Can Drinking Water Lower Blood Pressure?
With high blood pressure affecting around one in three UK adults, it’s no wonder we’re constantly being fed headlines about some new, easy-to-implement solution to hypertension. If you’ve heard that drinking more water can lower blood pressure, read on – we’re going to set things straight and explain the link between hydration and blood pressure in a little more detail.
How does water impact blood pressure?
We all know drinking water is good for us. Water is the human body’s principal chemical component, making up between 50% and 70% of body weight. Every part of the body needs water to work properly – it gets rid of waste, regulates temperature, lubricates and cushions joints and protects sensitive tissues. It also impacts heart health and blood pressure.
Drinking water to raise low blood pressure
For years, it was believed that water did not affect blood pressure. In around 2000, researchers at Vanderbilt University Medical Center found that water actually raised blood pressure in patients who had lost their baroreflexes – the system that keeps blood pressure within a normal range.
Subsequent research found that it did this by increasing the activity of the sympathetic (fight-or-flight) nervous system, making subjects feel more alert, raising blood pressure and giving a temporary energy boost. The findings prompted the American Red Cross to conduct their own study into the link between drinking water and fainting, which found that drinking 16 oz of water (about 473 ml) before donating blood reduced the fainting response by 20%.
Dehydration, on the other hand, can be a cause of low blood pressure due to a decrease in the volume of blood circulating the blood vessels. A normal blood volume enables blood to reach all the tissues in the body, delivering oxygen and nutrients where they’re needed.
Drinking water to lower blood pressure
What about high blood pressure? Can drinking more water lower blood pressure readings? Similarly, it’s more a case of avoiding dehydration, which studies have shown to increase blood pressure. A study conducted in rats showed that recurrent dehydration can worsen hypertension.
High blood pressure is caused by the persistent high pressure of blood against the walls of arteries. It occurs when smaller blood vessels narrow, forcing the heart to work harder to push blood through the arteries.
According to researchers, the effect of dehydration on blood pressure is threefold:
- It causes the blood to become thicker due to reduced water content.
- It causes the kidneys to release renin, an enzyme that helps the body retain sodium and water to correct the low fluid volume.
- It causes the brain to release vasopressin, a hormone secreted when there’s a high amount of sodium in the blood, or when blood volume is low. High concentrations of vasopressin can cause the blood vessels to constrict.
If dehydration continues, the body maintains a higher blood pressure to ensure that vital organs receive the blood supply.
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How much water should you drink?
Official UK guidance recommends we drink 6 to 8 cups or glasses (1.5 to 2.5 litres) of fluids a day, and more in hot weather or when exercising or working hard enough to sweat. Fluids include water, milk, low-sugar drinks, and tea and coffee. Foods, such as tomatoes, melon and cucumber, soups and stews, and ice lollies and jelly, can also contribute to your fluid intake.
However, other sources say it’s not quite that clear cut. Harvard Medical School recommends that most people need about 4 to 6 cups of water a day, but stresses that ‘There’s no one-size-fits-all answer. Water intake must be individualized, and you should check with your doctor if you are not sure about the right amount for you.’ Other sources maintain that the body tells us what it needs, when it needs it: simply drink when you are thirsty.
If you’ve been diagnosed with hypertension, the best advice is to do your best to stay consistently hydrated to avoid spikes in blood pressure. Having a drink at mealtimes, and sipping water throughout the day or when thirsty, should be perfectly adequate for most.
While drinking more water isn’t going to lower high blood pressure overnight, it’s useful to understand why staying hydrated is so important to our overall health. A healthy fluid intake, alongside a balanced diet and active lifestyle, could make a big difference to those looking to better manage hypertension. You can find plenty more articles on the role of diet in controlling blood pressure in our resource hub.
Disclaimer: If you are concerned about your blood pressure, it is best to speak to your doctor. They can advise on the best way to manage your blood pressure and whether drinking water may be beneficial.
Blood pressure facts and figures, 2020 – https://www.bloodpressureuk.org/news/blood-pressure-facts-and-figures
Water: How much should you drink every day?, October 12, 2022 – https://www.mayoclinic.org/healthy-lifestyle-water
Water’s unexpected role in blood pressure control, July 14, 2010 – https://www.sciencedaily.com/releases-100706150639
Chronic recurrent dehydration associated with periodic water intake exacerbates hypertension, September 22, 2016 – https://www.ncbi.nlm.nih.gov/articles-PMC5032121
The eatwell guide, November 29, 2022 – https://www.nhs.uk/live-well/the-eatwell-guide
How much water should you drink?, May 15, 2022 – https://www.health.harvard.edu/how-much-water-should-you-drink
The truth about hydration, January 27, 2020 – https://www.theguardian.com/lifeandstyle/the-truth-about-hydration-should-you-drink-eight-glasses-of-water-a-day