How much water do we really need?
How much water should you really drink per day?
The notion of ‘the more, the better’ when it comes to water intake may be commonplace with some health experts supporting beliefs that you need to guzzle litre upon litre of water each day, even when you’re not thirsty. This begs the question… is there actually any benefit to doing so, or can you really get too much of a good thing?
There is no denying the importance of adequate hydration. Water is essential to life and has many roles to play within our bodies, accounting for around 60% of body weight [1]. About a third of this water is found bathing our cells (as ‘extracellular’ fluid), whereas the rest is found inside our cells (as ‘intracellular’ fluid).
Water is involved in a variety of metabolic reactions, as well as playing an important role in maintaining blood pressure, acid balance (pH), and body temperature. Water helps to lubricate joints, acts as a shock absorber for vital organs and helps to move substances around the body, distributing vital nutrients and gases, and removing waste products via the blood and other fluids.
How are water levels regulated?
Our bodies are clever in endless ways and keeping our water levels closely regulated is no exception.
Fluid balance is regulated by thirst, which is the body’s natural response to fluid depletion. Receptors (osmoreceptors) in an area of the brain known as the hypothalamus constantly monitor the concentration of dissolved substances in our blood. When the water content of blood goes down, the concentration of these substances increases. Osmoreceptors detect this change and send signals to the thirst centre in the brain, causing us to reach for a glass of water. This rebalances the composition or ‘osmolarity’ of our blood once again, and our thirst is quenched.
There are other mechanisms involved that also help to maintain fluid balance in our bodies. Dehydration causes a drop in blood pressure as blood volume decreases. This drop in blood pressure is detected by different receptors (baroreceptors) in arteries in our hearts. The heart responds by increasing the rate and strength of its contractions to raise blood pressure back to normal. At the same time, the kidneys release a hormone (angiotensin II) which stimulates thirst and the release of a second hormone (aldosterone) from our adrenal glands. Aldosterone acts at the kidney to increase the amount of water being resorbed back into the blood, reducing the amount of water we lose as urine.
What happens when the balance is thrown off?
As we’ve seen, the body works hard to regulate fluid levels, but illness, injury, drinking too much or too little can lead to imbalances with potentially fatal consequences. Although the human body can survive a relatively long time without food (weeks to months, depending on our reserves), we can only survive a few days without water.
Effects of dehydration
Dehydration happens when water loss exceeds our intake. Every single cell in our body needs water, so it is not surprising that the symptoms of dehydration are widespread, and the severity of symptoms is dependent on the degree of dehydration. Some of the most common consequences of dehydration are listed below, but there are (of course) many others.
Consequences of dehydration include:
Reduced physical performance
Dehydration during exercise is not uncommon and reduced physical performance has been observed with as little as 2% body weight loss from fluid. Mild dehydration has been associated with reduced endurance, reduced motivation, increased fatigue, increased perceived effort and an inability to regulate our body temperature [2]. In hot weather, not replacing fluids fast enough during exercise can be much more serious and can lead to hyperthermia and cardiac impairment, otherwise known as heat stroke.
Reduced cognitive performance
Dehydration can also affect our brain function and power. Research suggests that even mild dehydration (water loss of 1-2%) is associated with disruptions to mood, poor concentration, reduced reaction times and memory loss [3]. The degree of cognitive impairment also appears to be directly related to the severity of dehydration. Increased water intake has been suggested to improve visual attentiveness and short-term memory [4], whilst fluid deprivation has been associated with fatigue, reduced alertness and low mood (including feeling less happy and calm) [5]. What’s more, studies suggest that dehydration may be a predisposing factor for confusion amongst those in long-term care (although research is commonly based on water intake as a proxy measure for dehydration rather than clinical assessments). Dehydrated adult brains also how signs of heightened activity when completing cognitive-based tasks compared to hydrated brains, suggesting our brains must work harder to complete mental tasks when dehydrated [6].
