Research - Strawberries

Strawberries - History and Traditional UseRange and Habitat

Strawberry plants are considered herbaceous perennials and have a low-growing habit, reproducing horizontally via rooting runners or stolons.1 Each plant has a compressed, modified stem from which fibrous roots grow downward and multiple stems grow upward from a rosette. Strawberry plants produce a three-part leaflet with coarsely serrated edges. Flowers are white with many stamens and often appear in clusters on short, sturdy stems arising from the crown of the plant. Each flower produces a strawberry, which, botanically speaking, is the ripened receptacle, or base, of the flower.1

Strawberries are indigenous to both Europe and the Americas.2 The modern garden strawberry (Fragaria xananassa) was developed in the 18th century from two North American species, the Virginia or scarlet strawberry (F. viriginiana), and the Chilean or beach strawberry (F. chiloensis).1 These two strains were crossed to produce larger fruit with a sweeter flavor and distinct fragrance. Today, Australia, Italy, the United States, France, Canada, New Zealand, and Japan commercially produce the largest amount of strawberries.3 The world’s leading producer of strawberries is the United States, with nearly 1.3 million metric tons produced primarily from California followed by Florida and Oregon.

Strawberries are susceptible to a wide variety of plant diseases and pests. For this reason, conventionally grown strawberry plants and fruits are often laden with pesticide and insecticide residues. The Environmental Working Group (EWG) considers the strawberry one of its “Dirty Dozen,” a list of 12 commonly consumed, conventionally grown produce items that are consistently high in harmful pesticide residues.4

Phytochemicals and Constituents

Strawberries, like most dark-colored berries, contain a complex series of phytochemicals that can be divided into six main groups: anthocyanins, flavonols, flavanols, ellagitannins, ellagic acid glycosides, and cinnamic acid conjugates.5 These compounds have significant health benefits and have been studied for their anti-cancer, antimicrobial, antioxidant, anti-parasitic, and antiviral activities, as well as their ability to regulate blood glucose.

Anthocyanins are well-known for their antioxidant properties, as well as giving the berries their red color6; flavonols such as quercetin have antihistamine and anti-inflammatory properties and are considered important in cancer prevention.7 Strawberries also contain a significant amount of proanthocyanidins, a flavanol compound that recently has gained more attention and scientific study. Though grapes (Vitis vinifera), cranberries (Vaccinium macrocarpon), and cacao (Theobroma cacao) are the most well-known common food sources of proanthocyanidins, strawberries contain higher concentrations than both red and green grapes.8 Proanthocyanidins and foods with high levels of the compounds also are being investigated at the in vitro level for their anti-fungal properties, specifically against oral Candida strains.9-11

Historical Uses

The Romans were the first to record medicinal uses of the strawberry, and the practice spread to Greece. The berries were believed to be a cure for gout and helpful for digestive problems.12 During the 16th and 17th centuries, strawberries were cultivated and considered to be part of a healthy diet. Thomas Culpeper, medieval herbalist, noted that strawberries were “singularly good for the healing of many ills,” and while the leaves were the primary plant part used in medicinal preparations, Carl Linnaeus recorded and reportedly proved the efficacy of the berries as a treatment for rheumatic gout.13 The leaves are mildly diuretic and astringent due to their high tannin content, and have been used as a laxative.14

The leaves, fruit, crowns, and roots were used in the preparations of ointments, medicinal teas, and syrups.12 The pulp and juice of the berry were also used in cosmetic preparations, including treatments for teeth whitening, skin whitening, and healing sunburns.13 Today the plant is rarely used medicinally; however, a tea prepared from the leaves is used to treat diarrhea and dysentery. Currently, strawberries enjoy widespread popularity and use as a food. The berries are used in baked goods, desserts, ice cream, pies, gelatin desserts, soft drinks, jellies, syrups, and in the production of wines and liquors.15

Modern Research

The consumption of fruits and vegetables abundant in bioactive compounds and antioxidants — including topical skin application of polyphenols from a variety of dietary sources — has been shown to have a role in the prevention of numerous diseases including skin pathologies, different types of cancer, cardiovascular disorders, as well as age-related degenerative conditions.16 Recent animal studies have shown a potential role of strawberry consumption in improving the aging process, reducing oxidative damage, and improving antioxidant defense.17,18

