Olive oil protects against breast cancer, study finds

Four spoons of olive oil per day reduce the risk of suffering breast cancer by 66%, according to a Spanish study led by Professor Miguel Ángel Martínez-González, a head of department in the faculty of medicine at the University of Navarra.

The results published in the Journal of the American Medical Association, or JAMA, confirm the importance of one cornerstone of the Mediterranean diet.

The study began in 2003 with 7,447 participants from seven of Spain’s 17 autonomous communities. It first looked at cardiovascular disease and then later focused on breast cancer.

Regarding cardiovascular disease, researchers found that 37 grams of olive oil daily reduced the possibility of suffering from this disease by 30%. The reason was the high content of monounsaturated fats and natural anti-oxidants such as Vitamin E and polyphenol, which has a positive effect on cholesterol.

In the most recent part of the study thousands of Spanish families were provided with a litre of extra virgin olive oil every week for five years. Researchers monitored 4,282 women who had identical characteristics except for their diet.

The women, aged between 60 and 80, were divided into three groups: the first had a diet that was rich in olive oil (50 grams daily); the second had a diet that was rich in dried fruits (30 grams of nuts and almonds daily) and the third followed a low fat diet.

Specifically, the results showed that over five years women who had four spoons of olive oil each day had their risk of breast cancer cut by two-thirds. Those who ate more nuts and followed a low fat diet, however, did not show any statistically significant results.

"The primary focus of the research was on people with cardiovascular disease,” Martínez-González explained, “and the cancer study was secondary.” Extra virgin olive oil was chosen because it has more polyphenol. The oil was provided directly to the participants. "We assured ourselves that they had it by giving it to them free each week,” he said.

Martínez-González explained that in experiments with animals the polyphenol in extra virgin olive oil had already demonstrated its capacity to detain the advance of cancer.

The PREDIMED (prevention with a Mediterranean diet) research specifically excluded patients who were already diagnosed with breast cancer, but Martínez-González believes it would be interesting to evaluate the effect of olive oil in patients who have already been diagnosed with tumours. He argues that in any case the results are so strong that all patients should include it in their diet.

One potential weakness in the study was that only 35 cases of breast cancer were diagnosed across all the groups (compared to the 41 that would otherwise be expected), which means that small variations between the three groups had greater statistical importance. Another possible flaw was that the women knew what they were taking; there was no double blind control.

Despite these caveats it is interesting to compare Spain with other European countries. Eastern European countries do not follow a Mediterranean diet but they nonetheless have lower incidences of breast cancer. Bosnia, Moldavia and Ukraine have a lower incidence than Greece, for example, though the researchers believe this may be due to poor levels of diagnosis.

On the other hand, women in the city of Jaén, which is the main producer of extra virgin olive oil in Spain, have the lowest levels of breast cancer in the country.

Breast cancer has increased by 20% worldwide since 2008, according to the JAMA study.

The PREDIMED study now moves on to analysing the benefits of olive oil in other types of cancer.