Latest Nutrition Research

California Strawberries: Guardians of Health

The Dietary Guidelines for Americans, 2015 recommend consuming more fruits and vegetables for three key reasons:
  • • Fruits and vegetables are major contributors of a number of nutrients that are under-consumed in the U.S. diet, including vitamin C, folate, potassium and dietary fiber.
  • • Eating fruits and vegetables is associated with reduced risk of many chronic diseases, including cardiovascular disease, and may be protective against certain types of cancers.
  • • Foods relatively low in calories, such as fruits and vegetables, can help manage weight when eaten in place of higher calorie foods.
In addition to the contribution that strawberries make to nutrients that are in short supply in our diets, nutrition scientists are working to characterize and understand the health-promoting actions of the hundreds of bioactive compounds in plant foods, as well as the protective power of the foods themselves. The potential impact of strawberries in human health has been studied in a variety of conditions, including cardiovascular health, cancer prevention, cognitive function and inflammation. Strawberries continue to be at the forefront of nutrition research in the 21st century.

Strawberries and Cardiovascular Health

Strawberries contain a number of cardio-protective nutrients and plant compounds, including vitamin C, folate, and potassium; flavonoids such as anthocyanin, ellagic acid, quercetin and kaempferol; and dietary fiber. Research indicates that consumption of strawberries not only increases blood levels of these nutrients and phytochemicals but also lowers markers of cardiovascular disease, including total and LDL cholesterol, homocysteine levels and blood pressure.
Researchers evaluated the effectiveness of strawberries in lowering cardiovascular risk factors in individuals with metabolic syndrome by supplementing the diets of 27 subjects with 50g of freeze-dried strawberries (the equivalent of three cups of fresh strawberries) daily for eight weeks. Strawberry supplementation was shown to significantly decrease total and low-density lipoprotein cholesterol and positively impact other markers of atherosclerosis, including lipid particle size and circulating levels of vascular cell adhesion molecules. (Basu A, et al. Nutr Res. 2010;30:462-469.) These findings support results of a previously published study of short-term supplementation of freeze-dried strawberries in women with metabolic syndrome which showed that strawberry consumption exerted cholesterol-lowering effects and decreased lipid peroxidation. (Basu A, et al. Nutr J. 2009;8:43.)
In a study designed to assess the effects of adding strawberries as a source of antioxidants to improve the overall antioxidant effect of a cholesterol-lowering diet (dietary portfolio), researchers noted that when strawberries were added to the diet in an amount of one pound per 2,000 calories (about three cups per day), the palatability of the diet was improved without reducing its effectiveness in lowering blood lipids or blood pressure. Additionally, the researchers found that strawberry supplementation was effective in reducing oxidation of circulating LDL, suggesting a role in helping to lower coronary heart disease risk (Jenkins DJ, et al. Metabolism Clinical and Experimental. 2008;57:1636-1644.)
Results of a study of the dietary intake records of approximately 27,000 women who participated in the decade-long Women’s Health Study showed that women who had a higher intake of strawberries (two or more servings per week) were more likely to follow a heart-healthy diet. On average, women in the highest strawberry intake group ate about twice as many servings of fruits and vegetables every day as did women in the lowest intake group. Also, those with the higher intake of strawberries were less likely to have elevated levels of C-reactive protein- a biomarker of inflammation- than women who reported eating none in the previous month. (Sesso HD, et al. J Am Coll Nutr. 2007;26-303-310.)

Strawberries and Cancer Prevention

In addition to vitamin C and folate, phytochemicals with potent antioxidant properties such as the polyphenols found in strawberries are believed to play a role in the prevention and treatment of a variety of chronic diseases, including cancer. Dietary antioxidants are thought to exert their effects by offering protection against inflammation and oxidative stress that can cause DNA damage, scavenging free radicals and protecting cell membranes from lipid peroxidation.
Strawberries are a good source of folate, a B vitamin that has been associated with reduced risk of several cancers, including colorectal cancer. Epidemiological studies also suggest that folate may be protective against cervical dysplasia, an early precancerous stage that sometimes proceeds to cervical cancer.
A number of in vitro and in vivo animal studies have demonstrated the anti-cancer properties of berry extracts and berry phenolics. For example, quercetin, a flavonoid found in strawberries, has been shown in animal studies to inhibit chemically-induced cancers of the lung, tongue, colon, mammary glands and mouth. Quercetin also has been found to inhibit the growth of human prostate cancer cells and human breast cancer cells.
The phytochemical ellagic acid has shown promise in inhibiting cancer formation and progression in laboratory animals and cell cultures, including human cell lines. Several animal studies have shown that ellagic acid can inhibit the growth of tumors of the lung, esophagus, and skin, as well as other chemically-induced caners. One serving of strawberries (one cup) contains approximately 63 mcg of ellagic acid.
Results from preliminary studies using freeze-dried strawberries and strawberry extracts in cell and animal models have been promising in preventing changes in cells that could progress toward cancer. A cell culture study using two varieties of freeze-dried strawberries added to two types of breast cancer cells and two types of cervical cancer cells showed both strawberry varieties significantly inhibited the growth of both types of cervical cancer cells. Both varieties also inhibited both types of breast cancer cells, although one variety was more potent than the other.
In a study conducted in provinces in China where the population is at the highest risk for esophageal cancers in the world, researchers assessed the effect of receiving two doses of freeze-dried strawberries (30g and 60g) daily for six months. The doses were applied to a group of 75 patients with premalignant esophageal lesions. Results showed that growth of the lesions slowed significantly in 29 of the 36 participants who received the 60g dose, and that this treatment also significantly inhibited protein expression and cell proliferation. The researchers suggest that the strawberries played a role in down-regulating inflammation, oxidative stress and cell proliferation associated with cancer promotion/progression. (Chen T et al. Cancer Pev Res. 2012;5:41-50.)

