Capers are a delicious addition to Mediterranean meals for some, while for others these small flower buds are inedibly bitter. But aside from their intriguing taste, capers have antioxidant, anti-inflammatory, and antidiabetic effects, for which they have been traditionally used for millennia. Read on to learn more about capers, their active compounds, health benefits, and side effects.

What are Capers?

Capers are the immature flower buds of the caper bush (Capparis spinosa L.). Its fruits, caper berries, are also edible. This plant grows wild in arid and semi-arid zones of the Mediterranean, most of Asia, the Pacific Islands, Eastern Africa, Madagascar, and even Australia [1+, 2+].

The caper bush starts growing after spring rains (April-May), disappears when temperatures drop (September-October), and survives winter as a stump. It can grow in poor, rocky soils and resists drought and high temperatures [1+, 2+].

Capers and caper berries have been consumed for at least 9,000 years. Ancient civilizations also used them as a medicine for [1+, 3]:

  • Spleen disease (Arab)
  • Paralysis, pain relief, and erection disorders (Roman)
  • Convulsions (Greek)

Although traditionally collected from wild plants, capers have also been cultivated for 40 years. The main producers are Turkey, Morocco, Spain, Italy, France, and Tunisia while the main importers are the US and the UK [1+, 3].

Capers are pickled in vinegar and salt and used as an appetizer or as a seasoning. Capers are much appreciated for their sharp, pungent flavor and included in several dishes, such as [3]:

  • Sauces
  • Salads
  • Cold dishes
  • Meats
  • Salmon dishes
  • Pasta
  • Pizza

Caper buds and fruits have many active compounds and are used traditionally in several countries to improve conditions such as [1+, 4+, 5]:

  • Diabetes (Morocco)
  • Water retention, malaria, hemorrhoids, and joint disease (Iran)
  • Boils (India)
  • Gout, paralysis, spleen disease, pain, and rheumatism (China)
  • Lung disease, erection difficulties, pain, and rheumatism (Israel)

This article will focus on Capparis spinosa. Other related species such as C. sicula and C. orientalis are also commonly called ‘capers’ and used as food and medicinal plants but may have a different composition and distinct health benefits [1].

Snapshot of Capers

Pros:

  • Very tasty
  • Rich in antioxidants
  • Anti-inflammatory
  • Source of vitamins and fiber
  • Low in calories

Cons:

  • Raw capers are very healthy and low in salt but extremely bitter
  • Even cured capers are too bitter or salty for some people
  • High sodium content (if cured in brine and salt)
  • Insufficient evidence for most benefits

Active Components

The main active components of capers are phenols (1 – 3%), such as the following flavonoids [6+, 5+]:

  • Quercetin and its derivatives (especially rutin) [7, 8]
  • Kaempferol and its derivatives [9]
  • Ginkgetin and isoginkgetin [10]

Other active compounds found in capers include:

  • Alkaloids (capparisine A, B, and C, flazin, guanosine, capparin A and B) [11, 12+]
  • Sulfur-containing glucosinolates (glucocapparin, glucobrassicin, and their derivatives) and their antioxidant breakdown products (isothiocyanates or ‘mustard oil’) [13, 14, 15]
  • Carotenoids (e.g., pro-vitamin A), terpenoids (e.g., vitamin E), and vitamin C [16, 6]
  • Complex sugars, polysaccharides [17]

The phenolic and vitamin content strongly depends on where and how capers were cultivated. In two studies comparing capers grown in different Mediterranean countries, Tunisian capers were the richest in flavonoids, Italian capers had the highest rutin content, Moroccan capers had the highest vitamin A content, and Spanish capers contained the highest vitamin E levels [6+, 18].

Capers and caper berries are typically fermented in brine to reduce their bitterness. During this process, part of the rutin is broken down to quercetin. This is also the step when salt is added, sometimes in very high amounts [19].

Storage conditions have no effect on the antioxidant phenols content, but can greatly reduce the levels of carotenoids, vitamin E, and vitamin C in capers [1+].

