University of Florida: the anti-inflammatory power of red grapes, here's how it works

IN BRIEF

• Resveratrol is a polyphenol found mainly in the skin of red grapes, but also in peanuts and some berries; concentrations in foods are variable. [1]
• Molecular studies indicate that resveratrol can modulate the inflammatory response through the estrogen receptor (ERα) and other intracellular pathways, reducing the expression of certain inflammatory mediators such as IL-6. [3][5]
• The oral bioavailability of resveratrol is low: the molecule is rapidly metabolized, and the amount of free compound reaching systemic circulation is limited. [2]
• Clinical trials and meta-analyses show conflicting results: some studies report modest effects on inflammation and cardiovascular parameters, while others find no clear benefits; the quality and heterogeneity of studies are critical factors. [6][7][8]

Abstract: what does science say?

Resveratrol is a natural compound that acts on multiple cellular targets: it can selectively modulate estrogen receptor (ERα) signaling, influence pathways related to oxidative stress regulation and sirtuin activity, and reduce the production of certain inflammatory cytokines such as interleukin-6. These actions have been observed in laboratory experiments and preclinical models; in clinical studies, the effects are more nuanced and depend on dose, duration, studied population, and administration form. Oral bioavailability is a known limitation, and current evidence does not allow attributing a universal protective effect to habitual wine consumption or supplements. The data support biological plausibility but not consolidated causal proof for widespread benefits in the general population.

What is resveratrol and where is it found?

Resveratrol is a polyphenol belonging to the stilbene class. In nature, it forms in plants as a response to environmental stress (infections, damage, UV rays). The most well-known food sources are red grape skin and derived products (juice and wine), but it is also found in peanuts, pistachios, some berries (blueberries, blackberries, raspberries), and in plant extracts used in supplements. Concentrations in individual matrices vary greatly depending on the species, cultivar, agricultural practices, and processing methods: for example, grape skin and certain Polygonum species (knotweed) can contain higher quantities than the grape pulp.

From a practical point of view, it is important to remember that the mere presence of the compound in a food does not guarantee a measurable biological effect in the human body: quantity, chemical form, consumption method, and interactions with other food constituents all contribute to determining actual exposure. [1]

Bioavailability and form of intake

One of the main limitations to the use of resveratrol is its low bioavailability after oral intake. Pharmacokinetic studies in healthy volunteers have shown that, despite often high intestinal absorption, the fraction of free molecule that remains unchanged in plasma is very small due to rapid conjugation reactions (glucuronidation and sulfation) at the intestinal and hepatic level. This means that the administered dose does not automatically translate into sustained concentrations of the active form in systemic circulation. [2]

For this reason, pharmacological research has explored alternative formulations (micronization, nanoparticle delivery, transdermal or sublingual administration) and chemical analogs that can maintain biological activity with better stability and availability. However, the clinical efficacy evidence for these solutions is still limited and inconsistent. [2][11]

Main molecular mechanisms

Resveratrol shows a multi-target profile: it acts as a modulator of nuclear receptors, transcriptional factors, and metabolic pathways involved in cellular homeostasis and the inflammatory response. It is useful to distinguish effects observed in cellular or animal models from evidence obtained in humans.

Resveratrol and estrogen receptor (ERα)

Structural and functional research conducted by laboratory groups linked to the original study has shown that resveratrol binds to estrogen receptor α (ERα) and acts as a "signal-selective" ligand: it can modulate gene expressions related to inflammation without fully activating the cell proliferation programs typical of a strong estrogenic stimulus. This mechanism partly explains why the compound can reduce the expression of pro-inflammatory mediators such as IL-6 in some experimental models. Such data offer biological plausibility for anti-inflammatory effects but do not replace direct evidence of generalizable clinical benefit. [3]

SIRT1, oxidative stress, and antioxidant pathways

Among the molecular targets of resveratrol, the activation of sirtuins, a family of deacetylases linked to metabolism regulation and stress response, has also been proposed. Research on simple organisms has shown that resveratrol can stimulate activities similar to those of caloric restriction and influence cell survival pathways; however, the transfer of these results to the human context is complex and mediated by numerous variables. This line of research contributes to explaining the possible antioxidant and metabolic effects observed in preclinical experiments. [5]

What clinical evidence says about inflammation and cardiovascular risk

In recent years, several systematic reviews and meta-analyses of clinical trials have evaluated the effect of resveratrol supplementation on inflammatory biomarkers (e.g., CRP, TNF-α, IL-6) and cardiovascular parameters (blood pressure, lipid profile). The results are not unequivocal: some analyses document a modest reduction in certain inflammatory markers or some blood pressure parameters in selected subgroups or at high doses, while others find no clinically relevant effects in the general population. [6][7]

Differences between studies depend on many causes: studied populations (healthy individuals vs. patients with cardiovascular disease or diabetes), dose and purity of the compound, duration of intervention, measured endpoints, and methodological quality of the trials. For these reasons, guidelines do not have widespread recommendations for the routine use of resveratrol as a preventive or therapeutic strategy. [8][9]

What it means in practice

For the general public, the practical message is clear but cautious: the consumption of fresh grapes, berries, and nuts as part of a balanced diet contributes to the intake of molecules with antioxidant action, including resveratrol. However, studies do not support the use of red wine as a recommended means to obtain benefits from resveratrol, especially due to the alcohol content which nullifies or reduces potential benefits in many health conditions.

