by Dr Harriet Holme26 Apr 2021
It is estimated more than 1 billion adults have high blood pressure, projected to increase to 1.5 billion by 2025 (1). High blood pressure, termed hypertension, often doesn’t cause noticeable symptoms, but if left untreated accounts for more than 9 million deaths annually (1).
A normal blood pressure is somewhere between 90/60mmHg and 120/80mmHg. A raised blood pressure even just outside this range at 135/85mmHg has been shown to double your risk of a heart attack. For every 10mmHg you can lower your blood pressure by, you reduce your risk of dying by 13% (2).
Hypertension is one of the most common modifiable risk factors for cardiovascular disease and death (1), how can diet help?
While the cause of high blood pressure isn’t always clear, there are things that can increase your risk such as:
Diet has an important role on the long-term risk of developing high blood pressure, which means that it may be possible to reduce your risk by optimising your diet. While we all know we should be eating less salt, there are other factors that also play a role.
The Approaches to Reduce Hypertension (DASH) is a specific diet designed to reduce hypertension (3) and studies have found it to be effective (4). This diet advocates a plant-focused diet with limited diary and meat, and is very similar to the Mediterranean diet. In contrast to the Mediterranean diet, low fat products are advised instead of full fat.
The DASH diet was founded on the concept that vegetarian diets are associated with lower risk of high blood pressure (3). This may be because vegetarian diets are more likely to be higher fibre with less saturated fat. Additionally, diets that contain higher potassium, such as those high in fruit, vegetables and legumes may be beneficial (see below).
Both the DASH and Mediterranean style diets share the foundations with most healthy diets of:
Salt, or sodium chloride, plays an important role in the control of blood pressure. It’s widely accepted that most people eat too much salt. Even if you don’t add salt to food, about 75% of the salt we eat is “hidden” in foods that don’t taste salty, such as most commercially produced bread, breakfast cereals and processed food such as ready meals, pasta, soups, and sauces.
The kidney plays an important role in balancing the amount of water and salt in your body. Water and salt are linked so that if you eat more salt, your kidneys keep hold of more water. This leads to a rise in your blood pressure, and over time can become sustained. Drinking more water can’t flush out salt or toxins, so it is important to reduce your intake of salt in the first place.
What are the Recommended Limits for Salt?
The British Dietetic Society recommended limits of salt intake are:
How can you reduce your salt intake?
To try to reduce your salt intake, add herbs and spices instead of added salt. With regards “hidden salt” try to eat whole food, avoiding processed food. Request less added salt in restaurants and also for take-aways.
Is gourmet salt better?
There are lots of different salts available, from basic table salt to more exotic pink Himalayan, kosher, or sea salt. While they contain slightly different nutrients, the quantities are so small as to be negligible, and fundamentally they all contain sodium chloride, which will increase your risk of hypertension.
Is salt always bad for your health?
Interestingly there is now research to show that a very low intake of salt might also cause hypertension (1). So it appears as though there is a “J” shaped curve, where too little or too much salt increases your risk of hypertension, with a sweet spot or healthier range in the middle. However, this middle ground is still relatively low, and for the vast majority of people, decreasing salt will still reduce cardiovascular risk (5).
There is also emerging evidence that a higher potassium might actually offset some of the harm of sodium chloride in salt. Foods rich in potassium are:
Several studies have shown a dose response relationship with fruit and vegetable intake and blood pressure(12). This means that the more fruit and vegetables you eat, the lower your risk of hypertension. However, there is evidence that the quality of your diet is also important, so just eating a plant-based diet full of vegan processed food is not helpful. Increasing the range of your fruit and vegetable intake, and including pulses such as beans, lentils and peas, has also been shown to reduce blood pressure.
There is mixed evidence that eating meat increases risk of hypertension. One study found that the type of meat mattered more that quantity, with unprocessed meat not influencing risk for hypertension whereas consumption of processed meat (five or more times per week) increased risk of hypertension by 17% (13). Processed meat is already associated with increased risk of bowel cancer, so choosing unprocessed meat would have additional health benefits too.
Beetroot powder is increasingly trendy to reduce blood pressure as it naturally contains relatively high levels of nitric acid, a natural vasodilator. While beetroots and the juice have limitations with taste preference, beetroot powder can be a more convenient form. It’s made by grinding dried beetroot into a powder.
While beetroot powder is more concentrated and has a higher level of antioxidants than fresh beetroot (6), it is easier to consume it in much higher quantities, which means ingesting higher levels of the natural sugars.
Nitrites have an important role related increased blood flow, gas exchange, mitochondrial efficiency, and strengthening of muscle contraction (7). They stimulate relaxation of the smooth muscles that encircle arteries and veins, leading to dilatation of the vessels, thereby lowering blood pressure. Nitrate medications area used for people with hypertension, heart disease and angina to increase blood flow (8).
In the short term, research combining 22 different trials found that beetroot juice significantly improved hypertension, but there isn’t the same evidence to support longer term effects (9).
While more research is needed to further understand the effects of beetroot powder longer term, it does appear to be relatively safe, with some possible benefit for hypertension. If you are pregnant or breastfeeding, taking beetroot supplements are best avoided as there isn’t sufficient safety information. Also large doses of beetroot are associated with an increased risk of kidney stones.
The evidence to support the benefits of garlic on high blood pressure is mixed; with some combined (meta) analyses finding a significant improvement of hypertension (10) while others found no effect (11). However, no adverse effects have been reported, so taking garlic might help you if you have hypertension, but is unlikely to be harmful.
Evidence of benefit of omega 3 fatty acids is mixed with large scale studies showing either no effect (14), or a small reduction in risk of hypertension (15). Omega 3 fats do have other health benefits though, are unlikely to do harm, and are easily incorporated into your diet by eating oily fish twice a week and seeds such as chia seeds, flaxseeds and nuts.
Flaxseeds contain a polyphenol compound called Secoisolariciresionol diglucoside (SDG), which has been found to reduce blood pressure in animal models (16). The data suggests that the SDG compound inhibits Angiotensin Converting Enzyme (ACE), thereby lowering blood pressure. There are already medications, which block this enzyme, called ACE inhibitors, which are established in the treatment of hypertension.
In one study flaxseed powder improved hypertension in pre-diabetic people, who had slightly raised sugar levels in the precursor stage to diabetes (17). The true value of flaxseed will hopefully be determined by a randomised double blinded trial currently recruiting people with hypertension who have yet to start medication.
Dr Harriet Holme (https://healthyeatingdr.com/)