Resveratrol

What it is

Resveratrol is a polyphenol found in the skins of red grapes, berries and peanuts. Supplements usually come from Japanese knotweed rather than wine.

It became famous in the 2000s after animal studies suggested it mimicked some effects of calorie restriction. Human trials have been far less impressive.

It is sold in the UK as a food supplement, often at doses far higher than you could get from drinking wine.

How it works

In lab work, resveratrol activates enzymes called sirtuins and affects pathways linked to inflammation and energy metabolism. In people, it is rapidly metabolised and has low bioavailability, so how much reaches tissues in active form is uncertain.

What the evidence says

• Limited Blood sugar control in type 2 diabetes
  Some trials show modest improvements, others none; it should not replace prescribed treatment.
• Limited Blood pressure
  Meta-analyses suggest a small effect at higher doses, with inconsistent findings.
• Weak Cholesterol and heart markers
  Results are mixed and generally small.
• Weak Lifespan or healthy ageing
  Animal findings have not been convincingly reproduced in humans.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Typical supplement doses are 100-500 mg daily.
• Take with food, ideally including fat, to help absorption.
• Studies use higher doses (up to 1 g or more) for short periods, but side effects rise with dose.
• No official recommended intake; check current guidance and the label.

Forms and what to look for

• Trans-resveratrol is the active form; check the label specifies it.
• Japanese knotweed (Polygonum cuspidatum) extract is the usual source; it can also contain emodin, a laxative compound.
• Micronised or liposomal products claim better absorption; evidence of real benefit is limited.
• Red wine extract products usually contain much less resveratrol per capsule.

What to expect, and when

• Studies run 8-24 weeks or longer for measurable changes.
• Most healthy people will not feel anything.
• Any change in markers should be measured by blood tests rather than by feel.

Side effects

• Nausea, diarrhoea or stomach cramps, especially at higher doses.
• Headache or dizziness.
• Joint or muscle pain reported in some trials.
• Skin rash in sensitive individuals.

Interactions

• Blood thinners (warfarin, aspirin, clopidogrel): resveratrol may add to the bleeding risk.
• Drugs processed by liver enzymes (CYP3A4, CYP2C9): resveratrol may alter levels; check with a pharmacist.
• Hormone-sensitive conditions: it has weak oestrogen-like activity in lab studies.
• Diabetes medicines: may add to blood sugar lowering.

Who should avoid it

• People on anticoagulants or antiplatelet drugs unless a clinician agrees.
• Pregnant or breastfeeding women.
• People with hormone-sensitive cancers or conditions, until discussed with a doctor.
• People due to have surgery; stop in advance as advised by the surgical team.

Risks and safety

• High doses (2 g and above) in trials caused more digestive side effects, and some kidney concerns were reported in a myeloma trial.
• Knotweed-based products may contain other active compounds.
• Long-term safety at high doses is unknown.
• Quality varies widely between brands.

Buying well: quality and testing

• Look for products stating trans-resveratrol content and extract source.
• Choose third-party tested brands.
• Avoid labels promising to "reverse ageing".
• Check serving size, as capsules often contain far less than the front label suggests.

Bottom line

Resveratrol is a classic case of strong early excitement followed by underwhelming human evidence. It is generally safe at moderate doses but may interact with blood thinners and other drugs. It might suit curious people with realistic expectations; it is not a replacement for a good diet or medicines.