The purpose of this study is to establish an effect of monomeric and oligomeric flavanols supplementation on exercise blood pressure and vascular function in healthy volunteers.

Exaggerated exercise blood pressure (BP) response in healthy subjects is recognized as a risk factor of hypertension and cardiovascular events. Pathogenetically exaggerated BP response is attributed to compromised vascular(endothelial) functions as well as oxidative stress and inflammation. Monomeric and oligomeric flavanols (MOF) are dietary components with well-characterized beneficial effects on the redox homeostasis, endothelial function and microvascular health.

The objectives of the study will be to evaluate the effects of MOF in comparison to placebo on exercise blood pressure, endothelial function, inflammatory and redox status in healthy prehypertensive volunteers. In addition, the study will aim to assess the impact of MOF supplementation on the exercise-induced renin-angiotensin-aldosterone system (RAAS) activation and extracellular matrix remodelling.

After being informed about the study and potential risks all volunteers signing informed consent form will undergo screening to determine eligibility for the study. Eligible subjects will be randomized in the double-blind manner to monomeric and oligomeric flavanols /placebo or placebo/monomeric and oligomeric flavanols sequence (cross-over design) in a 1:1 ratio. Monomeric and oligomeric flavanols are derived from grape seeds extract and will be administered in a dose 200 mg per day.

Inclusion Criteria:

1. Healthy men and women with normal to high-normal resting BP (SBP 120 - 139 mm Hg and DBP 80 - 89 mm Hg).
2. Age 35 - 65 years
3. BMI 20 - 32 kg/m^2
4. Hypertensive response to maximal exercise test defined as SBP ≥ 200 mm Hg (men) and ≥ 180 mm Hg (women).

Exclusion Criteria:

1. Active engagement in the weight loss programs, also including slimming diets.
2. Active smoking or abstinence from smoking for less than one year.
3. Use of medications that reduce BP and/or can potentially influence other study outcomes (ACE-inhibitors, angiotensin receptor blockers, diuretics, painkillers, etc).
4. Intake of polyphenol-containing supplements for two month before and during the whole course of the study.
5. History of diabetes, cardiovascular, respiratory, renal, gastrointestinal, hepatic or other diseases and conditions, which potentially can compromise participation in this study.
6. Intense sporting (>10 h/week) and/or participation in the competition at the professional level.
7. Pregnancy or breastfeeding.
8. Participation in a clinical trial within 4 weeks prior to inclusion into this study.
9. Vaccination against Covid-19 within two months before the screening/randomization visit or expected vaccination against Covid-19 during the study