Behind the Headlines

Monday December 22 2008

Olive oil features highly in the Mediterranean diet

“Olive oil contains tumour-killing chemicals that may help us to win the war against breast cancer,” the Daily Express reported. The newspaper suggested that premium extra virgin olive oil contains tumour-killing chemicals that make breast cancer cells self-destruct. According to the report, a study has shown that the substances in the oil work in a similar way to the drug Herceptin by reducing the concentration of HER2 protein that helps HER2-positive breast cancer to grow.

The story is based on a laboratory study in which researchers extracted phenols from commercially available extra virgin olive oil and assessed their effects on HER2-positive breast cancer cells. They found that the phenols from the oil reduced the levels of HER2 protein and also increased tumour cell death. These findings will be of interest to the scientific community, but it is important for large, epidemiological studies (in humans) to establish whether a Mediterranean diet – including high intake of olive oil – can protect against breast cancer.

Where did the story come from?

Dr Javier Menendez and colleagues from the Catalan Institute of Oncology and other medical and academic institutions in Catalonia, Spain, carried out this study. The research was supported by a grant from the Instituto de Salud Carlos III. A provisional version of the study is available in the BMC Cancer medical journal.

What kind of scientific study was this?

HER2 is a protein found on the surface of some cancer cells, including breast cancer. This protein can bind to another molecule (known as human epidermal growth factor), which then encourages the growth and division of the tumour cells. Not all breast cancers have the HER2 protein on their surface; it is estimated that one in five women with breast cancer will have HER2 receptors.

In this study, the researchers investigated the effects of olive oil on breast cancer cells grown in laboratory cultures. Using a method called solid phase extraction, they removed and purified certain chemicals called phenols from commercially available extra virgin olive oil. These were then added to the growth medium for HER2-positive and HER2-negative breast cancers to see what effect they had on the tumour cells.

Several laboratory tests were then carried out to determine how fast the tumour cells were growing, their metabolic activity, whether the phenol caused cell death, whether the phenol had an effect on levels of HER2 protein and whether or not HER2 protein was activated in the presence of the phenol. The results from these tests were compared with those from tests performed on breast cancer cells that were not cultured with the phenols.

What were the results of the study?

The researchers found that some single phenolic compounds (including hydroxytyrosol, tyrosol and others) and all the polyphenols (several phenols joined together) from extra virgin olive oil induced “strong tumouricidal effects” in breast cancer cells that had HER2 protein on their surface. The phenols also reduced the levels of HER2 protein and its activation.

What interpretations did the researchers draw from these results?

The researchers conclude that the phenols in extra virgin olive oil have the ability to cause degradation of the HER2 protein on breast cancer cells. This may mean they can be used as a basis for the design of new HER2-targeting agents.

What does the NHS Knowledge Service make of this study?

This study found that phenols extracted from extra virgin olive oil have an effect on HER2-positive breast cancer cells grown in culture in the laboratory.

When purified, the phenols that had been extracted from commercially available extra virgin olive oil affected breast cancer cell proliferation and survival in cultures. This property may partly help to explain why an olive oil-rich Mediterranean diet may offer some protection from malignancies, although the researchers report that the results about this protective effect are conflicting. This is an important point: the researchers acknowledge that large, epidemiological studies (in human populations) have found conflicting results about whether a Mediterranean diet can protect against breast cancer.

When considering how these findings can be used in a practical application, it should be noted that there may be differences in how tumour cells react to chemicals applied directly in the laboratory and how they respond to lower concentrations in real life. There is also the possibility that these chemicals may have other side effects in humans.

These findings will be of interest to the scientific community, but there remain several important steps in researching this approach before it is confirmed that a diet rich in olive oil can protect against breast cancer.







Analysis by Bazian

Edited by NHS Choices

Links to the headlines

How olive oil can help in breast cancer fight. Daily Express, December 22 2008

Links to the science

Menendez JA, Vazquez-Martin A, Garcia-Villalba R, et al. Anti-HER2 (erbB-2) oncogene effects of phenolic compounds directly isolated from commercial Extra-Virgin Olive Oil (EVOO). BMC Cancer 2008, 8: 377

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