The intake of resveratrol-based supplements shows heterogeneous results and, at times, modest effects on biological markers. If considering the use of supplements, it is advisable to discuss it with a doctor, taking into account any medications being used (possible interactions) and the quality of the preparation. [2][8]

KEY POINTS TO REMEMBER

• Resveratrol has plausible molecular mechanisms for anti-inflammatory and metabolic action, including interference with ERα and alterations of intracellular pathways. [3][5]
• Oral bioavailability is low: most of the compound is rapidly converted into metabolites. This limits the impact of a single dose. [2]
• Clinical evidence is conflicting: some meta-analyses document modest effects on specific biomarkers or in specific populations; others find no consistent benefits. [6][7][8]
• Consuming polyphenol-rich foods as part of a varied diet is reasonable; the use of supplements requires individual clinical evaluation. [1][8]

Limitations of the evidence

It is fundamental to distinguish between study types. Molecular and preclinical data (cells, animals) show potential mechanisms but do not automatically establish clinical effects in humans. Observational studies can highlight associations (e.g., correlation between inflammatory biomarkers and outcomes) but do not prove causality. Randomized clinical trials represent the gold standard, but many trials on resveratrol are small, short-term, or present heterogeneity in dosages and formulations: this complicates aggregated interpretation.

Other important limitations include the heterogeneity of populations (healthy vs. sick), variability in the composition of commercial supplements, and limited knowledge of interactions with drugs and long-term effects. For these reasons, results must be interpreted with caution, and more robust and standardized clinical studies are needed. [8]

Editorial conclusion

Resveratrol remains a compound of great scientific interest: it has biological mechanisms consistent with anti-inflammatory and metabolic effects and represents a model for the development of more effective and bioavailable molecules. However, its translation into clinical recommendations or generalized health messages is not supported by solid and uniform evidence. The most prudent choice for the general population is to favor a diet rich in plant-based foods, limit alcohol consumption, and consult a doctor before using resveratrol-based supplements, especially in the presence of existing conditions or ongoing pharmacological therapies.

Editorial note

Article: originally published in the past and updated according to scientific and divulgative criteria. The text is for informational purposes only and does not replace the advice of a treating physician. For diagnostic or therapeutic decisions, consult healthcare professionals.

SCIENTIFIC RESEARCH

1. Nwachukwu JC, Srinivasan S, Bruno NE, et al. Resveratrol modulates the inflammatory response via an estrogen receptor‑signal integration network. eLife. 2014;3:e02057. https://doi.org/10.7554/eLife.02057.[3]
2. Walle T, Hsieh F, DeLegge MH, Oatis JE Jr, Walle UK. High absorption but very low bioavailability of oral resveratrol in humans. Drug Metab Dispos. 2004;32(12):1377–1382. https://doi.org/10.1124/dmd.104.000885.[2]
3. Khattar S, Khan SA, Zaidi SA, et al. Resveratrol from Dietary Supplement to a Drug Candidate: An Assessment of Potential. Pharmaceuticals (Basel). 2022;15(8):957. https://doi.org/10.3390/ph15080957.[1]
4. Lin SC, Gan ZH, Han K, et al. Interleukin‑6 as a prognostic marker for breast cancer: a meta‑analysis. Tumori. 2015;101(5):535‑541. https://doi.org/10.5301/tj.5000357.[4]
5. Howitz KT, Bitterman KJ, Cohen HY, et al. Small molecule activators of sirtuins extend Saccharomyces cerevisiae lifespan. Nature. 2003;425:191–196. https://doi.org/10.1038/nature01960.[5]
6. Sahebkar A, Pasdar A, Salimzadeh L, et al. Effect of resveratrol on inflammatory cytokines: A meta‑analysis of randomized controlled trials. Eur J Pharmacol. 2021;908:174380. https://doi.org/10.1016/j.ejphar.2021.174380.[6]
7. Zhang Z, Liu Y, Zhang X, et al. Effect of resveratrol on blood pressure: a meta‑analysis of randomized controlled trials. Clin Nutr. 2015;34(1):27–34. https://doi.org/10.1016/j.clnu.2014.03.009.[7]
8. Singh AP, Singh R, Verma SS, et al. Health benefits of resveratrol: Evidence from clinical studies. Med Res Rev. 2019;39(5):1851–1891. https://doi.org/10.1002/med.21565.[8]
9. Anti‑inflammatory effects of resveratrol in patients with cardiovascular disease: a systematic review and meta‑analysis of randomized controlled trials. Complement Ther Med. 2022;70:102863. https://doi.org/10.1016/j.ctim.2022.102863.[9]