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Review of Sweet and Tart Cherries Shows Decreased Risk of Chronic Inflammatory Diseases


Reviewed: Kelley DS, Adkins Y, Laugero KD. A review of the health benefits of cherries. Nutrients. March 2018;10(3):368. doi:10.3390/nu10030368.

Increased consumption of fruits and vegetables is associated with a decreased risk of chronic inflammatory conditions such as cardiovascular disease, stroke, diabetes, and some cancers. Fruits and vegetables provide essential vitamins and minerals, fiber, and plant compounds that have antioxidant, anti-inflammatory, and other beneficial activities. Sweet cherry (Prunus avium, Rosaceae) fruit and tart cherry (P. cerasus) fruit are rich in fiber, carotenoids, and polyphenols and contain small amounts of tryptophan, serotonin, and melatonin. Human and animal studies suggest that cherry consumption may reduce the risk of chronic diseases and improve sleep, cognitive function, and recovery from strenuous exercise. The purpose of this review was to summarize the evidence from human studies evaluating the effects of sweet and tart cherries on oxidative stress, inflammation, exercise-related muscle damage, arthritis, diabetes, cardiovascular disease, sleep, mood, and cognitive function.

MEDLINE and Google Scholar databases were searched to identify studies that used sweet cherry or tart cherry interventions. No information was provided about search terms, search strategy, or criteria for including or excluding studies in this review. No meta-analysis was conducted.

A total of 29 clinical trials were reviewed. The studies were published between 2003 and 2017, with the exception of one study published in 1950. Study treatments included tart cherries or tart cherry products (n = 20), sweet cherries or sweet cherry products (n = 7), and unspecified fresh or canned cherries (n = 2). Cherry products included juices, powders, and concentrates. Study treatments provided the equivalent of 45-270 cherries per day, corresponding to 55-720 mg of anthocyanins per day. Study populations ranged from nine to 633 participants and included healthy adults, trained athletes, elderly people with dementia, and people with arthritis, gout, obesity, diabetes, and/or hypertension. Treatment durations ranged from a single dose of cherries on one day to daily use for three months. Nineteen studies were randomized, placebo-controlled trials. The reviewed studies were grouped by medical condition or clinical markers measured, including: oxidative stress (n = 10); inflammation markers (n = 16); arthritis markers other than inflammation (n = 5); exercise-induced pain and muscle damage or recovery from exercise (n = 9); risk factors for diabetes and cardiovascular disease (n = 9); quality and quantity of sleep (n = 4); and stress, anxiety, mood, memory, and cognitive function (n = 6).

Eight of the 10 studies that measured oxidative stress found that cherries reduced oxidative stress markers or increased antioxidant capacity. Sweet cherry powder given for three days improved antioxidant capacity in healthy adults. A single dose of sweet cherries increased one antioxidant measure (oxygen radical absorbance capacity) but decreased another (ferric reducing ability of plasma [FRAP]) in healthy women. In several placebo-controlled studies, dried sweet cherries and tart cherry juice, concentrate, or fruit decreased lipid peroxidation, increased FRAP, decreased unspecified oxidative stress markers, and increased urinary antioxidant capacity in healthy adult and elderly populations. Two placebo-controlled studies found no change in oxidative stress in male athletes given tart cherry powder or juice.

Eleven of the 16 studies that measured inflammation found that cherries reduced various inflammation markers, but these reductions were significant in only nine of the 16 studies. In healthy people, single doses of sweet cherries or tart cherry juice decreased serum levels of C-reactive protein (CRP) and uric acid. In people with mildly elevated CRP levels, eating sweet cherries for 28 days decreased serum levels of CRP, interleukin-6 (IL-6), and other inflammatory markers.

No significant changes in inflammation markers were found in overweight or obese people who consumed sweet cherries for four weeks, highly trained athletes who consumed tart cherry juice or powder, elderly people with dementia who drank sweet cherry juice, or patients with osteoarthritis who drank tart cherry juice. One placebo-controlled trial found increased inflammation markers in healthy people who consumed sweet cherry powder.

