The purpose of this study is to assess the impact of acute blueberry polyphenol intake on endothelial function of healthy volunteers. Specifically, the investigators plan to perform a randomised, double blind, cross-over human intervention trial using a blueberry drink to investigate the dose-dependent effects of blueberry polyphenols on blood vessel function using Flow mediated dilation (FMD) to measure endothelial function. The study will not only measure the acute effects of flavonoid ingestion on vascular reactivity but will also assess plasma polyphenol metabolite levels.

Inclusion Criteria:

• Male
• 18-40 years
• Healthy
• signed consent form

Exclusion Criteria:

• Blood pressure > 140/90 mmHg
• Had suffered a myocardial infarction or stroke
• Suffers from any blood-clotting disorder
• Suffers from any metabolic disorders (e.g. diabetes or any other endocrine or liver diseases)
• Any dietary restrictions or on a weight reducing diet
• Allergies or intolerances to any foods
• Smoker
• Heavy drinker (>21 units per week)
• On any lipid-modifying medication
• On any blood pressure lowering medication
• On any medication affecting blood clotting
• Taking high dose fish oil supplements (greater then 1 g EPA and DHA per day) or high doses of antioxidant vitamins (greater then 800 μg vitamin A, 60 mg vitamin C, 10 mg vitamin E or 400 μg beta carotene)
• Taking probiotics, prebiotics, synbiotics, antibiotics or anti-inflammatory or blood lowering medication within a 2-month period prior to the study
• Planning on altering consumption of vitamin supplements/fish oil capsules during the course of the study
• Undertakes strenuous exercise > 4 times per week for > 1 hour per session
• Haemoglobin levels below reference range provided by the Royal Berkshire Hospital