The principal research objective is to determine whether inorganic nitrate in the form of beetroot juice compared to placebo control prevents the systemic inflammation that underlies typhoid vaccine-induced endothelial dysfunction

We wish to determine in a prospective manner whether inorganic nitrate affects the endothelial dysfunction induced by systemic inflammation. At baseline we will measure flow-mediated dilatation (FMD) and peripheral augmentation index, as well as aortic stiffness, as measured by pulse wave velocity (PWV). Volunteers will then receive ~8 mmols of dietary nitrate or nitrate free placebo juice once daily for 6 days. After this, depending on availability, volunteers will receive a typhoid vaccine Typherix®, GlaxoSmithKline UK or Typhim Vi ™, AAH Pharmaceuticals Ltd). This vaccine generates a mild systemic inflammation that is associated with vascular dysfunction. All vascular function measures will be repeated at 8 hours and 32 hours after vaccine administration.

Inclusion Criteria:

1. Healthy volunteers
2. Aged 18-45
3. Volunteers who are willing to sign the consent form.
4. Normal resting blood pressure (<140/90 mmHg)

Exclusion Criteria:

1. Healthy subjects unwilling to consent
2. Pregnant, or any possibility that a subject may be pregnant unless in the latter case a pregnancy test is performed with a negative result
3. History of any serious illnesses, including recent infections or trauma
4. Subjects taking systemic medication (other than the oral contraceptive pill)
5. Subjects with self-reported use of mouthwash or tongue scrapes
6. Subjects with recent (3 months) or current antibiotic use
7. Subjects with a history, or recent treatment of (within last 3 months) any oral condition (excluding caries), including gingivitis, periodontitis and halitosis
8. Subjects with a history of typhoid vaccination in the last 6 months
9. Subjects with any history of a blood-borne infectious disease such Hepatitis B or C virus, or HIV