Other recent in vivo studies have shown positive dietary polyphenol effects including prevention of gastric cancer progression, reduction of inflammation, improvement of plasma lipid profile, reduction of myocardial infarction risk, and increased plasma antioxidant capacity.19,20 Human studies examining polyphenol supplementation have shown that the consumption of 300 g of fresh strawberries significantly enhanced the total antioxidant capacity and serum vitamin C concentration in young, healthy patients.21One human study showed that an elevated anthocyanin intake, such as the anthocyanins present in strawberries, reduced the risk of myocardial infarction in young and middle-aged women.22 Another human study with young, healthy volunteers consuming 500 g of strawberries daily for one month showed a reduction in triglyceride levels, LDL cholesterol, and total cholesterol.23 The berry’s anthocyanin and dietary fiber content were thought to contribute to this result. However, the average serving size of strawberries is approximately 100 g, making the whole-fruit approach of the previous studies difficult to control and impractical to implement. A similar, placebo-controlled study examined the effect of freeze-dried strawberry powder in drink form on overweight adults and showed a similar trend toward the reduction of LDL cholesterol.24

AbstractStrawberries are an important fruit in the Mediterranean diet because of
their high content of essential nutrients and beneficial
phytochemicals, which seem to exert beneficial effects in human health.
Healthy volunteers were supplemented daily with 500 g of strawberries
for 1 month. Plasma lipid profile, circulating and cellular markers of
antioxidant status, oxidative stress and platelet function were
evaluated at baseline, after 30 days of strawberry consumption and 15
days after the end of the study. A high concentration of vitamin C and
anthocyanins was found in the fruits. Strawberry consumption
beneficially influenced the lipid profile by significantly reducing
total cholesterol, low-density lipoprotein cholesterol and triglycerides
levels (−8.78%, −13.72% and −20.80%, respectively; P<.05)
compared with baseline period, while high-density lipoprotein
cholesterol remained unchanged. Strawberry supplementation also
significant decreased serum malondialdehyde, urinary 8-OHdG and
isoprostanes levels (−31.40%, −29.67%, −27.90%, respectively; P<.05).
All the parameters returned to baseline values after the washout
period. A significant increase in plasma total antioxidant capacity
measured by both ferric reducing ability of plasma and oxygen radical
absorbance capacity assays and vitamin C levels (+24.97%, +41.18%,
+41.36%, respectively; P<.05) was observed after strawberry
consumption. Moreover, the spontaneous and oxidative hemolysis were
significant reduced (−31.7% and −39.03%, respectively; P<.05),
compared to the baseline point, which remained stable after the washout
period. Finally, strawberry intake significant decrease (P<.05)
the number of activated platelets, compared to both baseline and
washout values. Strawberries consumption improves plasma lipids profile,
biomarkers of antioxidant status, antihemolytic defenses and platelet
function in healthy subjects, encouraging further evaluation on a
population with higher cardiovascular disease risk.Source : The Journal of Nutritional BiochemistryLink to Abstract

Berries Ward Off MI in Women

Young and middle-age women whose diet included high levels of anthocyanins -- the flavonoids present in red and blue fruits such as strawberries and blueberries -- had a significantly reduced risk for myocardial infarction (MI), a large prospective study found.

Women whose anthocyanin intake was in the highest quintile had a 32% decrease in risk of MI during 18 years of follow-up (HR 0.68, 95% CI 0.49 to 0.96, P=0.03), according to Eric B. Rimm, ScD, of Harvard University, and colleagues.

And in a food-based analysis, women who consumed more than three servings of strawberries or blueberries each week showed a trend towards a lower MI risk, with a 34% decrease (HR 0.66, 95% CI 0.40 to 1.08, P=0.09) compared with women who rarely included these fruits in their diet, the researchers reported online in Circulation.

"Growing evidence supports the beneficial effects of dietary flavonoids on endothelial function and blood pressure, suggesting that flavonoids might be more likely than other dietary factors to lower the risk of [coronary heart disease] in predominantly young women," they observed.

A number of preclinical experiments have demonstrated cardioprotective effects of anthocyanins, including anti-inflammatory effects, plaque stabilization, and inhibition of the expression of growth factors.

While studies have suggested that MI risk is increased in young and middle-age women who smoke or use oral contraceptives, little is known about the influence of diet in this population, whose risk may differ from that in older women.

The younger women may have a greater likelihood of endothelial dysfunction and coronary vasospasm and less obstructive disease.

Because dietary flavonoids -- found in vegetables, fruits, wine, and tea -- are recognized as benefiting endothelial function, the researchers looked at outcomes for 93,600 women enrolled in the Nurses' Health Study II who reported their consumption of various foods and their lifestyle factors every 4 years.

At the time of enrollment, beginning in 1991, participants were ages 25 to 42.

During almost 2 decades of follow-up, there were 405 cases of MI, occurring at a median age of 48.9 years.

Review of the food frequency and lifestyle questionnaires revealed that women who consumed high levels of anthocyanins were less likely to smoke, were more physically active, and had lower fat and higher fiber intake.

