Supplements
Quercetin: What It Does, and What to Measure
Reviewed by a qualified clinician · analysed at UKAS-accredited UK labs (ISO 15189)
Last reviewed July 20267 min read
Every Helvy guide is written by our health editors, then checked by a qualified clinician before it goes live and re-checked as the science moves. We name clinical roles, not individuals, until each reviewer has agreed to be credited publicly. This is wellness guidance to help you understand your own data, not a diagnosis.
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Quercetin is a plant compound found in onions, apples and tea. Pooled trials show a small average fall in blood pressure, near 2 mmHg. Its effect on inflammation markers is inconsistent. No quercetin health claim is authorised in Great Britain. Measuring hs-CRP and your lipids shows whether inflammation is your real problem.
Want your baseline first? Build your test →As of July 2026. Quercetin is having a good year in UK search. Buyer guides and supplement forums now pitch it for inflammation, blood pressure and hay fever. The pooled human evidence is more modest than the marketing. Here is what the trials found, and what to read on a blood test instead of guessing.
1. What is quercetin?
Quercetin is a flavonol, one of the plant compounds that give fruit and vegetables their colour. You already eat it every day. Onions are the richest common source, followed by lettuce, asparagus, peppers, apples and tea.
The gap between food and capsule is the thing to understand first. Population studies put typical daily intake at roughly 16 to 25 mg. A UK supplement delivers 250 to 500 mg per capsule. That is ten to thirty times a normal day’s intake from food.
That gap matters. When researchers followed 15,662 adults for three years, quercetin from food showed no link to new high blood pressure. The authors were blunt about why. Diet alone does not reach a dose that moves the number.
2. Does quercetin lower blood pressure?
A little, on average, at supplement doses. The effect shrinks as the quality of the evidence rises, which is the pattern worth knowing.
The most quoted analysis is from 2016, in the Journal of the American Heart Association. It pooled seven trials and 587 people. Systolic pressure fell by 3.04 mmHg and diastolic by 2.63 mmHg.
A 2023 umbrella review then pooled the pooled studies. It is the highest tier of evidence we have. Systolic pressure fell by 1.9 mmHg. Diastolic pressure did not move at all. The authors graded their own certainty as very low to moderate, and the trials disagreed with each other a great deal.
Read that honestly and it is a real but small signal. For context, the NHS lists diet, exercise, weight and salt as the levers that move blood pressure. A supplement worth around 2 mmHg sits well behind those.
3. Does quercetin lower inflammation?
This is the main reason people buy it, and the answer is genuinely unsettled.
One 2017 review found a small drop in CRP, the main blood marker of inflammation, of 0.33 mg/L. A 2020 review found no overall effect on CRP at all, nor on the messengers IL-6 and TNF-alpha. The 2023 umbrella review found no effect on inflammation either. TNF-alpha has come back flat in every analysis that tested it.
So quercetin does not reliably lower inflammation markers in people. Which raises the more useful question. Is your inflammation actually raised in the first place?
“Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are blood tests that can be used to check the levels of inflammation in your body.”
— the NHS, on the blood tests used to check inflammation
Most people taking quercetin for inflammation have never seen their own number. It is a guess dressed up as a plan.
4. What is worth measuring before you start?
Four readings turn a hunch into something you can judge.
- hs-CRP. The high-sensitivity version of CRP reads the low band a standard test cannot resolve. Under 1.0 mg/L is the performance range, 1.0 to 3.0 mg/L the middle, above 3.0 mg/L the higher band.
- Your lipids. If heart risk is the worry behind the supplement, the cholesterol panel answers it far more directly than quercetin does.
- HbA1c. Your average blood sugar over three months. It sits alongside inflammation in the same risk picture.
- Cortisol. Worth a look if the real complaint is feeling run down rather than inflamed.
Read them before you start, then again around twelve weeks in. Two readings are what tell you whether anything changed. Our inflammation testing guide covers the wider picture, and the heart health hub pulls the risk markers together.