Nutrition Facts

The nutritional value of canned capers per 100g is [20+, 16+, 6+]:

Capers nutrition facts

This makes cured, canned capers very high in salt but low in calories.

Capers are healthier if you can eat them raw, if you cook fresh capers, or cure them yourself without adding too much salt and brine. Alternatively, canned capers could be used as a salt substitute. In that case, you don’t need to add additional salt to your meal. You could also rinse the canned capers to wash out some of the added salt.

Mechanisms of Action

1) Antioxidant Mechanisms

Free radicals (and ROS) can build up in the body to damage DNA, proteins, and important fatty molecules. Antioxidant compounds in capers can prevent this by [21+, 22+]:

  • Breaking down free radicals and ROS
  • Blocking the enzymes and retaining minerals needed to produce them
  • Boosting the levels of antioxidant molecules and enzymes

The most abundant antioxidant molecules of capers are rutin, quercetin, kaempferol, proanthocyanidins, carotenoids, and vitamins E and C [23, 16, 24, 25].

The antioxidant effects of capers extracts have been proven in the liver, heart, and brain of mice [26, 27, 28].

2) Anti-Inflammatory Mechanisms

In arthritic rats, a Chinese medicine based on capers reduced the production of two inflammatory proteins (TNF-alpha and IL-1beta) and the blood levels of Th17 cells [29].

Caper’s essential oil, mainly composed of rutin and chlorogenic acid, and its flavonoids ginkgetin and isoginkgetin blocked the master inflammatory pathway NF-kB in two cellular studies [30, 10].

Capers extract will have different effects depending on which active compounds its most rich in.

In immune cells (dendritic cells) exposed the LPS toxin, extracts with the fewer flavonoids and more polysaccharides blocked cells from maturating and reduced the production of immune activators (CD40 and CD80) and inflammatory proteins (IL-6, IL-1beta, and TNF-alpha). But extracts richer in flavonoids and lower in polysaccharides increased cell development and immune activators [17].

This means that the polysaccharides in capers have a greater potential to lower inflammation and autoimmunity than flavonoids. This may hold true for people with leaky gut too, as the bacterial toxin LPS can enter their bloodstream when the gut barrier is damaged.

On the other hand, flavonoids can over-stimulate the immune system. This can be harmful to Th1/Th17-dominant people suffering from autoimmune diseases or chronic inflammation.

3) Anti-Cancer Mechanisms

In several studies, caper fruit extracts killed liver and stomach cancer cells by [31, 32, 27]:

  • Reducing the production of proteins that help cancer cell survive (Bcl-2) while inducing ones that trigger cell death (Bax)
  • Activating two cell death proteins (caspase-3 and caspase-9)
  • Increasing ROS levels in cancer cells and disturbing their calcium balance

Caper’s essential oils and its flavonoids rutin and chlorogenic acid didn’t kill liver cancer cells but prevented their division in one study [30].

4) Anti-Diabetic Mechanisms

Caper fruit extract lowered blood sugar levels in diabetic rats and obese mice but not in healthy animals. The extract didn’t affect insulin levels but instead probably increases sugar breakdown and insulin sensitivity. It may also reduce sugar uptake in the gut (by slowing digestion) [33, 34+].

5) Antiviral Mechanism

A caper bud extract rich in flavonoids inhibited the genital herpes virus by stimulating Th1 cells to mount an immune response (via IL-12, IFN-gamma, and TNF-alpha) [35].

Health Benefits of Capers

1) Capers May Improve Diabetes

It’s been long believed that capers can lower blood sugar levels. Diabetics in countries like Morocco, Israel, Jordan, and Iran eat capers seeking this benefit [36, 37+, 38+, 39].

In a clinical trial on 54 people with type 2 diabetes, caper fruit extract (1,200 mg/day for 2 months) reduced blood levels of sugar and hemoglobin bound to sugar (HbA1c) without causing any adverse effects [39].

In several studies in diabetic rats and mice, caper fruit extracts lowered blood sugars without changing insulin levels [33, 40, 41, 42].

