Absorption of Resveratrol

A large proportion of the research conducted on resveratrol has used cell culture that is exposed to unmetabolized resveratrol. When consumed by humans, natural chemical reactions in the body lead to the formation of resveratrol metabolites, which most cells are then exposed to, apart from the cells lining the digestive tract. This means that in cell culture studies, concentrations of resveratol are often 10 to 100 times higher compared to concentrations observed in human plasma after individuals have orally consumed resveratrol.

When given orally as a pill, studies show that about 70% of the resveratrol dose is absorbed. However, bioavailability of resveratrol is relatively low. In a study where subjects were given a 25mg oral dose of resveratrol, only trace amounts of unchanged resveratrol (below 5 ng/ml) could be detected in plasma, due to its rapid metabolism and elimination. The metabolism takes place in the intestines and liver into conjugated forms of glucuronate and sulfonate. The resveratrol metabolites that are most abundant in humans, rats, and mice are trans-resveratrol-3-O-glucuronide and trans-resveratrol-3-sulfate.

Some researchers believe that resveratrol accumulated in epithelial cells along the aerodigestive tract and potentially active resveratrol metabolites may still produce cancer-preventive and other effects. Others have found that even very large doses of resveratrol (2.5 and 5g) do not reach concentration levels in the blood that are necessary for preventing cancer. In a study published in the journal Clinical Biochemistry in 2002, researchers reported that the potential resveratrol health benefits based upon the in vitro activities of unconjugated resveratrol are unrealistic and greatly exaggerated. They proposed that further investigations into the benefits of resveratrol should focus on its glucuronide and sulfate conjugates.

SRT-501 is a proprietary formulation of resveratrol developed by Sirtris Pharmaceuticals, containing extremely high doses (3-5 g) of resveratrol. It is worth noting that in humans given SRT-501, the concentration of resveratrol in the blood reached levels necessary to produce effects on par with those resulting from animal and in vitro experiments. In a human trial, SRT-501 was found to significantly lower glucose levels in diabetic patients.

It has been found that buccal delivery is the most efficient way of consuming resveratrol. Buccal delivery is direct absorption of the substance through the inside of the mouth, without swallowing it. A study published in August 2002 found that after 1mg of resveratrol in a 50ml solution was retained in the mouth for one minute before swallowing, 37ng/ml of resveratrol was measured in the blood two minutes later.