Tossing a salad in olive oil dressing may be one way to keep blood pressure under control, a study suggests.

The combination of unsaturated fat and nitrate-rich lettuce and celery suppresses an enzyme in the body linked to high blood pressure, or hypertension, scientists have found.

Previous research has shown that a Mediterranean diet can help reduce blood pressure. Typically, a Mediterranean diet includes unsaturated fat from olive oil, avocados and nuts, along with vegetables high in nitrite and nitrates including spinach, celery, carrots and lettuce.

The new study, conducted on mice, showed that nitro-fatty acids formed when these foods come together in the body can combat hypertension. Nitro-fatty acids were found to inhibit the enzyme epoxide hydrolase, which is known to raise blood pressure.

Sanjay Thakrar, from the British Heart Foundation, which co-funded the research published in the journal Proceedings of the National Academy of Sciences, said: “This interesting study goes some way to explain why a Mediterranean diet appears to be good for your heart health. The results showed a way in which a particular compound could combat high blood pressure, which is a major risk factor for heart disease.

“However, more work is necessary as these experiments were conducted in mice and this compound could also be having its effect through other pathways.”

The British and US study authors, led by Philip Eaton from King’s College, London, studied mice genetically engineered to resist the effects of nitro-fatty acids on epoxide hydrolase. Unlike unmodified animals, the mutant mice were not protected from high blood pressure.