Diabetes may lead to a buildup of fatty molecules (triglycerides and cholesterol) in the blood. In diabetic rats, caper plant and fruit extract reduced blood and liver triglyceride and cholesterol levels. The plant extract also reduced the levels of LDL cholesterol and increased HDL, which helps balance overall fats in the blood [43, 40].

In diabetic rats, a caper fruit extract reduced kidney, liver, and pancreas damage [44].

2) Capers May Reduce Liver Damage

In a clinical trial on 44 people with non-alcoholic fatty liver disease, 40 – 50 g of caper berries per day for 12 weeks reduced disease severity and the levels of two important markers of liver damage – ALT and AST [45].

In another trial on 36 people with liver damage (cirrhosis), a herbal complex with 65 mg caper plant extract (3 tablets 3x/day) for 6 months reduced fluid buildup within the abdomen (ascites), ALT and AST levels [46].

An acid (draconic acid) from a caper plant extract reduced liver damage in rats and prevented liver cell death from various toxins [47].

In mice, high doses of a caper plant extract (400 mg/kg) and quercetin (20 mg/kg) reduced liver damage from toxins [26].

3) Capers May Reduce Inflammation

In two studies in mice, caper extracts (from aerial parts and buds) reduced the swelling caused by acute inflammation [48, 12+].

Caper fruit extracts relaxed the airways in rats, which may improve asthma [49].

Allergies

In a clinical trial on 8 healthy people, 100 mg of a gel with 2% caper bud extract prevented the skin inflammation triggered by histamine. Caper bud extracts also reduced airway inflammation and narrowing (bronchospasm) from allergens in Guinea pigs [50].

Arthritis

In two studies in arthritic rats, both caper fruit extract and a traditional Chinese medicine remedy based on capers reduced joint inflammation and pain [51, 29].

Arthritis causes inflammation in the joints, which progressively destroys their cartilage. In a study in cartilage cells exposed to an inflammatory protein (IL-1beta), caper bud extracts blocked the molecules that worsen inflammation in the long run (nitric oxide, mucopolysaccharides, prostaglandins, and free radicals) [52].

4) Capers May Protect the Skin

In a clinical trial on 6 healthy people, 100 mg caper bud extract prevented skin inflammation caused by UV light [53].

Several cosmetic products containing caper fruit extracts (e.g., Gatuline, Derma-Sensitive, SKIN MOON, SKIN SAVE) are marketed for their skin-protective, anti-aging, and anti-inflammatory benefits [3].

5) Capers May Prevent Alzheimer’s (in animals)

In rats with Alzheimer’s disease, caper fruit and bud extract blocked the production of two enzymes that trigger this disease and reduced cognitive damage [23, 54].

6) Capers May Prevent Cancer (in animals and cells)

Caper fruit extract (especially its carbohydrates and alkaloids) increased survival time in mice with cancer and killed liver and stomach cancer cells [32, 27, 55, 56].

Caper plant extract and essential oils blocked the master inflammatory pathway NF-kB and stopped colon cancer cells from dividing [30].

The digestion of red meat can trigger the production of harmful oxidant molecules that are needed to break down its fats. But the buildup of these substances may cause cancer and heart disease. In one study, caper bud extracts prevented the buildup of harmful breakdown products of red meat [57+].

7) Capers May Lower Blood Pressure (in animals)

In rats, caper fruit extract lowered blood pressure and increased the elimination of sodium, potassium, and chloride via urine. In tissue studies, it also relaxed the largest artery in the body, which the heart uses pump oxygen-rich blood to tissues [58, 59].

8) Capers May Help Lose Weight (in animals)

In obese mice fed a high-fat diet, caper fruit extract reduced body weight [34].

9) Capers May Improve Bone Regeneration (in animals)

In rats with damaged jaw bones, caper bud extract improved the formation of new bones and connective tissue. It increased the activity of cells that build and strengthen bones [60].

