Glutamic acid linked to lower blood pressure

Glutamic acid may be one of the components responsible for the lower blood pressures of people with vegetable-rich diets, according to a study published in Circulation, journal of the American Heart Association. Glutamic acid is a major component of protein; vegetable protein contains higher levels of glutamic acid than animal protein.

Previous research by the authors, from Imperial College London and Northwestern University, Chicago, in collaboration with other institutions in the US, Japan and China, showed that people with more vegetable protein in their diet tend to have lower blood pressure. The new research suggests that glutamic acid may be one of the components of vegetable protein linked to lower blood pressure.

The researchers looked at diet and blood pressure data from over 4,000 people. They analysed the amount of five amino acids in people’s diets and found that, on average, people who consume more glutamic acid have lower blood pressure than those who consume less.

Dr Ian Brown, co-author of the study from the Department of Epidemiology and Public Health at Imperial College London, said: "After we observed that vegetable protein in the diet was linked to lower blood pressure, we wanted to know what elements of vegetable protein might be responsible. Our new research suggests that glutamic acid may partly explain the link between vegetable protein and lower blood pressure."

"The next steps will be to reproduce this finding in other studies, and investigate how glutamic acid might exert an effect on blood pressure. However, there is no ‘magic bullet’ for preventing high blood pressure, and vegetable protein and glutamic acid are individual elements of a broader healthy eating pattern," added Dr Brown.

The new study is in line with findings from the DASH diet, developed by the US National Institutes of Health and recommended by the American Heart Association. Proven to lower blood pressure, the diet is rich in fruit, vegetables and low-fat dairy products, as well as whole grains, lean poultry, nuts and beans – many of which are naturally high in glutamic acid.

The researchers analysed data from 4,680 people aged 40–59, from the UK, USA, Japan and China. Participants were involved in the study for around three weeks, between 10 and 13 years ago. During their first visit to the clinic, participants completed a thorough questionnaire and interview about their daily food intake, gave a urine sample and had their blood pressure taken. The participants returned to the clinic the next day for a second questionnaire, interview and blood pressure reading. This process was repeated two to three weeks later.

The scientists calculated the amount of five different amino acids in the participants’ diets and correlated amino acid levels with blood pressure. People with a higher proportion of glutamic acid in the protein they consumed (4.7%), had, on average, lower systolic blood pressure (by 1.5–3.0 mmHg) and lower diastolic blood pressure (by 1.0–1.6 mmHg).

Professor Paul Elliott, one of the authors of the study from the Department of Epidemiology and Public Health at Imperial College London, said: "A person with high blood pressure might have a reading of 140 mmHg, so at first sight these differences don’t look like much. However, from a population perspective this is important. High blood pressure is a risk factor for cardiovascular disease, so if we can reduce the population’s blood pressure by just 1–2 mmHg, we could reduce overall risk of heart disease."

"Many dietary factors can have small effects on blood pressure. In combination, these effects can become clinically relevant. We hope our research will help to develop optimal diets and advice to prevent and control high blood pressure, and reduce the burden of cardiovascular disease," added Professor Elliott.

(Source: Imperial College London: Circulation: July 2009)