Two recent studies, one published in March and the other as yet unpublished, have examined the role that fresh strawberries (Fragaria vesca) play in cardiovascular health, and the results suggest potential benefits of increased consumption.1,2 Led by Maurizio Battino, PhD, and conducted by researchers from Università Politecnica delle Marche in Ancona, Italy, and the Universities of Salamanca, Granada, and Seville in Spain, the studies used blood tests to track specific health markers in the test subjects. Both studies required participants to consume a strawberry-rich diet. The first study examined cholesterol levels in the blood, while the second evaluated red blood cells and their response to both spontaneous and induced hemolysis (the breakdown of red blood cells). The results of these studies could lead to a greater understanding of how the antioxidant phytochemicals present in the fruit interact with the human body and “[encourage] further evaluation on a population with higher cardiovascular disease risk.”1

The cholesterol study, published in the March 2014 issue of the Journal of Nutritional Biochemistry, tracked 23 healthy adult subjects as they ate approximately 500 grams (roughly 1 pound) of strawberries per day. Blood tests were taken before and after treatment to compare levels of low-density lipoproteins (LDL cholesterol), high-density lipoproteins (HDL cholesterol), and triglycerides. After 30 days, the results demonstrated a statistically significant (P < 0.05) response to treatment. LDL cholesterol levels fell by 13.7% and triglyceride levels fell by 20.8% compared to baseline.1 The levels of beneficial HDL cholesterol remained steady. Fifteen days after stopping treatment, further tests indicated that all measurements had returned to their pre-treatment values.

The second study by Battino et al. included a smaller sample size (n = 18) of different subjects and a shorter trial period of two weeks to assess the effect of the same amount of strawberries on immune response against oxidative hemolysis. Red blood cells collected from subjects were separated from plasma and suspended in a control solution to induce hemolysis.2 They observed “no significant changes” in total plasma antioxidant capacity or in serum concentrations of vitamin C or uric acid, but did note a “highly pronounced reduction in [solution]-induced hemolysis (P < 0.001)” in the red blood cells.2 The results, which will be published in the August 2014 issue of Food Chemistry, “[suggest] that a regular consumption of strawberries may enhance body defences against oxidative challenges.”2

As with all research, these studies’ findings of potential health benefits of strawberries should be interpreted prudently. The relatively small sample sizes, lack of control groups, and the amount of fresh strawberries consumed by the subjects mean that more research must be conducted before anyone claims that strawberries should be marketed or professionally recommended for those at risk of cardiovascular disease. Further, no direct evidence exists about what specifically was responsible for the observed beneficial effects in the subjects. The researchers, however, say that anthocyanins bear further scrutiny.

Anthocyanins, members of the flavonoid group of phytochemicals, are pigments that give berries their bright colors, ranging from red-orange to blue-violet.3,4 Research exploring the role of anthocyanins in health has grown during recent years, with their “free-radical scavenging and antioxidant capacities” being “the most highly publicized” aspect.3 More research is being conducted to ascertain what role they play in keeping the heart healthy, with much larger studies scrutinizing a variety of sources for anthocyanins, including strawberries. One review published in 2011 in Advances in Nutrition notes “a decreasing trend” for cardiovascular disease in the results of these studies.4

Because both of Professor Battino’s studies focused on whole-fruit consumption, there exists the question of how to translate these preliminary findings into practical applications. The study in Food Chemistry notes this particular limitation, suggesting that reduced servings may create a more reasonable continuation of the experiment.2 Similar studies have observed positive effects of heart-healthy foods such as walnuts while still using an average serving size per day, such as the study by Katz et al in Journal of the American College of Nutrition.5 In this study, subjects consumed 56 grams (about two ounces) of walnuts per day for eight weeks, with highly significant results (P = 0.019).5 Aside from portion sizes, creating a control group for a trial that uses fresh, whole fruit would present a considerable challenge, as opposed to administering the fruit in a supplement form such as a capsule, for example.

In a study to be published in the June 2014 issue of the Journal of Nutrition, researchers from Oklahoma State University, the University of Oklahoma, and Queen’s University of Belfast in Northern Ireland conducted a more controlled study by using different dosages (25 mg and 50 mg) of powdered freeze-dried strawberries in drink form.6 The placebo-controlled study examined 60 overweight adults for 12 weeks. Outcomes for this study showed a similar statistically significant (P < 0.05) trend toward the reduction of LDL cholesterol with subjects in the high-dosage group recording an average reduction of 28 mg/dL.6

Future research on the cardiovascular benefits of strawberries could use these results and limitations to move forward with well-designed human trials. Working to isolate anthocyanins and regulate the amount would remove the uncontrollable factors of the experiments, such as the variable amount of anthocyanins present in fresh, whole fruit; their interactions with other compounds of the fruit; and the effects of those compounds in humans, as the amount of dietary fiber present in strawberries also may have affected the subjects’ cholesterol levels.1 If anthocyanins are responsible for the observed outcomes, researchers could work to standardize the anthocyanin levels for a more controlled study with results that are easier to replicate.

—Hannah Bauman

1. Alvarez-suarez JM, Giampieri F, Tulipani S, et al. One-month strawberry-rich anthocyanin supplementation ameliorates cardiovascular risk, oxidative stress markers and platelet activation in humans. J Nutr Biochem. 2014;25(3):289-94. Available here. Accessed April 2, 2014.

2. Tulipani S, Armeni T, Giampieri F, et al. Strawberry intake increases blood fluid, erythrocyte and mononuclear cell defenses against oxidative challenge. Food Chem. 2014;156:87-93. Available here. Accessed April 2, 2014.

3. Lila MA. Anthocyanins and human health: an in vitro investigative approach. J Biomed Biotechnol. 2004;2004(5):306-313. Available here. Accessed April 2, 2014.

4. Wallace TC. Anthocyanins in cardiovascular disease. Adv Nutr. 2011;2(1):1-7. Available here. Accessed April 2, 2014.

5. Katz DL, Davidhi A, Ma Y, Kavak Y, Bifulco L, Njike VY. Effects of walnuts on endothelial function in overweight adults with visceral obesity: a randomized, controlled, crossover trial. J Am Coll Nutr. 2012;31(6):415-23. Available here. Accessed April 2, 2014.

6. Basu A, Betts NM, Nguyen A, Newman ED, Fu D, Lyons TJ. Freeze-dried strawberries lower serum cholesterol and lipid peroxidation in adults with abdominal adiposity and elevated serum lipids. J Nutr. 2014. Available here. Accessed April 2, 2014.