Apple polyphenols, blood sugar and uric acid in overweight adults
What it found
In overweight adults with slightly raised fasting blood sugar, 8 weeks of apple polyphenols lowered fasting glucose, uric acid and improved endothelial reactivity compared with placebo.
Lab tests in human cells suggest the extract blocks xanthine oxidase, the enzyme that makes uric acid.
What they found
Studies in people
Blood sugar
After 4 weeks, fasting plasma glucose fell by 6.1% in the apple polyphenol group. After 8 weeks it fell by 10.3% compared with the start and was lower than in the placebo group.
Uric acid
After 8 weeks, uric acid fell by 14.0% in the apple polyphenol group compared with the start and was lower than in the placebo group.
Blood vessel function
Endothelial reactivity improved in the apple polyphenol group compared with the start and with the placebo group. The improvement was proportional to the fall in uric acid.
Other measures
No significant changes were seen in blood pressure, arterial stiffness, cholesterol, triglycerides, liver enzymes or weight in either group.
Tolerability
No patient reported any side effect, and the apple polyphenol treatment was as well tolerated as the placebo.
Animal and lab studies
Lab tests on cells
In human umbilical vein endothelial cells, apple polyphenols blocked xanthine oxidase activity and reduced uric acid production. The amount needed to block half the enzyme was 130 ng/mL for enzyme activity and 154 ng/mL for uric acid production.
What the authors conclude
“In conclusion, apples polyphenols are strong xanthine oxidase inhibitors in vitro and exert a mild but significant SUA lowering effect in humans.”
Also in their conclusions
- They conclude that apple polyphenols are strong xanthine oxidase inhibitors in the lab and have a mild but significant uric acid lowering effect in people.
- They say this effect, together with the fall in fasting glucose, is probably the cause of the improved endothelial reactivity seen in the study.
- They suggest that if confirmed in larger trials, apple polyphenols could be useful for managing metabolic syndrome.
How it was done
The authors wanted to see whether apple polyphenols could lower uric acid by blocking xanthine oxidase, and whether a daily supplement would affect uric acid and blood vessel function in overweight people with slightly raised blood sugar.
They first tested apple polyphenols in human umbilical vein endothelial cells and compared the effect with allopurinol. Then they ran a randomised, double-blind, placebo-controlled trial in 62 overweight volunteers aged 18 to 70 with fasting plasma glucose between 100 and 125 mg/dL, who took 300 mg apple polyphenols or placebo daily for 8 weeks.
What it can’t tell you
- The trial lasted only 8 weeks, so it cannot show what happens over longer periods.
- The study was small, with 53 people completing it, so the results need confirmation in larger trials.
- The participants did not have gout or very high uric acid, so the findings may not apply to people with those conditions.
Who paid
- Authors work at
- Alma Mater Studiorum University of Bologna, Italy; University of Bologna, Italy
The paper
- Title
- Effect of apple polyphenols on vascular oxidative stress and endothelium function: a translational study
- Type
- Randomised controlled trial
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Cicero AFG, Caliceti C, Fogacci F, et al (2017). Effect of apple polyphenols on vascular oxidative stress and endothelium function: a translational study. Molecular nutrition & food research. doi:10.1002/mnfr.201700373Free full textPubMed 28755406DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error