The Effect of Tea on Vascular Function and Insulin Sensitivity

Can Tea Prevent Impairments in Vascular Function and Insulin Sensitivity Induced by 7-days Physical Inactivity and Overfeeding in Healthy Men

The aim of this research is to explore changes in peripheral/cerebrovascular function and insulin sensitivity after a 7-day combination of physical activity reduction (-50% steps per day) and overfeeding (+50% kcal per day, comprising 65% fat) in healthy male volunteers, and examine whether daily intake of tea can prevent such changes.

The aim of this study is to explore the impact of a 7-day 'unhealthy' lifestyle that combines physical activity reduction (-50% steps per day) and overfeeding (+50% kcal per day, comprising 65% fat) on peripheral (conduit artery and skin microvessels) and cerebrovascular function and insulin sensitivity in healthy male participants. Moreover, the investigators will explore whether the detrimental impact of this lifestyle can be mitigated by daily tea consumption (equivalent to 6 cups/day). To explore this hypothesis, the investigators will perform measurements of these parameters before and after 7-days of reduced physical activity and overfeeding, with and without the combination of daily tea ingestion.

tea, cardiovascular, vascular, metabolism, microcirculation, physical inactivity, polyphenols, conduit artery, endothelial function, cerebrovascular, insulin sensitivity

The intervention product is regular green tea brewed with hot water in a large quantity. The tea obtained is dried and the powder, with added sugar, is distributed over sealed aluminium sachets (1 gram of powder per sachet). The product has been cleared for consumption by Unilever's Microbiology Department and the independent Safety and Environmental Assurance Centre of Unilever.

A product of similar colour and taste, but not the presumed actives of tea (polyphenols), is used as placebo. The product has been cleared for consumption by Unilever's Microbiology Department and the independent Safety and Environmental Assurance Centre of Unilever.

This will be measured following a carbohydrate-rich meal tolerance test (MTT) after an overnight fast, combined with regular venous blood sampling of insulin and glucose.

Peripheral vascular function will be measured via endothelial-dependent flow-mediated dilation (FMD) of the brachial and femoral arteries, with microcirculatory function being assessed using local thermal hyperaemia and laser Doppler flowmetry (LDF), in addition to full-field laser perfusion imaging (FLPI). Cerebrovascular function will be examined via transcranial Doppler.

Inclusion Criteria: Aged 18-55 years Male Habitually active (>8,000 steps/day) Healthy Exclusion Criteria: Smokers Medical history of cardiovascular/metabolic disease Family history of cardiovascular disease (first degree relatives) On medication known to influence the cardiovascular system BMI of <18 or >30 kg/m2 Known food allergies or special dietary requirements Vaccination (<1 week) due to induced systemic inflammatory reaction