None listed
Conditions
Brief summary
There is now consistent and convincing evidence that dietary inorganic nitrate plays an important role in the physiological control of blood pressure. Clinical trials have established that an increase in nitrate intake, either from supplements or vegetables, results in a dose-related decrease in blood pressure in healthy normotensive individuals. This trial will address the question: "Can ingestion of a diet high in nitrate lower blood pressure in treated hypertensive individuals?"
Interventions
A randomised, controlled, cross-over designed trial will be performed. Each participant will complete 2 intervention periods of 1 week each in random order. These will be separated by a 2 week washout period. The two 1 week intervention periods will correspond to:
1. Active – high nitrate intake: consumption of 1X70 ml/d (35 ml with breakfast and 35 ml with dinner) of a concentrated beetroot juice beverage containing approximately 200 mg of nitrate per dose (400 mg total for the day)
2. Placebo
A randomised, controlled, cross-over designed trial will be performed. Each participant will complete 2 intervention periods of 1 week each in random order. These will be separated by a 2 week washout period. The two 1 week intervention periods will correspond to: 1. Active – high nitrate intake: consumption of 1X70 ml/d (35 ml with breakfast and 35 ml with dinner) of a concentrated beetroot juice beverage containing approximately 200 mg of nitrate per dose (400 mg total for the day) 2. Placebo – control: consumption of 1X70 ml/d (35 ml with breakfast and 35 ml with dinner) of a concentrated beetroot juice containing <5 mg of nitrate (<10 mg total for the day) Participants and researchers will be blinded to treatment. The 400 mg dose of nitrate represents an upper level of nitrate intake achievable via dietary means. At the end of each 1 week intervention period, participants will collect a 24 h urine sample, then attend School of Medicine and Pharmacology Research Unit at Royal Perth Hospital in the morning (after a 12 h fast) for approximately 3 h. During this time: * A fasting blood sample will be collected for measurement of nitrate and nitrite concentrations, and biochemical markers related to vascular function. * Participants will then be provided with a standard low nitrate breakfast to be consumed over 20 minutes. * Participants will consume one 70 ml dose of the assigned beverage with breakfast. * An ambulatory blood pressure monitor will be fitted 30 minutes after breakfast. The monitor will record blood pressure every 20 min during the day and every 30 min overnight for the following 24 h. * A saliva sample will be collected 2 h after breakfast for measurement of nitrate and nitrite concentrations. * Participants will then go about normal daily activities, avoiding vigorous physical activity. * A second dose of the assigned beverage will be taken with dinner, and a third dose will be taken with breakfast the next morning. * For each participant, the timing of the visits will be on the same day of the week at the same time of day as far as possible. * Participants will return to the School of Medicine and Pharmacology Research Unit the next morning, after breakfast, to have the blood pressure monitor removed. In addition, daily throughout each 1 week intervention period participants will perform home blood pressure monitoring. These measurements will be performed between 2 and 3 hours after the dinner meal, shortly before going to sleep. Five home blood pressure measurements will be performed at this time each day. This will provide information regarding the time-course of any effects on blood pressure. Throughout the study period the background diet will be the participant’s usual diet.
Sponsors
The University of Western Australia
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Treatment
Masking
Blinded (masking used) (Subject, Caregiver, Investigator, Outcomes Assessor)
Eligibility
Sex/Gender
All
Age
50 Years to 70 Years
Healthy volunteers
No
Inclusion criteria
* Men and women will be aged between 50 and 70 years * Regular use of at least one antihypertensive medication for elevated blood pressure * Clinic/office systolic blood pressure will be >120 mmHg
Exclusion criteria
* Use of more than 3 antihypertensive medications * A change in antihypertensive medication within the past 1 month * Inability to attend clinic/office visits * Clinic/office systolic blood pressure greater than 160 mm Hg or less than 120 mm Hg; or diastolic blood pressure greater than 100 mm Hg; * Use of antibiotics (within previous 1 months); * current or recent (<6 months) smoking; * body mass index < 18 or > 35 kg/m2; * current cardiovascular or peripheral vascular disease, or diagnosed diabetes, or history of a cardiovascular event; * a psychiatric illness, or presence of other major illnesses such as cancer; * current or recent (within previous 6 months) significant weight loss or gain (> 6% of body weight); * alcohol intake > 210 g per wk for women and > 280 g per wk for men; * pregnant or lactating women; * inability or unwillingness to consume beverages provided.
Outcome results
None listed