Disrupted GI function
Our fluid intake has a significant role to play in our gut health and digestive function. One of the most common and perhaps obvious gut-related effects of dehydration is constipation, characterised by small/hard stools, slow gut transit and difficulty opening bowels. It makes sense that increasing your fluid intake can be an effective treatment for constipation, but research suggests there is minimal effectiveness in those already hydrated [7].Disrupted kidney function
The kidneys play a vital role in regulating water balance and blood pressure as well as removing waste from the body. They require water for the filtration of waste to form urine. The minimum amount of water we need for this is known as the ‘obligate volume’ and this is dependent on several factors, including the amount of metabolic ‘material’ we need to excrete. Most of us will be aware that dehydration results in the production of highly concentrated urine. This can lead to the formation of mineral crystals which can impair kidney function and contribute to kidney problems like kidney stones.
Disrupted heart/cardiac function
Dehydration can also affect our cardiovascular system, including how well the lining of our blood vessels works in controlling our blood pressure, blood clotting and various other highly orchestrated mechanisms. A growing body of evidence suggests that this endothelial dysfunction can induce inflammation, impacting arterial stiffness and heart health in humans [8]. When dehydrated, our blood volume reduces, meaning the heart must work harder to compensate and maintain a healthy blood pressure. Less water in our blood means that the concentration of electrolytes (including sodium) increases, making blood thicker or more ‘viscous’.Headaches
Headaches can be caused by drinking either too much or too little water. Dehydration headaches are usually relieved after drinking enough water, usually between 30 minutes – 3 hrs. I always tell my clients to try having a glass of water before reaching for any pain medication for a headache as often it can be due to dehydration. The physiological mechanisms linking dehydration with headaches are not fully understood but are likely to involve intracranial dehydration and reduced plasma volume [2].
More rarely, headaches can be caused by overhydration which I explain in more detail below so please be careful and drink a reasonable amount of water. A 200ml glass is usually enough to restore hydration unless you are severely dehydrated in which case you may need an electrolyte solution and not just water.
Skin concerns
Water comprises 30% of our skin tissue. Since water contributes to the plumpness and elasticity of skin, it is not surprising that dehydration can affect our skin health. However, although adequate hydration can help us to improve skin thickness and density [9], unfortunately, drinking water has not been shown to prevent wrinkles and other signs of aging – despite what we may read in mainstream and social media!
Heightened stress response
Dehydration is a physiological stressor and has been shown to induce the body’s stress response. Elevated levels of the stress hormone cortisol have been observed among dehydrated athletes both pre and post-exercise when compared to adequately hydrated controls [10]. Whilst drinking more water is unlikely to be the answer to all of life’s problems, ensuring you are adequately hydrated could prevent placing additional stress on the body.
Effects of hyper-hydration
On the other end of the scale, hyper-hydration occurs when the body takes on too much water (water intake exceeds water loss). Under normal circumstances, the body can restore fluid balance by increasing the volume of water excreted in urine – and so, in most cases, drinking more water than we need simply results in more trips to the loo!
However, in some cases, hyper-hydration can lead to water toxicity which can have potentially fatal consequences. Nearly all known fatalities have been a result of water-drinking competitions or following intense exercise where extreme amounts of water were consumed, causing a dangerous loss of electrolytes.
Sodium is the electrolyte most affected by overhydration, and increased body water results in a decrease in sodium concentration (known medically as hyponatremia). Hyponatremia occurs when blood sodium concentration falls lower than 135 mmol/L [11] and can lead to an accumulation of water in cells of the brain, resulting in increased intracranial pressure. For this reason, initial symptoms of water toxicity can be vague (headache, disorientation, confusion, nausea, and vomiting) and easily misdiagnosed. Prolonged hyponatraemia can be serious, leading to coma and even death.
Why might we drink too much?
Medical reasons
It’s important to mention that excessive thirst and frequent urination are common symptoms of uncontrolled (or undiagnosed) diabetes. Elevated glucose levels in the blood (hyperglycaemia) force the kidneys to work harder to filter and remove the excess sugar. The kidneys require extra water to remove glucose which can lead to dehydration, resulting in increased thirst. Other medical explanations for increased thirst include sickle-cell anaemia, psychogenic polydipsia, and excessive bleeding [13]. Excessive thirst is a red flag and should always be investigated by your GP.Societal conditioning
In recent years, society seems to have exploded with messages that we all need to be drinking more water. A recent trend created by wellness influencers named the ‘Gallon water challenge’ encourages people to drink a whopping 4.5 litres daily (1 gallon) and promises benefits such as weight loss, suppressed appetite and flawless skin in return. This far exceeds the requirements of most people and is unnecessary at best, promoting needless trips to the bathroom. At worst, it is dangerous and can deplete the body’s electrolytes, as described earlier. If you feel you may fall into this category, consider checking in with your water intake and read on to find out how much you are likely to need.
