Dose-response Effect of Dietary Nitrate on Muscle Function in Older Individuals

Overview

Nitrate is a naturally-occurring substance found in foods, especially green leafy vegetables and beets. Increasing nitrate intake (by drinking beetroot juice (BRJ) has been shown to improve muscle function young and middle-aged subjects, athletes, and patients with heart failure. The purpose of this study is to determine whether dietary nitrate provides a similar benefit in older individuals, and if so, the optimal dose. We will be comparing the effects of ingesting BRJ containing a smaller or greater amount of nitrate versus the effects of a placebo (BRJ from which the nitrate has been removed).

This study consists of four visits that will take a minimum of 15 days to complete. Study Visit One (Screening) 1-2 hours The purpose of the screening visit is to explain all aspects of the study. The investigators will also determine if individuals can participate in the study. Eligible subjects will undergo a complete medical history and physical exam. They will have their blood drawn, and will provide a urine sample (to determine if they are pregnant). Subjects will also practice the entire neuromuscular function exercise test. During this test, the strength of the subject's muscles will be determined by having them kick, push and/or pull back as hard as they can while their leg is strapped to an exercise device. Blood pressure and heart rate and rhythm will be monitored. Subjects will be instructed to consume their normal diet throughout the study. However, they will be asked to avoid eating foods high in nitrate such as beets, spinach, and collard greens the evening before each visit. They will be asked to refrain from the use of antibacterial mouthwash, such as Listerine or Cepacol, during the study. Subjects will also be asked to not chew gum or to consume alcohol or food and drinks that contain caffeine for 24 hour before each visit. This includes coffee, tea, chocolate and soft drinks such as Mountain Dew. Finally, they will be asked to fast for 12 hour prior to each study visit. Study Visit Two - Approximately 5 hours At the beginning of this visit a catheter (small, flexible, sterile plastic tube) will be placed through a vein in one of the subject's arms. This is for collection of blood samples. Blood will be drawn four times during this visit. Each draw will be 6mL or about 1.2 teaspoons. The first blood draw will check nitrate and nitrogen levels. Subjects will then have a breath test to check nitric oxide. They will then drink about 280 mL (about 1 cup) of BRJ. In one trial, this will be a placebo, that is, BRJ from which the essentially all of the nitrate has been removed. In another trial, they will drink BRJ still containing nitrate. In a third trial, they will drink an equal mixture of the placebo and nitrate-containing BRJ. Blood and breath samples will be obtained every hour. Heart rate and blood pressure will be measured at the same times the blood and breath samples are obtained. About 2 hours after ingestion of BRJ (or placebo) subjects will be asked to perform the neuromuscular function test that was practiced during the screening visit. After completing the exercise test one final blood and breath sample will be obtained. Study Visits Three and Four The same procedures completed during Study Visit Two will be performed. The order of treatment (placebo vs. lower dose vs. higher dose of nitrate) will be randomized using a computer program. Neither the subjects nor the investigators will know the treatment they receive during each visit until the entire study is completed.