It seems so harmless, and yet every year people are hospitalised and even die from drinking too much water. Just last month, a 35-year-old woman from Indiana collapsed and died after downing four 500ml bottles of water in just 20 minutes after becoming dehydrated on a family holiday.
The cause of death was given as hyponatraemia, a life-threatening condition which occurs when the body’s blood sodium concentrations drop to an abnormally low level. This is dangerous because sodium plays a critical role in regulating the amount of water that gets into the body’s cells.
Drinking excessive amounts of water can dilute sodium levels to the extent that the brain begins to rapidly swell with the excess fluid leading to confusion, seizures and coma.
This happened in the 1995 case of Leah Betts, who died shortly after her 18th birthday after taking an ecstasy tablet and subsequently drinking seven litres of water within 90 minutes.
Research studies have since identified ecstasy as a known risk factor for hyponatraemia for reasons that are still not fully understood.
According to David Rowlands, professor of nutrition at Massey University, New Zealand, one of the populations most at risk of hyponatraemia are endurance athletes such as ultra-marathon runners and Ironman triathletes.
“There have been some cases in some ultra-endurance sports where hyponatremia has been caused by large volumes of water or diluted sports drinks being consumed, more than six to eight litres of fluid,” he says.
“It used to be a problem at the Hawaii Ironman event, but I think they’ve gotten on top of that now with awareness and provision of more sodium-containing drinks at the aid stations.”
So, what are the safe limits for water consumption, and should we keep tabs on how much we’re drinking when it comes to other common beverages such as coffee or energy drinks?
What’s the healthy limit on water?
According to the US Centers for Disease and Control, you should not drink more than 1500 ml of water or other fluids, such as sports drinks, within an hour.
This works out as a limit of approximately six glasses or three 500ml bottles of Evian.
John Speakman, a biology professor at the University of Aberdeen, says that usually this would be difficult to exceed in practice because the body’s natural thirst and satiety reflexes would prevent you from drinking that much.
Cases tend to happen when people have either become excessively dehydrated through drinking alcohol or being outside in hot weather for many hours, or are already vulnerable because they are taking diuretic medicines for high blood pressure, which remove sodium from the blood.
“It’s difficult to over hydrate, you have to drink a lot of water,” says Speakman. “If people are drinking slightly more than they need on average, it’s not a big issue.”
But what about the minimum drinking requirements?
While most of us have heard of the eight glasses of water per day rule, an idea that goes back to the 1940s, this has only ever been based on relatively flimsy scientific evidence.
Last year, Speakman and an international consortium of scientists published far more precise estimates. “What we found was that in your mid-20s, men require about 1.5-1.8 litres per day, or six to eight glasses,” says Speakman.
“A woman in her mid-20s requires around 1.3 to 1.4 litres, so five to six glasses. This declines a little over the course of life and by the time you’re in your 70s and 80s, you only need around 1.2 litres per day because you’re less active.”
However if you exercise regularly in hot temperatures then your daily fluid requirements can be more than two litres.
The pros and cons of coffee
Research has increasingly shown that coffee can be good for us. But just as with water, it’s advisable not to have too much. Experts at Nutritank, which provides medical education to healthcare professionals on food, nutrition and lifestyle medicine, says that UK guidelines recommend no more than 200mg caffeine (two and a half cups on average) in one sitting, and not more than 500mg (five medium-sized cups) per day.
“Higher intakes of caffeine can increase anxiety, restlessness and cause gastrointestinal disturbances,” says Dr Ally Jaffee, NHS doctor and co-founder of Nutritank.
The NHS advise pregnant women against having more than two and a half cups of coffee per day, while some individuals are far more sensitive than others to the effects of caffeine, due to genetic variations.
“Drinking too much caffeinated coffee can cause heart palpitations for some individuals, in which case it’s best to avoid caffeine,” says Alice Benskin, nutrition education lead at Nutritank.
Benskin says that for people who are already living with high blood pressure, keeping caffeine consumption to a minimum is advisable, due to its blood pressure elevating effects.”
Keep fizzy drinks to a minimum
In 2022, Coca-Cola followed by Pepsi Max topped the lists of sales in UK convenience stores, but while they are among our favourite beverages, nutritionists advise us to stay away from fizzy drinks as much as possible.
“Fizzy drinks are not helpful for our health in any way, the science is very clear on this,” says Federica Amati, medical scientist and nutritionist at Zoe, the personalised health company.
“They either contain added sugar and are a cause of increased dental cavities, increased risk of obesity and Type 2 diabetes, or they are sweetened with artificial sweeteners, which have also been linked to increased metabolic disease risk and a negative impact on the gut microbiome.”
While you would have to be consuming between 12 and 36 cans of Diet Coke per day to exceed the World Health Organization’s safety limit for the artificial sweetener Aspartame, Amati says that numerous studies have linked regular consumption of fizzy drinks to health concerns. She points to a 2022 study in the European Journal of Nutrition, where Norwegian scientists identified an association between consuming sugary or artificially sweetened carbonated beverages during pregnancy, with an increased risk of childhood ADHD. “Whilst the occasional can of pop is nothing to worry about, making them a regular staple in our diet is best avoided,” she says.
Watch out for energy drinks
Nutrition experts are even more damning on energy drinks, with Nutritank pointing to research that has linked them with an increased risk of obesity, diabetes, cardiovascular disease, mental illness and sleep disorders.
“Energy drinks should be avoided entirely, as there is no safe recommended intake or limit,” says Benskin. “Some energy drinks contain as much as 505mg of caffeine per can, as well as added sugar and other additives.”
While these drinks are particularly popular with professions who work long hours or night shifts as a way of maintaining alertness and staying awake, they have been associated with poorer sleep quality.
“Research demonstrated that nurses who consumed energy drinks had poorer sleep quality and fewer sleep hours, compared with caffeine-only consumers and non-caffeine consumers,” says Benskin.
The problem with orange juice
While drinking orange juice might seem like a healthy choice, recently updated government guidelines have recommended keeping daily intake of fruit juices to a minimum.
“It’s important to remember that orange juice has high quantities of sugar,” says Nikita Patel, associate medical director and GP at Vitality.
Patel says that some commercial juice products also include added sugar, which lowers the nutritional value and causes spikes in blood sugar levels and a subsequent energy crash.
Patel explains that when fruits like oranges or apples are converted into juice, a lot of the fibre content, which is found in the fruit’s pulp, is removed. As a result, when you drink juice, you absorb the sugar at a much faster rate, which is less healthy for your body. Instead, rather than consuming shop-bought juice, doctors often recommend making it yourself, or simply just eating the whole fruit.
“Freshly squeezed or homemade orange juice is generally better than shop-bought versions, mostly because it retains more of the nutrients, pulp and fibre of the fruit,” says Patel.
“What’s more, it doesn’t contain added preservatives or sugars that processed juices are made up of.”
