Small ingredients can add flavour and interesting plant compounds to our meals. Capers are a particularly rich source of quercetin—but what does that mean for our health?
When we think about nutritious food, we often imagine a large bowl of vegetables. Sometimes, however, an interesting ingredient comes in a very small jar. Capers are one example: sharp, salty and full of flavour, they also contain substantial amounts of a plant compound called quercetin.
What is quercetin?
Quercetin is a flavonol, part of the larger flavonoid family of plant compounds. It occurs in foods including onions, apples and berries. Scientists investigate its effects on oxidative stress, inflammation and cell signalling. [1, 2]
It is not a vitamin, and there is no established daily requirement. Calling it an antioxidant does not mean that eating it automatically prevents disease. The effects observed in laboratory experiments must be distinguished from benefits demonstrated in people.
Capers: a concentrated food source
The USDA flavonoid database lists mean quercetin values of approximately 173 mg per 100 g for canned capers and 234 mg per 100 g for raw capers. These are database averages, not a guarantee for every jar. Variety and processing affect the amount. [1]
Using the canned-caper average, a 10 g portion would provide approximately 17 mg of quercetin. This is a useful food-composition estimate, not the amount necessarily absorbed by the body. Nor is it a recommended medical dose.
You do not need to eat 100 g of capers to enjoy them. Think of them as a flavourful addition to a meal rather than the meal itself.
Capers also contain another flavonol, kaempferol. Like other plant foods, they provide a mixture of compounds; their appeal should not be reduced to one chemical. [1]
What benefits have been studied?
Blood pressure
A 2022 meta-analysis combined ten supplementation trials involving 841 participants. It found an average reduction in systolic blood pressure of about 2.4 mmHg across the mixed study population. This is a modest effect, and the trials tested supplements rather than ordinary servings of capers. [3]
A separate trial involving 70 adults tested 162 mg of quercetin daily from onion-skin extract for six weeks. There was no significant blood-pressure improvement across the whole group, although a subgroup with hypertension showed a reduction in 24-hour systolic pressure. [4]
These findings explain the scientific interest. They do not establish that capers treat high blood pressure or replace prescribed medicine.
Inflammation and allergies
Laboratory studies suggest that quercetin can influence inflammatory processes, including histamine release. That provides a reason to investigate it, but does not establish capers as an allergy treatment or a reliable alternative to an antihistamine. [2]
Healthy aging
There is no established evidence that eating capers or taking quercetin alone extends human life. Similarly, laboratory anticancer activity should not be presented as proof that a food or supplement treats cancer. [2]
A varied diet can include quercetin-rich foods without requiring us to promise more than the evidence shows.
Other foods to include
| Food | An easy way to use it |
|---|---|
| Onions, including red onions | Add to salads, lentils, soups or cooked vegetables. |
| Apples | Enjoy the washed fruit with its edible skin. |
| Berries | Add to oats or unsweetened yogurt. |
| Fresh dill | Use with potatoes, salads or a lemon dressing. |
| Capers | Add a small quantity to sauces, beans or vegetable dishes. |
Different foods contribute different plant compounds. There is little reason to organise an entire diet around maximising just one.
Bringing capers into the kitchen
Their sharp flavour works particularly well with:
- Lentil or chickpea salads with red onion and lemon.
- Pasta puttanesca: capers with tomatoes, olives, garlic and chilli. Many versions include anchovies; for a plant-based version, leave them out and let the capers and olives provide the savoury flavour. Whole-grain pasta is another option.
- Roasted cauliflower with parsley and olive oil.
- A tofu spread with lemon, herbs and chopped capers.
- A potato salad with dill and a mustard dressing.
For a simple dressing, combine chopped capers, lemon juice, a little olive oil and fresh herbs. Taste before adding salt: the capers may already provide enough.
Jarred capers are commonly preserved in salty brine or packed in salt. Drain and rinse them to remove surface salt, and check the sodium information on the label. Rinsing does not make them salt-free. If you have been advised to restrict sodium, portion size still matters.
Add them near the end of cooking when you want to preserve their distinctive texture and flavour. They can also be used directly in cold dishes according to the jar's instructions. There is no need for elaborate preparation to “activate” quercetin.
Food and supplements are different choices
A spoonful of capers is not equivalent to a concentrated quercetin supplement. Supplement formulations and doses vary, and quercetin can affect drug-metabolising enzymes in laboratory studies. The clinical importance of some proposed interactions remains uncertain. Memorial Sloan Kettering also notes possible interference with certain chemotherapy drugs. [2]
Before starting a supplement, ask your pharmacist or healthcare practitioner, particularly if you take regular medication or receive cancer treatment. Do not change prescribed treatment because of a food article.
The onion-extract research also does not mean that readers need to eat papery onion skins or make concentrated homemade extracts. Ordinary edible onions are a simpler kitchen choice.
The HealthyRetired approach
Dr Michael Greger's NutritionFacts.org includes a quercetin topic page with related nutrition research. It is useful further reading alongside the food-composition data and human trials cited here. [5]
For everyday eating, capers are worth considering because they bring flavour and quercetin to an otherwise ordinary meal. Enjoy them with vegetables, legumes and other whole foods, while keeping their salt content in mind.
Small jar, big flavour. No miracle required.
Sources and further reading
- USDA Database for the Flavonoid Content of Selected Foods, Release 3.1. Food-composition values, including capers and dill; figures are mg per 100 g edible portion.
- Memorial Sloan Kettering Cancer Center: Quercetin. Research background and supplement precautions.
- The effects of quercetin supplementation on blood pressure: meta-analysis (2022).
- Quercetin-rich onion-skin extract and ambulatory blood pressure: randomized crossover trial (2015).
- Dr Michael Greger, NutritionFacts.org: Quercetin.
Suggested picture: a small bowl of drained capers beside red onion, lemon and fresh dill. Alt text: “Capers with red onion, lemon and dill, ready to add to a meal.”