5. Why do UK quercetin labels stay so vague?
Because the law gives them nothing to say. This is the part of the story the buyer guides skip.
Great Britain keeps a register of health claims a food or supplement is allowed to make. Quercetin appears in it five times. Every entry is non-authorised. Not one quercetin claim is permitted.
The oxidative damage claim was assessed on the evidence and failed. The scientific opinion behind the register put it plainly: “a cause and effect relationship has not been established between the consumption of quercetin and protection of DNA, proteins or lipids from oxidative damage.” Three further claims, on the heart, the brain and the liver, were rejected as too vague to even assess.
This explains a pattern you can see on any shelf. Most UK quercetin products are sold blended with vitamin C, zinc or bromelain. Those nutrients do carry authorised claims. The wording on the box is usually hanging off the vitamin, not the quercetin.
6. What dose do people take, and is it safe?
UK products run from 250 to 500 mg per capsule, and most labels direct 500 to 1,000 mg a day. Check the panel rather than the front of the box. Several brands print 500 mg large, then state it per two capsules.
Form matters more than the milligrams suggest. A 2025 review of 31 human studies found the plain quercetin used in most capsules is absorbed around twenty times less well than the form you get from onions. Adding fat or fibre to the meal roughly doubles absorption. So 500 mg on a label is not 500 mg delivered.
On safety, a 2018 review by German federal risk assessors found side effects were rarely reported in trials and mild when they appeared. The same review flagged the honest limit of the evidence. There is no adequate safety data for doses of 1,000 mg or more taken beyond twelve weeks. It also advised caution for anyone with existing kidney damage.
Quercetin can also change how your body handles medicines. In one human study, 1,500 mg a day for a week raised blood levels of the antihistamine fexofenadine by 55 per cent. If you take any regular medication, ask a pharmacist before adding it.
7. Which blood test covers the quercetin checklist?
Helvy’s Advanced Heart Health panel (£159) is the closer match. It reads hs-CRP, HbA1c, the full lipid picture, ApoB and Lp(a) from one home sample. That covers both questions quercetin is usually bought to answer.
If the complaint is more “run down” than “heart risk”, the General Energy & Wellness panel (£149) reads standard CRP alongside cortisol, thyroid, vitamin D and B12. Note that it uses standard CRP, not the high-sensitivity version. Prefer to choose your own markers? The build-my-test tool lets you do exactly that.
READY TO TEST?
Stop guessing at inflammation. Read it.
Helvy’s home blood tests read hs-CRP, your lipids and HbA1c with clear context, so you can see whether a supplement is answering a real need. Results in around five working days from UKAS-accredited UK labs.
Frequently asked questions
What is quercetin good for?
The best evidence is a small average fall in blood pressure of roughly 2 mmHg at supplement doses. Results on inflammation markers are inconsistent. No quercetin health claim is authorised in Great Britain, so no UK product is allowed to promise you a benefit.
Does quercetin lower CRP?
Not reliably. One 2017 review found a small drop of 0.33 mg/L. A 2020 review found no overall effect, and a 2023 umbrella review found none either. Reading your own hs-CRP before and after twelve weeks is the only way to know what happened in your case.
Does quercetin help hay fever?
The mast cell mechanism people cite comes almost entirely from animal and laboratory work. Human trials are few and small, and reviewers rate the certainty as low to very low. Treat it as unproven rather than established.
How much quercetin is in food?
Typical daily intake sits at roughly 16 to 25 mg, mostly from onions, tea, apples and salad leaves. A capsule holds 250 to 500 mg. At food levels, one study of 15,662 adults found no link to blood pressure.
Is quercetin safe to take daily?
Trials report side effects rarely, and mild ones when they occur. There is no adequate safety data above 1,000 mg a day past twelve weeks. Anyone with kidney problems, or on regular medication, should speak to a pharmacist or GP first.
Which blood test should I do before taking quercetin?
A sensible baseline is hs-CRP, your lipids and HbA1c. Helvy’s Advanced Heart Health panel reads all three. This guide is general information, not medical advice.
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