Resveratrol benefits

How is resveratrol’s effect in the cell separated from the benefit of the supplement?

Many effects of resveratrol have been reported in cell and animal experiments; for example, it increased survival in mice fed a high-calorie diet. ^[6] In humans, at least 70% of a 25 mg oral dose is absorbed, but unchanged resveratrol in plasma is in trace amounts; most of it circulates as sulfate and glucuronide compounds. ^[5] For this reason, an effect in a cell experiment does not mean the supplement will have the same effect in humans; for each claim, human studies must be examined.

Does resveratrol lower blood sugar?

The 2021 umbrella review, which examined 11 meta-analyses in type 2 diabetes (1,476 people, 29 outcomes), stated that some beneficial effects were reported on glycemic control and insulin resistance, but that in nearly all outcomes the effect size was trivial, the certainty of evidence was very low to low, or the number of trials was small. For HbA1c, a clinically important effect of moderate certainty was seen in the short term (less than 12 weeks): mean difference −1.05% (95% CI −2.09% to −0.02%; 6 trials). ^[1]

Limits: the upper bound of the confidence interval nearly touches zero; the trials are short and small. The review authors concluded that under these conditions the supplement is not supported for cardiometabolic risk markers. ^[1] Evidence grade: C.

Does resveratrol lower blood pressure?

The 2015 meta-analysis by Liu and colleagues had 6 trials (247 people in total). Overall result: resveratrol did not significantly lower systolic and diastolic blood pressure. In a prespecified subgroup analysis, intake of 150 mg per day and above lowered systolic blood pressure by −11.90 mmHg (95% CI −20.99 to −2.81); there was no significant reduction at low doses, and meta-regression did not show a dose–effect relationship. ^[2]

The subgroup finding is not the main result; the wide confidence interval also shows the uncertainty. In addition, the result covers trials published up to 2014. Evidence grade: D.

Is resveratrol good for postmenopausal bone density?

RESHAW is a 24-month, double-blind, two-period crossover RCT comparing 75 mg of resveratrol twice daily with placebo in postmenopausal women. Participants were women aged 45–85 who were at least 12 months after menopause and not receiving hormone replacement therapy; people using insulin or warfarin and those with a history of breast or cervical cancer were excluded. ^[3]

With 12 months of supplementation, compared with placebo, bone density increased in the lumbar spine (+0.016 g/cm²) and femoral neck (+0.005 g/cm²), and the bone resorption marker CTX decreased by 7.24%. The authors reported a reduction in the calculated 10-year probability of fracture risk. In a sub-analysis the benefit was larger in participants who also took vitamin D and calcium supplements. 125 women completed the trial. A company that is a resveratrol manufacturer supplied the capsules and additional funding (according to the authors the company had no role in design, analysis and writing); the authors declared no conflict of interest. ^[3]

Limits: fracture outcome was not measured, the increases in bone density are small, the trial covers a single group of women and is a single trial. Evidence grade: C.

Does resveratrol protect the heart or extend life?

No benefit has been shown in humans. In the InCHIANTI cohort of 783 people aged 65 and over, 24-hour urine metabolites, the marker of dietary resveratrol, did not predict mortality risk, inflammation markers, cardiovascular disease and cancer over 9 years of follow-up; the hazard ratio for death (comparison of the lowest and highest quartiles) was 0.80 (95% CI 0.54–1.17). ^[4] This is an observational study and covers dietary levels (such as wine, grapes), not supplement doses.

Increased survival has been reported in mice fed a high-calorie diet; this finding belongs to an animal model. ^[6] The blood pressure and blood sugar meta-analyses examined risk markers, not cardiovascular events. ^{[2] [1]} Evidence grade: E (no benefit shown).

Does resveratrol help with weight loss and fatty liver?

The umbrella review stated that beneficial effects were reported for waist circumference in metabolic syndrome and for body weight and inflammation markers in fatty liver, but that in nearly all outcomes the effect size was trivial, the certainty of evidence very low to low, or the number of trials small. ^[1] It cannot be said to be supported for weight loss. Evidence grade: D.

Why do studies give different results?

Studies differ in the dose and participants they used: in RESHAW, 75 mg twice daily was given; the significant subgroup in the blood pressure meta-analysis covered doses of 150 mg per day and above. ^{[3] [2]} Because absorption of oral resveratrol is high and bioavailability very low, whether the effective level in blood is proportional to dose is uncertain; in the Liu meta-analysis as well, meta-regression did not show a dose–effect relationship. ^{[5] [2]} For this reason, it cannot be assumed that an effect seen in one study will be repeated at another dose, formulation or group.

Summary table