10) Capers May Reduce Infections (in cells)

In test tubes, caper fruit extract reduced the formation of biofilms and the release of bacterial toxins that may cause antibiotic-resistant infections (in E. coli, Pseudomonas aeruginosa, and other bacteria that cause urinary and lung infections) [61].

Caper plant extract completely prevented the growth of two fungi that cause ringworm (Microsporum canis and Trichophyton violaceum), a common skin infection in humans also known as tinea. It also blocked fungi that cause ringworm in pets [62].

In test tubes, caper plant extract killed the parasite that causes Chagas disease (Trypanosoma cruzi) and blocked those that cause sleeping sickness, malaria (Plasmodium falciparum), and leishmaniasis [63+].

In white blood cells (peripheral blood mononuclear cells), caper bud extract blocked the genital herpes virus [35].

Health Benefits of Other Caper Parts

Although this article focuses on the edible buds and fruits of the caper bush, the leaves, roots, and seeds may have different active compounds and other health benefits.

In fact, the leaves and roots have been traditionally used as natural remedies for several conditions. The leaves are mainly used for [3, 2+]:

  • Diabetes
  • The common cold
  • Headaches
  • Improving fertility in women
  • Fungal infections
  • Liver disorders
  • Joint diseases
  • Hemorrhoids

While the roots and root bark are used for [3, 2+]:

  • Skin diseases
  • The common cold
  • Liver, spleen, and kidney disorders
  • Constipation and stomach disorders
  • Rheumatism
  • Gout
  • Anemia
  • Swelling
  • Toothache

Active Compounds in Caper Leaves, Roots, and Seeds

Caper leaves have the same antioxidant compounds as the flower buds and fruits but their levels differ since leaves have:

  • Higher antioxidant phenols (especially rutin) [16+, 64]
  • More carotenoids [65]
  • Lower vitamin E content [65]

On the contrary, the volatile components in leaf essential oils differ Leaves don’t have a lot of the sulfur-rich isothiocyanates but contain aromatic compounds like carvone, and thymol, as well as palmitic acid [66+]:

Some of the main active compounds found in caper roots include [67, 68, 69]:

  • Alkaloids (like capparispine)
  • Betaines (like glycine betaine)
  • Isothiocyanates
  • Coumaric acid

The main components of caper seeds are [70, 71, 72, 73]:

  • Fatty acids (omega-6, oleic, omega-3, and palmitic acids)
  • Proteins
  • Fiber
  • Vitamin E
  • Sterols (sitosterol, campesterol, stigmasterol, brassicasterol)
  • Alcohols (octadecanol, citrostadienol)
  • Carotenoids
  • Glucosinolates (glucocapperin)

2) Health Benefits of Caper Leaves, Roots, and Seeds

Health Benefits of Caper Leaves (Extracts)

  • Reduced liver and kidney damage caused by toxins in rats [74].
  • Slowed down Alzheimer’s disease in rats [23].
  • Blocked the production of a Th17 immune protein (IL-17) and activated a Th2 one (IL-4) in white blood cells [75].
  • Increased the production of a protective pigment (melanin) in skin cells [76].
  • Blocked several bacteria that cause gut infections [77].

Health Benefits of Caper Roots

  • The root extract lowered blood sugar levels in rats [78].
  • Powdered roots and the extract reduced joint pain in arthritic rats [79].
  • The root extract blocked several infectious bacteria and fungi [80].

Health Benefits of Caper Seeds

  • The seed extract prevented cognitive damage in mice [28].
  • Two caper seed proteins blocked the division of HIV and breast, liver, and colon cancer cells [81, 82].

Side Effects

The most common side effect of eating capers is the irritation of the mouth lining due to the mustard oils (isothiocyanates) [83+].

Mustard oils also cause contact dermatitis in Guinea pigs, although this is rare in humans. There’s only one report of a person who applied wet minced caper compresses on the elbow and developed skin allergies [84+].

Some people are allergic to capers. One person developed an allergic reaction with redness, face and hand swelling, and hoarseness after eating caper berries [85+].

