Researcher Dr Emad Al-Dujaili from Queen Margaret University looked at how a daily dose of pomegranate juice might affect blood pressure. The study consisted of 20 participants: 10 took a daily dose of 500ml pomegranate juice and 10 took a placebo of 500ml water. Measurements of blood pressure and urinary hormone levels were taken before and after 30 minutes of exercise, both before starting the study and one week after pomegranate juice.
People who drank the pomegranate juice showed significant improvements in blood pressure after one week, whilst those in the placebo group showed no significant difference in any variable. After one week of daily pomegranate juice consumption, systolic blood pressure levels were lowered both before and after exercise (pre-exercise: 141±20.7 to 136.1±17.3mmHg, p=0.03 and post-exercise:156.4±17.5 to 149.5±10.2mmHg, p=0.04) as were diastolic blood pressure levels (90.9 ±11.6 to 87.1±8.7mmHg, p=0.04 and 102.6±23.9 to 94.6±20.4mmHg, p=0.05).
The ratio of cortisol to cortisone in the urine also dropped after a week of pomegranate juice consumption (1.81 ±1.24 to 0.82 ±0.56, p=0.009). Cortisol is an active steroid hormone, produced from cholesterol in the adrenal glands, which affects glucose and fat metabolism and can increase blood pressure by altering salt and water balance in the kidneys and colon. In contrast, cortisone is an inactive metabolite of cortisol which exerts no known physiological actions. The inter-conversion of active cortisol and inert cortisone is mediated within organs such as the liver and kidneys by enzymes called 11β-hydroxysteroid dehydrogenases. The decrease in the urinary cortisol to cortisone ratio suggests that compounds present in pomegranate juice may have modified cortisol-cortisone metabolism by these 11β-hydroxysteroid dehydrogenase enzymes.
This is the first time that pomegranate juice has been shown to have a positive effect on blood pressure both before and after exercise. However, this was only a small study on healthy volunteers and the findings need to be validated by a larger trial.
Researcher Dr Emad Al-Dujaili, Senior Lecturer at Queen Margaret University said:
"Blood pressure is controlled by a complicated interaction between hormones, the nervous system and the physical properties of blood and blood vessels. Our study shows that pomegranate juice may have the potential to lower blood pressure levels both at rest and following exercise. Whilst the effects that we found were slight, they do give us an insight into how pomegranate juice and the hormone cortisol can alter this system in the human body to give health improvements.
"Our study was only on a small number of healthy volunteers, so the next step is to see if pomegranate juice might have similar effects on people with high blood pressure, a known risk factor for heart disease and stroke. We also want to look at whether pomegranate juice has an effect on other areas where glucocorticoids are known to play a part, such as BMI, fat distribution and insulin resistance."
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