A 12-week course of daily beetroot juice supplement for people with chronic obstructive pulmonary disease (COPD) lowered blood pressure and improved how far patients could walk in six minutes, according to research.

COPD -- a serious lung condition affecting around 400 million people worldwide -- includes chronic bronchitis and emphysema, causes breathing difficulties and severely limits people's capacity for physical activity. It also increases the risk of heart attacks and strokes.

The new research, published in the European Respiratory Journal, tested a concentrated beetroot juice supplement that is high in nitrate against a beetroot juice placebo that looked and tasted the same but had the nitrate removed.

"There is some evidence that beetroot juice as a source of nitrate supplementation could be used by athletes to improve their performance, as well as a few short-term studies looking at blood pressure,” said Professor Nicholas Hopkinson from Imperial College London, UK.

“Higher levels of nitrate in the blood can increase the availability of nitric oxide, a chemical that helps blood vessels relax. It also increases the efficiency of muscles, meaning they need less oxygen to do the same work," Hopkinson said.

The study included 81 people with COPD, and whose systolic blood pressure measured higher than 130 millimetres of mercury (mmHg).

Systolic blood pressure is the highest level the blood pressure reaches when one's heart beats, and the ideal range is between 90 and 120mmHg.

As well as monitoring patients' blood pressure, researchers tested how far patients could walk in six minutes at the beginning and end of the study.

Participants were randomly allocated to either receive the 12-month course of nitrate-rich beetroot supplement (70 ml of concentrated beetroot juice containing 400 mg of nitrate once a day) or the placebo.

Researchers found that those taking the nitrate-rich supplement experienced an average reduction in systolic blood pressure of 4.5mm/Hg compared to those taking the placebo.

There was also an average increase of around 30 metres in how far patients could walk in six minutes for those taking the nitrate-rich beetroot juice.

"At the end of the study, we found that the blood pressure of people taking the nitrate-rich beetroot juice drink was lower and their blood vessels became less stiff. The juice also increased how far people with COPD could walk in six minutes compared to placebo. This is one of the longest-duration studies in this area so far. The results are very promising, but will need to be confirmed in larger, longer-term studies," Professor Hopkinson said.

"COPD cannot be cured, so there is a pressing need to help patients live as well as they can with the condition and to reduce their risk of cardiovascular disease," said Professor Apostolos Bossios from the Karolinska Institutet in Sweden.

Bossios, who was not involved in the research, however, stressed the need to study patients for a longer duration to confirm the findings.