Scientists from Puleva Biotech and the Spanish Consejo Superior de Investigaciones Científicas (CSIC) report that hydroxytyrosol was rapidly absorbed when provided as an aqueous supplement.

However, the levels of hydroxytyrosol absorbed were relatively low and a large number of metabolites were produced, according to findings of a study with 10 healthy volunteers published in Pharmacological Research​.

Of the low levels of the olive compound measured, the researchers note that over 50 per cent of this was detected in LDL-cholesterol fractions, said the researchers, led by CSIC’s Eduardo Lopez-Huertas.

“The transient association with LDL observed in plasma may have physiological implications but more research is needed using larger intervention trials with different hydroxytyrosol and formulations that render hydroxytyrosol more bioavailable before any conclusion can be made,”​ wrote the researchers.

Hydroxytyrosol is thought to be the main antioxidant compound in olives, and believed to play a signficant role in the many health benefits attributed to olive oil. Previous research by a team from the University of Barcelona found that LDL or 'bad' cholesterol levels could be cut substantially after consuming just 25 millilitres of virgin olive oil daily for one week. Other studies have suggested that it could also protect against cancer. Data has also suggested the compound may boost eye health and reduce the risk of against macular degeneration.

“Natural antioxidants are a main target for the nutraceutical industry,”​ wrote the researchers. “These results should provoke discussion concerning the number of commercially available products in the form of capsules of olive oil extracts, or olive oil antioxidant supplements, which try to mimic the antioxidant effects of virgin olive oil.”​

Study details​

Huertas and his co-workers investigated the absorption of 99.5 per cent hydroxytyrosol in an aqueous solution in 10 healthy volunteers. The dose used was 2.5 mg per kg of body weight. “The dose used in the study (2.5 mg/kg or 175mg for a 70 kg subject), is well above the nutritional amounts of hydroxytyrosol present in virgin olive oil, but in line with the estimated intake of polyphenols in the diet from foods like coffee (200 mg/day),”​ explained the researchers.

The maximum blood levels for hydroxytyrosol and its metabolite homovanillic alcohol were detected after 13 and 16.7 minutes, respectively. Moreover, analysis of LDL fractions in the blood showed that pure hydroxytyrosol transiently associated with LDL lipoproteins

“The association of hydroxytyrosol with LDL, although brief, may be relevant in the context of the physiopathology of atherosclerosis, as oxidised/ modified LDL trapped in the arterial intima seem to trigger early events of the process,” ​wrote the researchers.

“This association is likely to be prolonged in the case of hydroxytyrosol administered in olive oil due to its higher bioavailability,”​ they added.

Source: Pharmacological Research​

Volume 61, Issue 4, Pages 364-370

“Human absorption of a supplement containing purified hydroxytyrosol, a natural antioxidant from olive oil, and evidence for its transient association with low-density lipoproteins”​

Authors: M. Gonzalez-Santiago, J. Fonolla, E. Lopez-Huertas