed liver protection against t-BHP-induced hepatic injury, as evidenced by a significant decrease in serum enzyme markers. Abundant flavonoid compounds such as quercetin are considered the main hepatoprotective factor in the hydroalcoholic extract of C. spinosa.
Protective action of C. spinosa ethanolic root bark extract was evaluated in an animal model of hepatotoxicity induced by carbon tetrachloride. C. spinosa root bark extract exhibited significant hepatoprotective activity against CCl4-induced liver damage in mice. The study employed doses of 100, 200, and 400 mg/kg, with 400 mg/kg showing the most efficacy. Serum ALT and AST levels significantly decreased in treated groups, indicating liver function improvement, and histopathological analysis revealed reduced necrosis and inflammation.
A clinical trial investigating the efficacy of a mixed preparation containing caper extract combined with other extracts found an improvement in liver function laboratory values, although again the contribution of caper as a single agent cannot be isolated in this context. The combination therapy Liv-52® (Himalaya Herbals, India), which contains ferric oxide, capers, and several other herbal ingredients, may be an effective treatment for cirrhosis. However, the efficacy of capers alone for cirrhosis or other conditions remains unproven.
Evidence strength: Predominantly animal and in vitro data. The human clinical evidence is indirect (multi-ingredient preparations), and no well-powered human clinical trial has evaluated caper extract as a standalone hepatoprotective agent.
5.3 Anti-inflammatory Effects
An in vitro study aimed to evaluate immunomodulatory properties of Capparis spinosa leaf extracts on human peripheral blood mononuclear cells (PBMCs) from healthy individuals. The aqueous fraction of C. spinosa appeared to induce an overall anti-inflammatory response through significant inhibition of IL-17 and induction of IL-4 gene expression when PBMCs were treated with non-toxic doses of 100 and/or 500 μg/mL.
An in vivo study assessed the ability of Capparis spinosa preparation to orientate the immune response mediated by CD4+ T cells towards an anti-inflammatory response, using the contact hypersensitivity model in Swiss mice. Histology studies revealed that C. spinosa induced a significant decrease in immune cell infiltration and vasodilation.
Caper flavonoids are known to have anti-allergic, anti-diabetic, anti-inflammatory, antibacterial, and anti-hepatotoxic properties. Caper extract has also been reported to exhibit notable activity in protection against oxidative stress and interruption of the ROS-ERK1/2-Ha-Ras signal loop in systemic sclerosis. Researchers have also reported a chondro-protective effect of caper extract in inflammatory joint diseases.
Evidence strength: Predominantly in vitro and animal model data. No standalone human clinical trials specifically examining anti-inflammatory endpoints have been published. Human cell-based studies provide mechanistic plausibility but do not constitute clinical evidence.
5.4 Antimicrobial Activity
Caper extracts have furnished promising antimicrobial activities in different experimental models. For instance, the methanol extract of the fruits showed a dose-dependent degree of quorum sensing, expressing 70–79% of biofilm inhibition and 46–67% reduction of exopolysaccharide production in Serratia marcescens, Pseudomonas aeruginosa, and Escherichia coli.
Evidence strength: In vitro only. No human clinical studies have evaluated capers for infectious disease indications. This area of evidence remains entirely preclinical.
5.5 Neuroprotective Effects
Research has demonstrated that C. spinosa extracts possess neuroprotective properties. For instance, an aqueous extract of caper rich in rutin and quercetin was shown to attenuate cognitive impairment and reduce inflammation by modulating Alzheimer's-related genes such as BACE1, APP, PSEN1, and PSEN2.
Evidence strength: Preclinical (animal and in vitro). No clinical trials in human populations have examined neuroprotective or cognitive endpoints.
5.6 Antioxidant Activity
Caper carries a renowned nutritional value, especially in terms of vitamins and antioxidants related to the occurrence of flavonoids, alkaloids, and glucosinolates as main secondary metabolites. The administration of hydro-alcoholic extract of caper fruits demonstrated protective effects on tissue function through oxidative stress alleviation and antioxidant mechanism restoration in animal models.
Evidence strength: Well-established in vitro and animal data. Human interventional data on caper-specific antioxidant outcomes are limited; however, the constituent compounds (rutin, quercetin, kaempferol) are individually well-characterized antioxidants across independent lines of research.
5.7 Anticancer Activity
C. spinosa possesses various biological activities including antioxidant, antidiabetic, anticancer, hepatoprotective, neuroprotective, anti-inflammatory, anti-arthritic, antibacterial, and insecticidal effects, based on in vitro and animal evidence reviewed in the scientific literature. Studies indicate that caper and its bioactive compounds may help manage metabolic conditions like diabetes and hyperlipidemia, while also exhibiting anticancer, hepatoprotective, and cardioprotective effects.
Evidence strength: Entirely preclinical. All anticancer observations for C. spinosa are in vitro or in animal models. No human clinical trials examining cancer outcomes have been conducted.
5.8 Renal (Kidney) Protection
Capparis spinosa is traditionally used to treat liver and kidney diseases. One study explored the antioxidant, nephroprotective, and hepatoprotective effects of methanolic extract of Capparis spinosa leaves (MECS) associated with its phytochemical content. The MECS treatment significantly reduced the increased plasma levels of creatinine, urea and uric acid, reduced elevated MDA levels, and restored the kidney damage provoked by cisplatin treatment in an animal model.
Evidence strength: Animal model data only. No human clinical trials have evaluated renal protection endpoints.
