Headed up by Dr Philip Calder, the team identifies the citrus juices’ vitamin C, folate and polyphenol content impact immune health and inflammation as well as boost defences against bacteria and viruses.
"A weak immune system increases susceptibility to infections and allows these to become more severe,” explains Dr Calder, Professor of Nutritional Immunology at Southampton University.
One component of the immune response is inflammation. Where inflammation is excessive or uncontrolled it can damage body tissues, sometimes irreparably, and affect our ability to fight infections.
“Having a diet rich in antioxidant foods and drinks is one way to control inflammation and ensure the body can mount an effective immune response. Trials in humans confirm that orange juice consumption reduces inflammation.”
Along with Dr Elizabeth Miles, Lecturer in Nutritional Immunology at Southampton University, the review, which was funded by the European Fruit Juice Association (AIJN), looked at almost 200 studies carried out within the last 20 or so years.
These studies focus on the vitamin C and folate contained in citrus juices and their role in maintaining immunological barriers and supporting the immune function of cells including phagocytes, natural killer cells, T-cells and B-cells.
"Citrus fruit juices are particularly good sources of vitamin C and folate, which have roles in strengthening the gut and skin barriers which are our first line of defence against viruses and bacteria,” adds Dr Calder.
“In addition, these nutrients – which are absorbed well from fruit juices –support the function of many types of immune cells including phagocytes, natural killer cells, T-cells and B-cells.”
The review also discusses the different types of polyphenols contained in citrus fruit juices that include hesperidin, narirutin and naringin and their anti-inflammatory effects.
Juice & coronavirus
The paper also devotes a section to a newly emerging topic that discusses orange juice-derived polyphenols and whether they exert any anti-viral effects.
Driven by the ongoing coronavirus pandemic, the team cites evidence from in silico modelling studies that suggests hesperidin could interfere with SARS-CoV-2 entry into host cells.
Possible mechanisms action put forward include hesperidin’s ability to destabilise the interaction between the virus’ spike protein and ACE2 receptor on host cells.
Additional in vitro studies identify that hesperidin, hesperetin and naringenin can restrict viral replication acting through inhibition of key enzymes involved in this process.
Whether these effects occur in infected humans at intakes and circulating concentrations of these bioactives consistent with normal fruit juice consumption is uncertain, the review comments, adding that a clinical trial of hesperidin in people newly infected with SARS-CoV-2 has been registered.
Nutrition and Communications Consultant Dr Carrie Ruxton said of the review, “The evidence about the positive role that fruit juices play in the diet continues to build.
“We know from several large studies that a daily glass of pure fruit juice provides vitamin C, folate and potassium, can help to lower blood pressure, and reduces the risk of stroke.
“Now it's clear that citrus juices can also contribute to immune health which is crucial as we all get back to our normal lives.”
Source: Front. Immunol.
Published online: doi.org/10.3389/fimmu.2021.712608
“Effects of Citrus Fruit Juices and Their Bioactive Components on Inflammation and Immunity: A Narrative Review”
Authors: Elizabeth Miles and Philip Calder