Milk Thistle Extract

What is milk thistle extract?

The milk thistle plant Silybum marianum is a flowering herb native to the Mediterranean region that is now widespread throughout the world (R). The extract of its seeds, called silymarin, has been used as a traditional herbal remedy for nearly 2000 years (R).

Silymarin is a complex containing flavonolignans including silybin, silydianin and silychristin, and flavonoids such as taxifolin that together comprise 65-80% of milk thistle extract, with the remaining being fatty acids and polyphenolic compounds. The most abundant component in silymarin is silibinin, a 1:1 mixture of silybin A and silybin B (R) that makes up 50-70% of silymarin (R).

Is milk thistle extract stable?

Silymarin microemulsions have been shown to be physically stable, maintaining their physical appearance even after multiple heating and cooling cycles where they were stored at 4°C for 2 days, then 45°C for another 2 days per cycle. Chemically, silymarin can undergo oxidative degradation, which can be prevented by incorporating silymarin in oil-in-water microemulsions so that it is protected in the internal oil phase by the external aqueous phase acting as a barrier for oxygen diffusion (R). In another study, the stability of the compounds in a silymarin cream was over 90% after storage at 25°C and 40°C for 6 months (R).

Does milk thistle extract get absorbed?

Silibinin, silydianin and silychristin in silymarin were all readily absorbed by intact mouse skin in both in vitro and in vivo experiments. Silibinin had the highest absorption due to its lipophilicity and structure, compared to silychristin which has an additional hydroxyl group that makes it more hydrophilic, and silydianin which has a cyclic ketone moiety that increases its molecular volume, hindering its penetration of the skin (R). Silymarin has also been shown to penetrate the skin of rabbits (R). Similarly, 2 studies on human skin showed that topical application of silymarin can deliver appreciable amounts of its constituents into the skin (R, R).

Transdermal devliery of a silymarin solution was not observed in a study using the abdominal skin of newborn pigs (R), but a different study found that significant amounts permeated across human cadaver skin (R).

Penetration enhancers such as lecithin, propylene glycol and peptide dendrimers can be used to increase the skin delivery of milk thistle extract (R, R, R).

What happens after milk thistle extract is absorbed?

The compounds in silymarin appear to be metabolised after topical application (R).