Eight of the nine studies that evaluated exercise-induced pain, exercise-induced muscle damage, or recovery after exercise found that cherries reduced pain and muscle damage. However, the results of only eight studies are presented in the article. Six placebo-controlled trials with highly trained athletes found that tart cherry juice or powder improved performance, reduced post-exercise pain and muscle damage, decreased markers of muscle breakdown, and reduced recovery time. One placebo-controlled trial with male college students found that tart cherry juice reduced loss of strength, muscle damage, and pain after exercise compared to placebo. A separate study of tart cherry juice in male water polo players found no changes in performance or recovery.

All five studies that evaluated the effects of cherries on arthritis and gout found benefits. Published in 1950, the first study to test the health effects of cherries found that fresh or canned tart cherries improved joint mobility and decreased gout attacks and uric acid in the blood. Another study found that a single dose of sweet cherries decreased serum uric acid and increased urinary excretion of uric acid in healthy women. Consuming cherries or cherry extract was associated with a decreased risk of gout attacks in a case-control study. Two placebo-controlled trials found that tart cherry juice reduced serum uric acid in overweight or obese people and improved pain, stiffness, and function in people with osteoarthritis.

Five of the nine studies that evaluated the effects of cherries on risk factors for diabetes and cardiovascular disease found some health benefit from cherries. In women with diabetes, tart cherry concentrate supplementation for six weeks decreased systolic blood pressure, diastolic blood pressure, and levels of hemoglobin A1c, total cholesterol, and low-density lipoprotein cholesterol. In healthy adults, 300 mL of sweet cherry juice decreased systolic and diastolic blood pressure when taken as a single dose, but not when taken in three divided doses over three hours. In placebo-controlled trials, sweet cherry juice decreased systolic blood pressure but not diastolic blood pressure in elderly people with dementia; tart cherry concentrate lowered systolic blood pressure but not diastolic blood pressure in people with early hypertension; and tart cherry juice decreased levels of triglycerides and very-low-density lipoprotein cholesterol in overweight and obese people. The remaining studies did not show benefits from consuming cherries. It should be noted that in these few studies, cherries decreased inflammation markers associated with diabetes, metabolic syndrome, and cardiovascular disease, but did not consistently affect blood levels of lipids, glucose, or insulin.

Several studies evaluated the effects of cherries on sleep, mood, and cognitive function. In healthy adults, consuming sweet cherry powder increased total sleep time and decreased sleep latency (the time it takes to fall asleep). In placebo-controlled trials, dried sweet cherries increased total sleep time and decreased sleep latency and the number of awakenings, and tart cherry juice decreased the severity of insomnia but did not affect sleep latency or sleep efficiency in older adults with insomnia. One placebo-controlled trial found that dried sweet cherries consumed for five days improved mood and decreased anxiety in adults. A second placebo-controlled study found no effect of a single dose of tart cherry concentrate on cognitive function or mood in healthy adults. The many inconsistencies regarding the clinical studies described in the text make it difficult to summarize the overall effects of cherries on mood and cognitive function.

The authors conclude: “Evidence from published reports is reasonably strong to indicate that consumption of cherries decreased markers for oxidative stress, inflammation, exercise-induced muscle soreness and loss of strength, and blood pressure acutely after ingesting cherries.” The acute studies ranged in duration, but most of the previously mentioned effects were determined by assessments conducted within five hours of ingestion. Limited evidence suggests possible benefits in arthritis, diabetes, hyperlipidemia, sleep quality, cognitive function, and mood.

The authors explain that discrepancies among the published reports may be due to the small numbers of participants in some studies, differences in the composition of participants’ diets, short treatment periods, and variations in polyphenol content among the different types of cherries and cherry products tested. The authors recommend that stable, standardized cherry products should be developed for use in randomized controlled trials, and that future studies should have longer durations and report the anthocyanin and total polyphenol contents of the tested products.

—Sandy Jean