To help investigators understand the effects of dietary nitrate supplementation on the ability to exercise in COPD patients, the investigators will recruit 15 people with mild to moderate disease. They will complete a series of undemanding exercise tests on three separate occasions. On one occasion they will have had a course of nitrate rich beetroot juice leading up to the tests, and on the other occasion they will have had a course of beetroot juice with the nitrate removed. The investigators will monitor blood pressure, levels of nitrate and nitrite in the blood, oxygen uptake and functional capacity during the tests which will allow us to assess any effects that may have occurred as a result of increased nitrate intake.