Iron is an essential micronutrient for nearly all living organisms, including microbes. The adult human body contains approximately 3-5 g of iron (45-55 mg/kg of body weight in adult women and men, respectively). Iron-deficiency related anaemia (IDA) is a major public health problem that affects more than 2 billion people globally and this represents 24.8% of the world's population. According to World Health Organisation (WHO), iron deficiency is the most common cause of anaemia worldwide, with infants, children and women at higher risk, making it a global public health problem. Much iron deficiency is a result of poor iron dietary absorption since iron is poorly absorbed (~15%). Absorption inhibition factors (iron chelators) like phytate and tannins, found in tea and vegetables have been reported to act as potent iron uptake inhibitors. Despite its health benefits, tea-containing polyphenols (tannins) have been associated with reduction and disruption of iron absorption, acting as inhibitors of non-haem iron uptake, potentially resulting in poor iron status. However, most studies on the effect of tea on iron absorption are largely based on isotope-labelled single meal studies and animal studies. Iron is a requirement of many microorganisms, as such changes in iron availability can also have an impact on the gut microbiota. Long-term controlled human intervention studies to investigate the effect of tea on iron absorption and the effect on gut microbiota composition are scarce. In addition, the impact of dietary tannins on the gut microbiota is not understood. Thus, this proposed human intervention trial will investigate the combined effect of tea-tannins on iron status, inflammation and gut microbiota composition. This will be the first study to consider this combination of factors.

Inclusion Criteria:

• Age: 18-60 years
• Gender: Male or Female
• Volunteers agree to sign an informal written consent form
• General good health
• Normal haemoglobin and serum ferritin levels

Exclusion Criteria:

• Regular tea drinkers
• Use of antibiotics, prebiotics or probiotics (in food products or as supplements), laxatives, anti-spasmodic, anti-diarrhoea drugs, (e.g. Orlistat, Lactulose) in the last 4 weeks prior to, or during the study period.
• Use of any iron supplement in the last 6 months prior to the study period.
• If participants have received bowel preparation for investigative procedures in the 4 weeks prior to the study.
• Surgical resection of any part of the bowel.
• If you have any chronic gut disorder/disease, such as IBS, IBD, etc. or other conditions that might affect the gut environment, e.g. coeliac disease. If participants are taking any medication that could affect the iron absorption (e.g. lansoprazole, omeprazole). Those with gluten allergies (e.g. Celiac disease) must be excluded as the placebo may contain gluten
• If participants are pregnant or are lactating.
• If participants have a BMI > 30 kg/m2.
• Severe allergy or any history of severe abnormal drug reaction, drug or alcohol abuse