Benefits
Cardiovascular and Vascular Function
In a small randomized crossover study in heavy smokers, a standardized grape seed extract reduced how easily LDL cholesterol was oxidized in a laboratory test. That is a marker of oxidative stress, not a measure of heart health, and it was studied in a high risk group. None of the cited studies measured endothelial function, blood pressure, or cardiovascular events.
Antioxidant Activity
Grape seed proanthocyanidins act as antioxidants. In a small 1998 study, co authored by staff of the manufacturer, Leucoselect raised a serum antioxidant marker in volunteers. That is a blood measurement, not a demonstrated health outcome.
Microcirculation Support
None of the cited studies measured microcirculation or capillary permeability in people, so this remains a proposed effect rather than a demonstrated one.
What the LDL Oxidation Study Actually Measured
The 2003 study looked at how resistant LDL cholesterol was to oxidation in heavy smokers, not at whether cholesterol levels themselves improved. No cited trial reported changes in total cholesterol, LDL, HDL, or triglycerides.
Phytosome Delivery Format (Not a Health Benefit)
Phytosome is a format that pairs plant compounds with phospholipids, and the maker says this improves absorption. No head to head absorption study comparing Leucoselect Phytosome with standard grape seed extract is cited here, so treat that comparison as a manufacturer claim rather than a settled finding. A delivery format is also not a health benefit on its own.
Mechanism of action
OPC Antioxidant Activity
Grape seed proanthocyanidins can neutralize free radicals in laboratory testing and may help recycle vitamins C and E. This is standard antioxidant chemistry, not proof of a specific health effect in people.
Phytosome® Bioavailability Enhancement
Proanthocyanidins are poorly and variably absorbed. The phytosome format is intended to improve absorption, though no head to head absorption comparison is cited on this page.
Endothelial Nitric Oxide Support
Proposed only: grape seed compounds may support nitric oxide production in the lining of blood vessels. None of the studies cited here measured nitric oxide or endothelial function.
Capillary Integrity
Proanthocyanidins are proposed to reduce leakiness of small blood vessels. This was not measured in the human studies cited here, and this ingredient is not offered as a treatment for vein conditions.
Clinical trials
A small randomized crossover study of a standardized grape seed extract, published in Metabolism in 2003. Several authors were affiliated with the manufacturer, Indena.
Heavy smokers, chosen because smoking raises oxidative stress. Small sample.
LDL cholesterol became more resistant to oxidation in a laboratory test. That is a surrogate marker. Vascular function, blood pressure, and cholesterol levels were not shown to improve.
No pooled analysis of Leucoselect Phytosome is cited. The remaining published work is a 1998 study of a serum antioxidant marker, a 2014 descriptive observational report with no randomization and no control group, and a 2016 laboratory paper.
Small groups of healthy volunteers and frail elderly people with inflammatory and allergic conditions, plus human cells studied in a laboratory.
The 1998 study reported a change in a blood antioxidant marker. The 2014 report described immune measurements but, without a control group, cannot show cause and effect. The 2016 paper tested grape seed procyanidin extract on human lung cancer cell lines and airway cells in the laboratory; that is early bench research, not evidence that this supplement prevents or treats cancer.