The 32% reduction in MI risk was seen after adjustment for multiple factors including body mass index, physical activity, saturated fat intake, use of caffeine and alcohol, and family history of MI.

"This inverse association was independent of established dietary and nondietary [cardiovascular disease] risk," the researchers noted.

Even adding conditions such as hypertension, dyslipidemia, and diabetes to the analytical model did not significantly change the risk estimate (HR 0.70, 95% CI 0.50 to 0.97).

Comparison of risk among women in the highest and lowest 10% of anthocyanin intake showed a relative risk of 0.53 (95% CI 0.33 to 0.86) for the high-intake group, which suggested the presence of a dose-response relationship.

Intake of other types of flavonoids did not significantly lower the risk of MI. The researchers had hypothesized that high intake of flavan-3-ol also would be important, because they had previously identified cardiovascular benefits for one type of flavan-3-ol compound in a meta-analysis.

The lack of effect in the current analysis may have reflected the fact that in the early 1990s, when the study began, most food frequency questionnaires did not include dark chocolate, which is a primary source for flavan-3-ol, they noted.

Adjustment for additional dietary factors such as total fruit and vegetable consumption also did not alter the risk, which suggests "that the benefits are specific to a food constituent in anthocyanin-rich foods (including blueberries, strawberries, eggplants, blackberries, blackcurrants) and not necessarily to nonspecific benefits among participants who consume high intakes of fruits and vegetables."

However, the results of this study do not support the use of flavonoid dietary supplements, according to Michael Rinaldi, MD, of the Carolinas HealthCare System's Sanger Heart and Vascular Institute in Charlotte, N.C.

The study does suggest that a healthy diet that includes fruits and vegetables can be healthy, said Rinaldi, who was not involved in the study.

"On the other hand, if you're going to say that these flavonoid substances in the berries should be taken as supplements, that's not what the study has the power to say," he told MedPage Today in an interview.

Limitations of the study included a lack of information about the results of cardiac catheterization and the possibility of additional unmeasured confounding factors.

In addition, while the model adjusted for intake of a number of other potentially beneficial food components, there may have been other unidentified compounds in fruits that contribute to cardioprotection.

"In a population-based study like ours, it is impossible to disentangle the relative influence of all the constituents of fruits and vegetables," the researchers wrote.

Further research will be needed to identify cardiac biomarkers that could help explain mechanisms of action, to explore dose responses, and to evaluate longer-term clinical endpoints.

An experiment has shown that strawberry extract added to skin cell cultures acts as a protector against ultraviolet radiation as well as increasing its viability and reducing damage to DNA. Developed by a team of Italian and Spanish researchers, the study opens the door to the creation of photoprotective cream made from strawberries.

"We have verified the protecting effect of strawberry extract against damage to skins cells caused by UVA rays," as explained by Maurizio Battino, researcher at the Università Politecnica delle Marche in Italy and lead author of the jointly Spanish and Italian study. The results are published in the 'Journal of Agricultural Food Chemistry'. The team prepared human skin cell cultures (fibroblasts) and added strawberry extract in different concentrations (0.05, 0.25 and 0.5 mg/ml), the only exception being the control extract. Using ultraviolet light, the samples were then exposed to a dose "equivalent to 90 minutes of midday summer sun in the French Riviera." Data confirm that the strawberry extract, especially at a concentration of 0.5 mg/ml, displays photoprotective properties in those fibroblasts exposed to UVA radiation, it increases cell survival and viability and decreases damage in the DNA when compared with control cells. "These aspects are of great importance as they provide protection for cell lines subject to conditions that can provoke cancer and other skin-related inflammatory and degenerative illnesses," outlines Battino. The researcher recognises that this is the "first step in determining the beneficial effects of strawberries in our diet or as a possible compound source for 'food integrators' or cosmetics for instance." The redness of anthocyanins But what molecules give strawberries their photoprotective properties? Scientists suspect that it could be the anthocyanins, which are pigments that give leaves, flowers and fruits their red colour. Analyses have confirmed that extracts are rich in such substances. "These compounds have important anti-inflammatory, antioxidant and anti-tumour properties and are capable of modulating enzymatic processes," explains another of the authors, Sara Tulipani from the University of Barcelona. She adds that "we have not yet found a direct relationship between their presence and photoprotective properties." "At the moment the results act as the basis for future studies evaluating the 'bioavailability' and 'bioactivity' of anthocyanins in the dermis and epidermis layers of the human skin, whether by adding them to formulations for external use or by ingesting the fruit itself," states Tulipani. Also made up of researchers from the Universities of Salamanca and Granada, in its previous works the team had already demonstrated that strawberries (Fragaria x ananassa) strengthen the red bloods cells and protect the stomach from the effects of alcohol.