The aim of the study is to investigate the relationship between dose and form of selenium on immune function, and to identify functional markers of selenium status.

One of the proposed consequences of marginal selenium status is impaired immune function. Establishing the potential role of selenium as an enhancer of immune response in vivo may provide evidence-base for public health policy, with important consequences for preventing influenza and similar diseases in the elderly.

The project consists of a placebo controlled selenium supplementation study and a dietary intervention with un-enriched and selenium enriched onions. In a parallel group design, subjects will be given either one of three doses of Selenomethionine (50, 100 or 200µg selenium/day) or a placebo per day or selenium enriched or un-enriched onions (in the form of test meals) for 12 weeks. Changes in the expression of Se-responsive genes and proteins in blood will be measured and compared with changes in plasma Se concentration and selected selenoproteins. The relationship between dietary Se intake and systemic and mucosal immune responses to influenza vaccine will be examined. Changes in immune cell populations and the influence of Se on NK and CD8 cytotoxicity will be determined by flow cytometry.

Inclusion Criteria:

• Men and women, age 50-64
• Plasma selenium level <1.2µmol/l (±10%)

Exclusion Criteria:

• Elevated blood pressure measurements (<90/50 or <95/50 if symptomatic or >160/100)
• Body mass index (BMI) <18.5 or >35
• Results of the clinical screening which are judged by the Human Nutrition Unit (HNU) Medical advisor to be indicative of a health problem and could compromise the well-being of the volunteer if they participated, or which would affect the data.
• Smokers
• Diagnosed with gastrointestinal disease (excluding hiatus hernia unless symptomatic or study intervention/procedure is contraindicated) for which they have been taking prescription drugs on a chronic basis.
• Diagnosed with a long-term illness requiring active treatment, e.g. diabetes, cancer, cardiovascular disease.
• On regularly prescribed medication known to have a profound effect on the immune function
• Regularly using antacids and laxatives (at least once a week)
• Sufferers of hay-fever taking regular steroid medication
• Unwillingness to discontinue dietary (other than vitamins and minerals) or herbal supplements less than one month prior to the start of the study and for the duration of the study
• Blood donation within 16 weeks of the first study sample and who intend to donate blood less than 16 weeks after the last study sample
• Antibiotic use within four weeks prior to starting the study
• Those who receive or plan to receive any other type of immunisation during the study period
• Those who have received an immunisation within 6 months of the start of the study
• Intention to go on holiday/trips for more than 2 weeks during the twelve week intervention
• Those planning a holiday/trip that requires immunisation during the twelve week intervention period
• Parallel participation in another research project which involves dietary intervention or sampling of biological fluids/materials
• Allergic to eggs or egg products
• Allergic to chicken protein
• Allergic to the antibiotic Gentamicin
• A history of Guillain-Barre syndrome

12 weeks