The complexities of the immune system make measuring the impact of dietary interventions upon its function challenging. The immune system is highly responsive to environmental influences, including the diet. An individual's diet provides the energy required to mount a strong and protective immune response, the building blocks required for synthesis of immune mediators such as antibodies and cytokines, and can also indirectly affect immune function via changes in the gut microbiome. Immune function varies across the lifecourse, with a well understood decline in immune function with age, resulting in impaired vaccination responses and an increased risk of infections and of severe complications and mortality arising from common communicable diseases such as influenza. This impaired immunity with ageing is known as immunosenescence and this affects both innate and acquired arms of the immune system.

Expert guidance is available to inform the design of human nutrition trials to ensure they include the most relevant immunological outcomes (Albers, 2013). In this study, ex vivo phagocytosis and oxidative burst of immune cells will be the primary outcome, supported by other ex vivo immune measures of high clinical relevance including functional assessment of cytokine production and expression of activation markers.

Human nutritional trials frequently omit to monitor the degree of immunosenescence in participants, even amongst studies conducted amongst older adults. For example, a recent review of pre- and probiotic trials which assessed immune responses in older adults identified that only two of thirty-six studies assessed any marker of immunosenescence (Childs & Calder, 2017).

Taxifolin/DHQ is a naturally occurring polyphenol found in apples, onions and other fruits and bark extracts. Ergothioneine is an amino acid found in mushrooms, oats and some bean varieties. We hypothesise that Taxifolin/DHQ and/or Ergothioneine will alter immune function via their established antioxidant effects, and that the effects observed will vary between older adults relative to their degree of immunosenescence.

Though current dietary guidelines advise consumption of 5 portions of fruits and vegetables per day, recent surveys reveal that fewer than 30% of adults achieve this. Antioxidants found within fruits and vegetables are understood to be one of the important aspects by which our diet can influence health. It is important to investigate the effects of such antioxidants through well designed and conducted human trials.

Inclusion Criteria:

• age 50-65yr
• BMI 18.5-30kg/m2
• Willing to avoid consumption of foods rich in Taxifolin/DHQ and Ergothioneine during the study period
• Willing to avoid taking any other food supplements or high doses of vitamins during the study period
• Able to provide written informed consent.

Exclusion Criteria:

• Use of prescription medication which may influence immune function, such as anti-inflammatory or immunosuppressant medication
• Diabetes requiring any medication
• Liver cirrhosis
• A history of drug or alcohol misuse
• Asplenia or other acquired or congenital immunodeficiencies
• Any autoimmune disease including connective tissue diseases
• Malignancy
• Laboratory confirmed SARS-CoV-2 infection within last 3 months
• self-reported symptoms of acute or recent infection (including use of antibiotics within the last 3 months)

Alphabetically labelled treatments, with de-blinding envelope held by an independent researcher at the University of Southampton.