Authors: Professor Clare Collins, Associate Professor Tracy Burrows and Dr Tracy Schumacher
High blood pressure is called the silent killer. That’s because it has no symptoms. Having high blood pressure (hypertension) increases your risk of heart disease, stroke, heart failure and kidney disease.
Six million Australian adults (34%) have high blood pressure – 140/90 millimetres of mercury (mmHg) or more – or take medications for it. Of those, four million have high blood pressure that isn’t treated or under control.
No wonder heart disease and stroke directly cost the Australian economy A$7.7 billion a year.
There is some good news. High blood pressure can be treated or prevented. Eating oats, fruit and vegetables – and beetroot, in particular – helps. So does avoiding salt, liquorice, caffeine and alcohol.
Optimal blood pressure is 120 mmHg or less over 80 mmHg or less. Lowering it by 1-2 mmHg can have a big impact on reducing your risk of heart disease and stroke, and the nation’s health care costs.
A review with five research trials included tested the impact of oats on systolic blood pressure (the first blood pressure number, which is the pressure at which the heart pumps blood) and diastolic blood pressure (the second number, which is when the heart relaxes) in about 400 healthy adults.
The researchers found that systolic blood pressure was 2.7 mmHg lower and diastolic blood pressure was 1.5 mmHg lower when participants ate around 60 grams of rolled oats (a packed half-cup raw oats) or 25 grams of oat bran per day.
This quantity of oats or oat bran contains around four grams of a type of fibre called beta-glucan.
For each extra one gram of total daily fibre, there was an extra 0.11 mmHg reduction in diastolic blood pressure.
Recommended minimum daily adult fibre intakes are 30 grams for men and 25 grams for women.
While some of fibre’s effect is due to weight loss, soluble fibres produce bioactive products when they’re fermented in the large bowel. These work directly to lower blood pressure.
To improve your blood pressure, eat rolled oats or oat bran for breakfast, add to meat patties, or mix with breadcrumbs in recipes that call for crumbing.
Beetroot is extremely rich in a compound called inorganic nitrate. During digestion, this gets converted into nitric oxide, which causes arteries to dilate. This directly lowers the pressure in them.
A review of 16 trials of mostly healthy young men found drinking beetroot juice was associated with a 4.4 mmHg reduction in systolic blood pressure. But it found no change in diastolic blood pressure.
However a recent trial in 68 adults who already had high blood pressure found beetroot juice reduced systolic and diastolic blood pressure.
The men were randomly assigned to drink 250ml (one cup) of beetroot juice daily for four weeks or a non-active placebo.
Blood pressure in the men who drank the beetroot juice reduced over 24 hours, with systolic blood pressure 7.7 mmHg lower and diastolic blood pressure 5.2 mmHg lower.
Try wrapping whole fresh beetroot in foil and baking in the oven until soft, or grate beetroot and stir-fry with red onion and curry paste and eat as a relish.
Vitamin C, or ascorbic acid, is found in fresh vegetables and fruit. An average serve contains 10-40mg of vitamin C.
In a review of 29 short-term trials of vitamin C supplements, people were given 500 mg of vitamin C per day for about eight weeks.
Blood pressure significantly improved, with an average reduction in systolic blood pressure of 3.84 mmHg and 1.48 mmHg for diastolic blood pressure.
When only those with existing high blood pressure were considered, the drop in systolic blood pressure was 4.85 mmHg.
However, those at risk of kidney stones need to be cautious about taking vitamin C supplements. Excess vitamin C is excreted via the kidneys and can contribute to the formation of kidney stones.
One advantage of getting more vitamin C from eating more vegetables and fruit is that you boost your potassium intake, which helps counter the effects of sodium from salt.
Salt or sodium chloride has been used to preserve foods and as a flavour enhancer for centuries.
High salt intakes are associated with higher blood pressure.
Adults need between 1.2 to 2.4g of salt each day (one-quarter to a half teaspoon), which is equivalent to 460 to 920mg of sodium.
But in Australia seven out of ten men and three in ten women eat way more than that – and much more than the upper recommended limit of 5.9 grams of salt (about one teaspoon) or 2,300 mg of sodium per day.
If you add salt to food yourself this pushes your sodium intake even higher.
A review of studies involving 3,230 people showed that reducing salt intakes by 4.4 grams a day could reduce systolic blood pressure by about 4.2 mmHg and diastolic by 2.1 mmHg.
In those who had high blood pressure there were even bigger reductions of 5.4 mmHg (systolic) and 2.8 mmHg (diastolic).
Avoid foods high in sodium. Don’t add salt and try to choose lower-salt versions of processed foods.
Consuming one or more alcoholic drink a day is associated with systolic blood pressure that is about 2.7 mmHg and diastolic blood pressure 1.4 mmHg higher than non-drinkers.
Interestingly, when you first drink an alcoholic beverage, blood pressure goes down, only to rise later.
A rise in blood pressure after drinking alcohol is more likely to happen when you’re awake, rather during sleep.
The bad news is that larger amounts of alcohol increase your risk of high blood pressure, especially in men, but also to a lesser extent in women.
High blood pressure due to eating black liquorice is rare, but case reports have occurred.
Most liquorice candy sold currently contains very little true liquorice root and therefore, little glycyrrhizic acid (GZA), the active ingredient.
Occasionally, liquorice candy does contain GZA in large amounts. GZA causes sodium retention and potassium loss, which contributes to high blood pressure.
So check liquorice food labels. Take care if it contains liquorice root.
Caffeine is most commonly consumed in coffee, tea, cola and energy drinks.
High intakes of caffeine from coffee increase blood pressure in the short term.
In a review of five trials, people given one to two cups of strong coffee had an increase in their systolic blood pressure of 8.1 mmHg and 5.7 mmHg for diastolic blood pressure, up to about three hours after drinking it.
But three studies that lasted two weeks found drinking coffee did not increase blood pressure compared with decaffeinated coffee or avoiding caffeine. So you need to monitor your individual response to caffeine.