Can strawberries support your immune system? Evidence from clinical studies suggest they can.
In light of Covid-19, also known as the coronavirus, misleading claims are being made regarding products that can keep the immune system not only healthy, but also prevent people from contracting the virus.
Recognizing that strawberries are the one fruit being purchased more due to their protective packaging and vitamin C, I wanted to clarify briefly what affects the immune system, and whether strawberries play a role.
Factors that can influence immunity include non-genetic behaviors and bacteria[i]:
How Does Diet Factor into Immunity?
Whole foods can promote overall health. While there is no single food that will boost your immune system to the point of preventing any disease, eating a balanced diet will help maintain a strong immune system.
The Dietary Guidelines for Americans promotes the “My Plate” method of balancing your diet:
Colorful fruits and non-starchy vegetables make up ½ your plate
Lean protein makes up ¼ of your plate
Whole grains or starch make up the last ¼ of your plate
Low-fat dairy is optional at each meal for those who tolerate lactose[ii].
Will Strawberries Boost My Immune System?
Because of strawberries’ high vitamin C content and their protective plastic packaging, individuals have been buying extra clamshells of strawberries. Healthcare professionals support this even though no foods can actually "boost" immunity.
Some question if vitamin C supplements aren’t proven to enhance immunity, why would health professionals support eating more strawberries?
To begin with, vitamin C from fruit and veggies is the best source of vitamin C- not supplements.[iii] Food sources of vitamin C are more effective at supporting the immune system and overall health than supplements.
In addition, strawberries offer much more than vitamin C; all of their micronutrients work together synergistically to help prevent and fight disease.
Based on clinical evidence, here are the facts about strawberries’ immune-building properties:
Young and older people with underlying chronic conditions including heart disease, high blood pressure, cancer, respiratory dysfunction, and diabetes are at higher risk for contracting COVID-19.[iv] Strawberries have been shown to fight against many chronic diseases by helping to lower LDL cholesterol [v],[vi], carcinogenic activity[vii], blood sugars and insulin resistance [viii],[v] and improving artery function.[ix]
Strawberries may increase the immunological response of the immunity cells T-lymphocytes and monocytes in obese people who are at greater risk for developing infections.[x]
The red berries help support cell survival, growth, and antioxidant defense. [iii]
Strawberries protect and repair DNA damage. [iii]
A serving of strawberries has a full day’s worth of vitamin C. [xii]
Strawberries display antimicrobial action. [v]
Strawberries act as a probiotic and can positively alter the gut microbiome when eaten daily. [v]
In a study of healthy adults, eating strawberries for short- and medium-term led to significant increases in antioxidants, folate, and vitamin C in the body as well as to significant improvements of white blood cell resistance to external stress.[xiii]
Do Supplements Help the Immune System?
Outside of supplementing with vitamin D if you’re deficient in the vitamin (many are in the winter who live in northern climates), there is no clinical evidence that supplements are effective in bolstering the immune system, despite the many dubious claims being made on social media, TV ads, and the internet.
There is little evidence that popping extra zinc lozenges, vitamin C tablets, elderberry or echinacea can help. In fact, you can do damage by overloading on certain vitamins (like vitamin C and zinc), minerals, and any supplements not prescribed by a doctor [ii].
What Can I Do to Build My Immunity?
The best actions you can take to build your immune system up refers back to the list of behaviors at the top of this article.
Eat a well-balanced diet with the rainbow of fruits and vegetables each week to increase your antioxidant, vitamin, and mineral stores. Eight strawberries are equivalent to 1 serving of fruit, and a full day’s worth of vitamin C.
Protein is also essential for growth and illness recovery. If you choose vegetarian protein, eating vitamin C-rich foods with plant protein increases absorption of iron that is otherwise low in bioavailability.
Do your best to get adequate sleep each night (7-8 hours each night).
While anxiety and stress are expected right now, techniques to help manage it may include talking to someone, checking in on loved ones, exercise, sleep, and eating a nutritious diet.
Microbiome & Germs
We can’t neglect the role our bacteria play in all of this. While we may be wiping out harmful germs and bacteria on surfaces, it’s critical to feed our guts good bacteria via pre- and pro-biotic foods like yogurt, fruits, vegetables, and fermented foods.
