None listed
Conditions
Brief summary
High blood pressure is a leading risk factor for mortality. Diet and lifestyle change, which can reduce the need for costly blood pressure medication, can have the largest potential impact on high blood pressure in the community. Large randomised controlled trials demonstrate that consumption of diets rich in plant foods (fruits, vegetables, legumes and whole grains) lower blood pressure. We propose that the amount and type of vegetables consumed is important for blood pressure, and that focused advice to consume nitrate-rich vegetables will result in lower blood pressure. Acute and very short-term studies clearly demonstrate that an increase in nitrate intake can significantly reduce blood pressure. The objective of this study is to establish if these effects on blood pressure are sustained over a 4 week period. In a separate investigation we also wish to determine if daily consumption of nitrate-rich vegetables can lower the cardiovascular response to stress. Secondary objectives of this study are to explore the role of nitrate-rich vegetables in improving blood vessel stiffness and cognitive function and mood.
Interventions
A randomised, controlled, cross-over trial will be conducted to investigate the effects of different types of vegetables on blood pressure and arterial stiffness.
Each participant will complete three intervention diets of 4 weeks each in random sequence. The first intervention diet will be preceded by a 4 week lead in (washout) period. The first, second and third intervention diets will be separated by a 4 week wash out period.
The intervention diets are:
1. High nitrate diet (~400 mg per day
A randomised, controlled, cross-over trial will be conducted to investigate the effects of different types of vegetables on blood pressure and arterial stiffness. Each participant will complete three intervention diets of 4 weeks each in random sequence. The first intervention diet will be preceded by a 4 week lead in (washout) period. The first, second and third intervention diets will be separated by a 4 week wash out period. The intervention diets are: 1. High nitrate diet (~400 mg per day) – with an increase in high-nitrate vegetables (lettuce – all types, spinach, rocket, Chinese leafy greens, other leafy greens, celery, and beetroot). This will involve the consumption of two blended high-nitrate vegetable juices each day: one before breakfast and one before dinner. 2. Low nitrate diet (~100-150 mg per day) – with an increase in low-nitrate vegetables (cauliflower, capsicum, sweet potato, cucumber, tomato, and parsnip). This will involve the consumption of two blended low-nitrate vegetable juices each day: one before breakfast and one before dinner. 3. Low nitrate diet (control diet, ~100 mg per day) – without an increase in vegetables. This will involve the consumption of two blended juice drinks without vegetables each day, matched in energy to juices in diets 1 and 2: one before breakfast and one before dinner. Participants will be provided with personal blenders and advised on which vegetables/ingredients to buy and blend themselves (all meals will be maintained as usual with the exception of limiting nitrate-rich vegetables where possible). Adherence to the intervention diets will be monitored using juice checklist diaries; food intake questionnaires; and blood, urine and saliva samples. Participants will attend 9 visits over a period of 6-8 months at the School of Medicine and Pharmacology Research Unit at Royal Perth Hospital.
Sponsors
The University of Western Australia
Study design
Allocation
Randomised controlled trial
Intervention model
Crossover
Primary purpose
Treatment
Masking
Open (masking not used)
Eligibility
Sex/Gender
All
Age
21 Years to 75 Years
Healthy volunteers
No
Inclusion criteria
Ambulant men and women; 21-75 years; and Systolic blood pressure 120-160 mm Hg.
Exclusion criteria
Systolic blood pressure less than 120 mm Hg or greater than 160 mm Hg; Diastolic blood pressure greater than 100 mm Hg; Diagnosed type 1 or 2 diabetes or fasting glucose greater than 7.0mmol/L; Consumption of a diet estimated to contain greater than 200 mg/day of nitrate (volunteers willing to limit nitrate-rich vegetables for a period of 4 weeks before their lead in visit may be included); Consumption of greater than or equal to 5 serves of vegetables per day; Being vegan or vegetarian; Body mass index less than 18.5 kg/m2 and body mass index greater than or equal to 35 kg/m2; Use of antihypertensive medication; Use of nitric oxide donors, organic nitrites and nitrates, sildenafil and/or related drugs; Use of antibacterial mouth wash (volunteers willing to cease using antibacterial mouth wash for a period of 4 weeks before their lead in visit may be included); Use of antibiotics (within previous 2 months); Current or recent (less than 12 months) smoking; History of symptomatic cardiovascular or peripheral vascular disease or chronic kidney disease; Recent history of a psychiatric illness or other major illnesses such as cancer; A change in drug therapy likely to influence blood pressure or major secondary outcomes within the previous 3 months, and/or the likelihood that drug therapy would change during the study; Current or recent (within previous 6 months) significant weight loss or gain (greater than 6% of body weight); Alcohol intake greater than 140 g per week for women or greater than 210 g per week for men and/or binge drinking behaviour; Reported participation in night shift work during the study period; Breastfeeding, pregnancy or planning of pregnancy; and Inability or unwillingness to follow the study protocol.
Outcome results
None listed