Apple polyphenols have various potential health benefits. Because most of them are found in the peel, it’s easier to obtain these benefits by eating apples unpeeled. Continue reading to know the various health benefits of these dietary polyphenols.
What Are Apple Polyphenols?
Polyphenols are organic compounds found in fruits and vegetables. These secondary plant metabolites can be categorized as flavonoids and non-flavonoids. Apple polyphenols exert their potential health benefits through their antioxidant and anti-inflammatory activities. Although they are also found in the apple flesh, the highest polyphenol content is found in the apple peel.
Snapshot
Proponents
- Antioxidant and anti-inflammatory activity
- May help with blood sugar control
- May lower blood fat levels
- May improve physical performance
Skeptics
- Insufficient evidence for all benefits
Health Benefits
Insufficient Evidence
1) Antioxidant and Anti-Inflammatory
In a clinical trial on 62 overweight people, apple polyphenol extract reduced oxidative damage to the blood vessels In test tubes, they inhibited an enzyme that produces free radicals (xanthine oxidase) [1].
In another trial on 12 healthy nonsmokers, consuming apple juice improved blood antioxidant status. However, the rise in blood uric acid rather than in its polyphenols such as quercetin was associated with this effect [2].
The antioxidant and anti-inflammatory effects of apple polyphenols improved joint mobility and antioxidant status while reducing inflammation in a small trial on 12 healthy people given dry apple peel powder (4.25 g/day for 12 weeks) [3].
The combination of apple polyphenols and vitamin C improved antioxidant status (higher antioxidant activity and lower ICAM-1 and VCAM-1 levels) in another trial on 20 healthy people [4].
In rats, apple polyphenols suppressed pro-inflammatory cytokines and improved their antioxidant status [5].
Taken together, 4 small clinical trials (one of them with negative results) cannot be considered sufficient evidence that apple polyphenols have noticeable antioxidant and anti-inflammatory effects in humans. Larger, more robust clinical trials are needed to validate these preliminary findings.
2) Blood Sugar Control
In a clinical trial on 25 healthy people, a polyphenol-rich apple and blackcurrant drink reduced blood sugar levels after meals [6].
In another trial on 62 overweight people, apple polyphenol extract reduced fasting blood sugar [1].
The long-term administration of apple polyphenols (600 mg/day for 12 weeks) reduced sugar spikes after meals in a clinical trial on 65 people at risk of developing type 2 diabetes (impaired glucose tolerance) [7].
Apple polyphenols also increased insulin sensitivity in rats [8].
Although the results are promising, the evidence to support this potential health benefit comes from 3 clinical trials and a study in rats. Further clinical research is required to confirm them.
3) Physical Performance
In a clinical trial on 48 physically active men, taking 500 mg apple polyphenols the preceding evening and 1 hour before a high-endurance aerobic test extended the maximal performance time and delayed fatigue perception [9].
In rats, dietary apple polyphenols improved muscle endurance, increased resistance to fatigue, and prevented contraction-induced muscle injuries [10, 11, 12].
A single clinical trial and some studies in rats are insufficient to attest to the potential of apple polyphenols to improve physical performance. More clinical trials on larger populations are warranted.
4) Obesity and Blood Fat Levels
In a clinical trial on 71 moderately obese people, apple polyphenol capsules (600 mg/day for 12 weeks) reduced visceral fat, increased the levels of a hormone secreted during weight loss (adiponectin), and lowered blood cholesterol (total and LDL cholesterol) [13].
In rats fed high-fat and -sugar diets, apple polyphenols (both alone and in combination with cinnamon and birch polyphenols) reduced weight gain and insulin resistance [14, 15].
Again, a small clinical trial and some animal research cannot be considered conclusive evidence that apple polyphenols help with weight loss and high blood fat levels. Further clinical research is needed.
5) Allergic Rhinitis
In a clinical trial on 33 people with allergic rhinitis, taking apple polyphenols reduced sneezing attacks, nose discharge, and turbinate swelling, especially in those taking the highest dose [16].
This single trial is clearly insufficient to support the use of apple polyphenols in people with allergic rhinitis. More clinical research is needed to confirm its results.
6) Digestive Health
In a small trial on 12 healthy people, polyphenol-enriched apple juice increased the blood levels of over 100 different polyphenols and its metabolites. Because some of them can only be produced by certain bacterial strains, apple polyphenols may act as a prebiotic [17].
Apple polyphenols prevented stomach ulcers caused by aspirin and improved colitis in rats [18, 19].
A very small clinical trial and two studies in rats cannot be considered sufficient evidence. Larger, more robust clinical trials are needed to investigate the potential health benefits of apple polyphenols on digestive health.
7) Preventing Heart Disease
In a clinical trial on 62 overweight people, apple polyphenol extract reduced oxidative damage to the blood vessels and improved their function, helping prevent heart disease. However, another trial on 30 people with high blood cholesterol found apple polyphenols ineffective at improving blood vessel function [1, 20].
In another trial on 20 healthy people, apple polyphenols combined with vitamin C improved cardiometabolic markers (antioxidant status and blood cholesterol). However, the polyphenols alone were ineffective [4].
In mice genetically prone to high blood cholesterol, apple polyphenols helped prevent artery clogging. In another mouse strain with poor antioxidant status, apple polyphenols prevented heart rate disturbances caused by oxidative stress [21, 22].
A few clinical trials with mixed results and two studies in mice are clearly insufficient to draw any conclusions. More studies are needed to shed some light on this potential benefit of apple polyphenols.
Animal and Cell Research (Lack of Evidence)
No clinical evidence supports the use of apple polyphenols for any of the conditions listed in this section. Below is a summary of the existing animal and cell-based research, which should guide further investigational efforts. However, the studies should not be interpreted as supportive of any health benefit.
Neuroprotective Effects
Apple polyphenols protected rats from cognitive impairment caused by aluminum poisoning, possibly by chelating this metal and reducing its uptake [23].
Viral Infections
In mice infected with the common flu virus (H1N1), apple polyphenols boosted immunity and improved recovery and survival rates [24].
Limitations
There are very few clinical trials, often small, carried out so far. Although some results are promising, more studies on larger populations are needed to validate their preliminary results.