Capers are likely safe as food, but the toxicity of caper extracts has barely been investigated.

Only one study reported no side effects in people taking 1.2 g/day of a 24% fruit extract for 2 months. Until long-term toxicity studies of caper extracts are published, children, pregnant or breastfeeding women should stick to food sources and avoid capers extracts and supplements [39].

Caution

Due to their high sodium content, capers should be avoided by people on a low-sodium diet or with the following conditions:

  • High blood pressure
  • Water retention
  • Osteoporosis

This doesn’t apply to raw capers, or cooked fresh capers, which naturally contain very little salt.

Since capers may reduce blood sugar levels, diabetics who often eat capers should carefully monitor their blood sugar levels [36, 39].

Drug Interactions

Because capers lower blood sugar levels, they may increase the effect of insulin or oral antidiabetic drugs such as:

  • Chlorpropamide, Tolbutamide
  • Glimepiride, Glipizide, Glyburide
  • Pioglitazone, Rosiglitazone

Food & Supplements

Pickled or salted capers can be eaten as snacks, used as garnishing to dishes or included in many recipes of the Mediterranean cuisine [3].

The fruits, called caper berries, are also pickled and eaten as snacks. In Greece and Cyprus, the leaves are pickled or boiled and used in salads and fish dishes. They can also substitute for an animal enzyme (rennet) in cheese production [3, 2+].

Supplements with caper extract are also available as capsules to boost the immune system, reduce oxidative damage, protect the liver, and balance the use and breakdown of blood sugars and fats. Capers extracts are sometimes added to combination supplements, such as those for liver support.

Dosage

Information about the safest or most effective dosage of capers is limited.

The doses used in clinical trials were:

  • Type 2 diabetes: 3 capsules with 400 mg of 24% caper fruit extract daily for 2 months [39]
  • Non-alcoholic fatty liver disease: 40 – 50 g pickled caper berries per day for 2 weeks [45]
  • Liver damage (cirrhosis): 3 tablets of a complex with 65 mg caper extract 3x/day [46]
  • Skin inflammation: 100 mg of a gel with 2% caper bud extract [50, 53]

User Experiences

All consumers bought capers to prepare appetizers or various meals. They were generally satisfied and especially valued their taste, texture, and ease of use in salads and pasta.

However, their taste is not for everyone. A user considered them ‘revolting’ and some users complained that capers are too salty, even after rinsing. Other consumers liked the taste but were concerned about the high sodium content.

Similarly, most people buying caper berries to eat as snacks were satisfied with their taste, texture, and size. Depending on the brand, some users complained that the berries were too salty, too mushy, had too many seeds, or tasted too much like vinegar.

Limitations and Caveats

The main limitation is that very few benefits have been tested in humans. Only 5 clinical trials have been carried out, of which 2 had a very small sample size (<10 people) while the largest one included only 54 people. This may produce unreliable results and trials with larger populations are needed.

The role of capers in improving arthritis, preventing neurodegenerative diseases, preventing cancer, lowering blood pressure, helping lose weight, improving bone regeneration, and fighting infections have only been tested in animals and cells. Studies on humans are required to confirm these benefits.

The only clinical trial using caper berries also included some lifestyle changes guided by a nutritionist, which could have contributed to the observed effects on non-alcoholic fatty liver disease [45].

In some of the studies, the caper extract didn’t only include flower buds or fruits, but also the leaves. Because leaves have higher flavonoids, the effect may be stronger than that from eating capers [40, 46, 47, 26, 48, 86, 30, 62, 63].

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About the Author

Carlos Tello, PhD (Molecular Biology)

PhD (Molecular Biology)

Carlos received his PhD and MS from the Universidad de Sevilla.

Carlos spent 9 years in the laboratory investigating mineral transport in plants. He then started working as a freelancer, mainly in science writing, editing, and consulting. Carlos is passionate about learning the mechanisms behind biological processes and communicating science to both academic and non-academic audiences. He strongly believes that scientific literacy is crucial to maintain a healthy lifestyle and avoid falling for scams.

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