Fresh grapefruit and 100% grapefruit juice can help support a strong immune system by providing a variety of vitamins and nutrients.
- Vitamin C is commonly associated with helping maintain a healthy immune system and is abundant in grapefruit. Vitamin C strengthens our immune systems by protecting cells and promoting the production and function of immune cells. One 8-ounce glass of 100% grapefruit juice or ½ medium grapefruit are excellent sources of vitamin C, providing 60% and 50% of the Daily Value, respectively.* Daily consumption of vitamin C is important to help support your immune system during cold and flu season and all year round.
- Beneficial plant compounds, flavonoids and colorful carotenoids, work to support the immune system by fighting inflammation and helping cells communicate with each other. Improving cell communication can help strengthen our immune response when encountering infection. Grapefruit has many beneficial plant compounds which can help support a healthy immune system, with naringin being supplied in the highest amounts.
- B vitamins, such as folate, thiamin, vitamin B6, and riboflavin, may also help support the immune system through the important roles they play in enzymes needed for immune cell function, controlling oxidative stress or inflammatory response, or activating immune cells.1
Grapefruit and 100% grapefruit juice paired with a healthy lifestyle may help support a strong immune system. It’s a great source of vitamin C and contributes B vitamins and other beneficial plant compounds which may help support your family’s immune system.
Consider including nutrient-rich Florida grapefruit and grapefruit juice in your daily diet. Working to maintain a healthier immune system is also a great way to help you get through cold and flu season. Florida grapefruit and grapefruit juice may also help keep you hydrated when you’re on your way to feeling better.
Because vitamin C is a water-soluble vitamin, we need to consume it on a daily basis to help support our immune systems not only during cold and flu season, but all year long.
Detailed Nutritional Information
Vitamin C behaves as an antioxidant by scavenging Reactive Oxidative Species (ROS) and works with powerful antioxidant enzymes in the body and with vitamins (e.g. glutathione, vitamin E).2-4 Vitamin C is particularly important to the immune system as it stimulates the production and function of white blood cells and protects cells against ROS that are generated from activation of white blood cells as a result of infection and inflammatory stress.3-4
Histamine is a compound released by cells in response to allergic and inflammatory reactions. It’s involved in the presentation of symptoms such as nasal stuffiness, runny nose, teary eyes, and coughing. Vitamin C is thought to have an anti-histamine effect,5 which may help lessen cold symptom severity and support lung function.4,6
Results from some studies show that immune functions improve with increased vitamin C intake, while other studies show no effect. The inconsistency may be due to the use of adequately nourished study participants, or because leukocytes saturate with vitamin C at a lower intake than is required to saturate plasma (~100 mg/day).4
In a Cochrane review and meta-analysis combining 29 studies,7 prophylactic vitamin C supplementation reduced the incidence of colds by 52% in participants undergoing heavy physical stress (e.g., marathon runners, soldiers in subarctic conditions, skiers), while the effect was not significant in the pooled general community trials (RR 0.97 (0.94-1.00)). Vitamin C administration also reduced cold duration by 14% in children and 8% in adults, and reduced cold severity in 31 comparisons of 9,745 cold episodes. However, therapeutic trials were inconsistent in these effects.
Bioactive Plant Compounds
Research supports the role of flavonoids in the immune system. Naringin and naringenin, the most abundant flavonoids in grapefruit, have demonstrated antioxidant and anti-inflammatory properties in animal and cell models.8,9 A systematic review of randomized controlled trials testing flavonoids’ effects on the respiratory and immune system function found that among those who consumed flavonoids, there was a 33% decrease in upper respiratory tract infections in comparison to those who did not consume flavonoids.10
Carotenoids found in grapefruit and grapefruit juice, mostly beta-carotene found in pink and red varieties, can form vitamin A in the body which is important for immune function.11 Vitamin A is necessary for epithelial cell health, gene expression and immune function.12 Carotenoids have shown to have antioxidant properties and help reduce inflammation, as well as aid in the immune system.11,12 Hundreds of studies have shown carotenoids from foods (found in high amounts in fruits and vegetables) to be associated with lower risk of many diseases including macular degeneration, cardiovascular disease and many cancers including of the prostate, breast, cervix and lung.11,13
The immune system is complex and highly integrated and therefore requires the participation of virtually every macro- and micronutrient to help support innate and acquired immunity functions. B vitamins can play an important role in immunity due to their wide variety of actions in the body.14 B vitamins serve as important cofactors for various enzymes that help support the production of and pathways for immune cells. Several B vitamins, including vitamin B6, folate, and vitamin B12, play a role in intestinal immune regulation by structurally supporting the gut barrier. Vitamin B6 and folate contribute to the differentiation, proliferation and movement of certain immune cells by maintaining or enhancing natural killer cell activity. Vitamin B6 is necessary for the production of amino acids, which serve as the building blocks for cytokines, and production of antibodies and may also work in an anti-inflammatory capacity. Vitamin B6 also supports lymphocyte maturation and activity and, along with folate, is involved in T helper cell-mediated immune response. Folate is important for antibody production, metabolism, and response to antigens.
* Based on a 2000 calorie diet. FDA rounding rules applied when calculating percent DV based upon 2018 rules. Information is not intended for labeling food in packaged form. Nutrient values may vary based on brand or product types.
- Peterson et al. Nutrients. 2020;Nov 4;12(11):E3380.
- Lykkesfeldt et al. Adv Nutr 2014;5:16-18.
- Vitamin C. Linus Pauling Institute Micronutrient Information Center. Oregon State University.
- Food and Nutrition Board, Institute of Medicine. Vitamin C. Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Washington, D.C.: National Academy Press; 2000:95-185.
- Vitamin C Fact Sheet for Health Professionals. Office of Dietary Supplements. National Institutes of Health.
- Johnston et al. Subcell Biochem 1996;25:189-213.
- Hemila et al. Cochrane Database Syst Rev. 2013(1):Cd000980.
- Cavia-Saiz et al. J Sci Food Agric. 2010;90:1238–1244.
- Zeng et al. Pharmacol Res. 2018;135:122-126.
- Somerville et al. Adv Nutr. 2016;7(3):488-497.
- Carotenoids, In: Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids. Institute of Medicine. The National Academies Press, Washington, DC. 2000.
- Vitamin A, In: Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc.Institute of Medicine. The National Academies Press, Washington, DC. 2006
- Carotenoids. Linus Pauling Institute. Oregon State University.
- Gombart et al. Nutrients. 2020;12(1):236.