6. Body Systems and Health Areas of Association
Based on the peer-reviewed literature, Capparis spinosa has been associated with effects on the following body systems:
- Metabolic system: Glycemic regulation, lipid-lowering, and management of metabolic syndrome parameters — supported by the most robust (though still limited) human clinical evidence.
- Hepatic system: Liver enzyme normalization, hepatocyte protection from oxidative insult, attenuation of hepatic inflammation and fibrosis — primarily animal and in vitro evidence, with limited indirect human data.
- Immune and inflammatory system: Cytokine modulation (IL-17 inhibition, IL-4 induction), inhibition of inflammatory cell infiltration — human cell culture (PBMCs) and animal data.
- Central nervous system: Attenuation of cognitive impairment, modulation of Alzheimer's-associated gene pathways — preclinical only.
- Renal system: Nephroprotection, reduction of markers of kidney injury — animal model data only.
- Cardiovascular system: Cholesterol-lowering, antioxidant, and anti-inflammatory effects have been shown for C. spinosa in animals. Research has found that C. spinosa extract can significantly lower blood sugar and cholesterol levels in diabetic rats.
- Musculoskeletal system: Traditional use for rheumatic pain and in vitro evidence of chondroprotective effects.
- Gastrointestinal system: Traditional use as a carminative and appetite stimulant.
7. Dosage Forms and Doses Reported in Studies
Limited adequate clinical evidence exists to guide dosage. The following dosages are drawn specifically from the cited studies:
- Diabetes (human RCT): 1,200 mg (400 mg three times daily) of caper fruit extract given over 2 months was used in a small clinical trial.
- Diabetes (ethnobotanical practice): Ethnobotanical medicinal use for diabetes includes doses of 2 to 8 g of caper fruit eaten per day.
- Diabetes (human RCT — oxymel preparation): A randomized triple-blind placebo-controlled clinical trial investigated C. spinosa oxymel — a hydroalcoholic extract of C. spinosa fruit added to simple oxymel (grape vinegar and lactulose).
- Hepatoprotection (animal study): Doses of 100, 200, and 400 mg/kg in mice, with 400 mg/kg showing the most efficacy.
- Hepatoprotection (animal study — hydroalcoholic fraction): Pretreatment with hydroalcoholic fraction at the dose of 400 mg/kg and quercetin at the dose of 20 mg/kg showed liver protection against t-BHP-induced hepatic injury.
- In vitro immunomodulation: Non-toxic doses of 100 and/or 500 μg/mL of Capparis spinosa aqueous fraction induced anti-inflammatory cytokine response in PBMCs.
- Antidiabetic (animal): A lower dose of aqueous extract (20 mg/kg) showed a decrease in blood glucose level from 19.81 to 5.59 mM after a single oral administration in rats.
No standardized dosage forms have been approved by major regulatory agencies (EMA, FDA) specifically for Capparis spinosa as a medicinal product.
8. Safety Considerations and Notable Interactions
General Safety Profile
Capers are generally recognized as safe (GRAS) when used as food. There is limited evidence of adverse effects with use of capers.
Sodium Content as a Practical Concern
In a 100-gram amount of canned capers, the sodium content is 2,350 mg or 102% of the daily value. This high sodium level is mainly due to the addition of sea salt (sodium chloride) in the brine. This is a substantive dietary consideration for individuals following low-sodium diets or managing hypertension and heart or kidney disease.
Allergic Contact Dermatitis
Topical use of capers may cause contact dermatitis. Food allergy has also been reported. Plants of the caper family (Capparaceae), which is the tropical relative of the mustard family (Cruciferae), yield "mustard oil" (isothiocyanate). A review of reported effects on the skin and mucous membranes of these plants and of their geographical distribution found that plants which yield isothiocyanates can produce irritant dermatitis and some can probably produce allergic contact dermatitis. Rash has been reported when capers were applied to the skin in a wet compress.
Cross-Sensitivity
Cross-sensitivity with mustard oil may be possible. This is mechanistically consistent with the shared isothiocyanate chemistry between the Capparaceae and Brassicaceae (mustard) families.
Food Allergy
Food allergy to caper (Capparis spinosa) has been documented in the peer-reviewed literature (J Investig Allergol Clin Immunol, 2013;23(1):67–69).
Use in Pregnancy
Capers have been used in traditional Arabian medicine as an emmenagogue and should be avoided in pregnancy based on traditional contraindications, though formal clinical studies on this specific concern are lacking.
Histamine Content
Capers are considered a high histamine food. Histamines are naturally occurring compounds in a variety of foods, including fermented or preserved foods like capers. This can potentially cause issues for individuals with histamine intolerance, a condition where the body is unable to effectively break down histamines, leading to symptoms such as headaches, itchy skin, and gastrointestinal issues.
Drug Interactions
No well-documented drug interactions with capers have been established. However, based on pharmacological findings, additive or synergistic effects with oral hypoglycemic agents are plausible and were the design consideration in the clinical trials described above, where patients were already on standard anti-diabetic therapy. Theoretical interactions with anticoagulants may exist given the vitamin K content, though this has not been specifically studied.
Hypoglycemia Risk
Based on the clinical trial finding of significant fasting blood glucose reduction in patients already receiving antidiabetic medications, the results suggest that caper fruit safely improves hyperglycemia and hypertriglyceridemia in type 2 diabetic patients when used adjunctively, but this also implies the potential for additive hypoglycemia if blood glucose is not monitored.
References
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