Heed advice of health authorities. The CDC website is a reliable source of information on the coronavirus and other infectious diseases.
Virtual nutrition appointments are available with a Registered Dietitian here.
[i] Brodin, P., Jojic, V., Gao, T., Bhattacharya, S., Angel, C. J., Furman, D., Shen-Orr, S., Dekker, C. L., Swan, G. E., Butte, A. J., Maecker, H. T., & Davis, M. M. (2015). Variation in the human immune system is largely driven by non-heritable influences. Cell, 160(1-2), 37–47. https://doi.org/10.1016/j.cell.2014.12.020 [ii]United States Department of Agriculture. (2020). What is my plate? ChooseMyPlate.gov. https://www.choosemyplate.gov/eathealthy/WhatIsMyPlate [iii]Office of Dietary Supplements. (2020). Vitamin C. National Institutes of Health. https://ods.od.nih.gov/factsheets/VitaminC-Consumer/ [iv]Rabin, R.C. (March 12, 2020). Coronavirus is an even worse threat to more than half of Americans. New York Times. https://www.nytimes.com/2020/03/12/health/coronavirus-midlife-conditions.html [v]Djurica, D., Holt, R., Ren, J., Shindel, A., Hackman, R., & Keen, C. (2016). Effects of a dietary strawberry powder on parameters of vascular health in adolescent males. British Journal of Nutrition, 116(4), 639-647. doi:10.1017/S0007114516002348 [vi]Burton-Freeman, B., Linares, A., Hyson, D., & Kappagoda T. (2010). Strawberry modulates LDL oxidation and postprandial lipemia in response to high-fat meal in overweight hyperlipidemic men and women. Journal of the American College of Nutrition, 29(1):46-54. 10.1080/07315724.2010.10719816 [vii]Zhang Y, Seeram NP, Lee R, Feng L, Heber D. (2008). Isolation and identification of strawberry phenolics with antioxidant and human cancer cell antiproliferative properties. Journal of Agriculture & Food Chemistry, 56(3), 670-675. [viii] Eunyoung, P., Edirisinghe, I., Wei, H., Prabha, L., Katarzyna, V., et al. (2016). A dose–response evaluation of freeze‐dried strawberries independent of fiber content on metabolic indices in abdominally obese individuals with insulin resistance in a randomized, single‐blinded, diet‐controlled crossover trial. Molecular Nutrition & Food Research, 60(5), 1099-1109. https://doi.org/10.1002/mnfr.201500845 [ix]Tulio, Jr. A.Z., Chang, C., Edirisinghe, I., White, K.D., Jablonski JE, et al. (2012). Berry fruits modulated endothelial cell migration and angiogenesis via phosphoinositide-3 kinase/protein kinase B pathway in vitro in endothelial cells. Journal of Agriculture & Food Chemistry, 60(23), 5803-12. doi: 10.1021/jf3001636. [x]Zunino, S., Storms, D., Freytag, T., Mackey, B., Zhao, L., Gouffon, J., & Hwang, D. (2013). Dietary strawberries increase the proliferative response of CD3/CD28-activated CD8 T cells and the production of TNF-α in lipopolysaccharide-stimulated monocytes from obese human subjects. British Journal of Nutrition, 110(11), 2011-2019. doi:10.1017/S0007114513000937 [xi]Giampieri, F., Forbes-Hernandez, T.Y., Gasparrini, M., Alvarez-Suarez, J.M., Afrin, S., et al. (2015). Strawberry as a health promoter: An evidence based review. Food & Function, 6, 1386-1398. https://doi.org/10.1039/C5FO00147A [xii]USDA. (2020). National Nutrient Database for Standard Reference (version 1.2.2, release 25) [computer software]. [xiii]Battino, M., Forbes-Hernandez, T.Y., Gasparrini, M., Afrin, S., Mezzetti, B. and Giampieri, F. (2017). The effects of strawberry bioactive compounds on human health. Acta Hortic. 1156, 355-362. https://doi.org/10.17660/ActaHortic.2017.1156.54