Strawberries and Cognitive Function

Age-related declines in cognitive function have been related to both oxidative stress and inflammation. The decline is manifested as alterations in both motor function and cognitive behaviors. Alterations in motor function may include decreases in balance, muscle strength and coordination, while cognitive deficits include losses in learning ability and memory. Because of their high antioxidant and anti-inflammatory activities, strawberries are being studied for their ability to slow or prevent such decline.
A review article by researchers at the USDA Human Nutrition Research Center on Aging at Tufts University identified phenolic compounds, particularly anthocyanins, found in strawberries and other berry fruits, to have potent antioxidant capacities and anti-inflammatory properties. These compounds can have direct effects on the brain and help modulate behavior during aging. Preclinical research in animal models has demonstrated the effects of these phytochemicals on enhanced cognition and motor control. (Miller MG, et al. J Agric Food Chem. 2012; 60:5709-5715.)
An observational study of the association between the long-term dietary intakes of flavonoids, including anthocyanidins, and cognitive decline was conducted in a sample of 16,010 women, aged >70 years, enrolled in the Nurses’ Health Study. Researchers found greater intakes of strawberries (>two servings per week) were associated with slower rates of cognitive decline, appearing to delay cognitive aging by up to 2.5 years. The researchers concluded that a simple dietary recommendation such as increasing berry consumption may have meaningful public health implications for older adults. (Devore EE, et al. Ann Neurol. 2012;72:135-143.)

Strawberries and the Inflammatory Process

A growing body of research is revealing how chronic inflammation and obesity are related to the development of a number of diseases, including heart disease, stroke, type 2 diabetes and cancer. Studies continue to show a positive association between consumption and cardiovascular health as well as the fruit’s role in mediating inflammation.
A seven-week, double-blind, randomized, cross-over pilot study was conducted to determine the effect of strawberries on inflammatory mediators and blood lipid profiles in obese individuals. Twenty healthy obese adults were fed a prepared diet of three meals a day that typified the average American diet, one with a strawberry-flavored control intervention and one with the equivalent of four servings of frozen strawberries daily (as freeze-dried strawberry powder). After the three-week strawberry powder intervention, subjects exhibited reduced blood cholesterol levels and positive alterations in lipid subfractions. These observations suggest a role for strawberries as a dietary strategy to reduce obesity-related disease risk. (Zunino SJ et al. Br J Nutr. 2012;108:900-909.)
In a study designed to measure the protective effects of strawberry consumption on biomarkers of oxidative and inflammatory stress induced by a high carbohydrate/high fat meal, 24 overweight adults were randomized to receive a daily strawberry beverage containing the equivalent of about 2/3 cup of fresh strawberries or a placebo for six weeks. Results showed that strawberry consumption positively influenced meal-induced stress response signals associated with inflammation and fibrinolytic activity, suggesting a role for strawberries in reducing disease risk and maintaining cardiovascular health. (Ellis CL, et al. J Atheroscler Thromb. 2011;18:318-327.)
Another study looked at the postprandial metabolic effects of consuming a strawberry-containing beverage along with a high carbohydrate moderate fat meal in overweight individuals. The results showed inflammatory responses were significantly diminished as measured by high-sensitivity C-reactive protein and Interleukin 6, and that insulin sensitivity was reduced. The researchers concluded that the polyphenolic-rich content of strawberries, in addition to their glutathione and high vitamin C content played a role in mediating the inflammatory response and reducing insulin resistance. (Edirisinghe I, et al. Br J Nutr. 2011;106:913-922.)