Recommended fluid requirements
So how much water do we really need for optimal health?
There is rarely a ‘one size fits all’ message in terms of nutritional recommendations, and fluid is no exception. Despite numerous efforts to determine daily fluid requirements by scientists, there is still no universal consensus.
In the UK, NICE guidelines recommend aiming for 25-30ml per kilogram of body weight daily to maintain fluid balance [12]. Using this recommendation, a 60kg individual would require between 1500-1800ml fluid each day. Generic public health guidance from the NHS and the Eat Well Guide recommends aiming for 6-8 cups of fluids per day (around 1.5-2L), which is thought to meet the needs of most people. This does also include water equivalent beverages such as non-caffeinated herbal teas. Most guidelines also state that one glass of juice and one glass of milk can go towards your total fluids for the day noting that your body will have to put in a little extra work to digest juice and milk to make the water it needs available for hydration.
Whilst these guidelines may come as a surprise if you’ve been drinking under the assumption that you need litres upon litres of water per day for optimal health, there will always be exceptions to these guidelines. For example, if you participate in strenuous exercise, you will likely need more fluids to replace losses from sweat. The same is true if you live in warmer climates. If you drink a lot of coffee and other caffeinated drinks, you may lose more water through urination. You may also need to drink more if your diet is high in salty, spicy or sugary foods or low in hydrating foods such as fresh or cooked fruits and vegetables.
One of the best ways to judge your hydration status is to check the colour of your urine regularly. Typically, ‘healthy’ urine should be pale or straw coloured, whereas darker, strong-smelling urine is an indicator that you need to drink more. One of the reasons this is usually a better (albeit delayed) hydration marker than thirst is because our thirst can be influenced by many things. Hunger, mood, the composition of the foods we eat, social environment, injury, climate and even our sex hormones can affect our experience of thirst.
How much should we urinate?
A related topic (and a question I often get asked) is how frequently we should be visiting the bathroom. How often we urinate depends on several factors, but it is normal to need to go between four and ten times across a 24-hour period. On average, most people will need to urinate about seven times a day [14]. Whilst it may be perfectly normal to need to go to the loo more often, daily incidences of urinating more than eight times may signal a concern for too-frequent urination. Not only can this be an embarrassing issue, but it can also interrupt sleep and lead to feelings of dread and anxiety in situations where a toilet is not easily accessible. Frequent urination can simply be the result of drinking more than the body needs, so please check in with the advice and guidance in this blog. However, it could also be because of other issues that should be investigated by your GP.
A brief look at the link between our hormones and urinary frequency
Low oestrogen levels can increase your need to urinate. A decline in oestrogen is characteristic of the menopause, as well as other conditions such as functional hypothalamic amenorrhoea (FHA) which can be triggered by lifestyle factors including relative energy deficiency and other nutritional issues, excessive exercise and/or psychological stress.
Oestrogen receptors exist throughout the lower urinary tract and have been identified in the smooth muscle of the bladder, urethra (the tube carrying urine out of the body), pelvic floor and vagina [14].
Low oestrogen is a major cause of urogenital atrophy (the wasting away of muscle mass) and can lead to the shrinking and weakening of the bladder lining and urethra. This compromises the ability to control urinary functions and so may go some way to explaining symptoms such as increased frequency and urgency to urinate during the menopause, hypothalamic amenorrhoea and other periods of oestrogen deficiency. Shockingly, a study found that 70% of women identified the onset of urinary symptoms to occur simultaneously with their final menstrual period [15].
Other Risk Factors for Frequent Urination
A history of vaginal childbirth – childbirth can weaken the pelvic floor muscles that hold the bladder in place or lead to nerve damage
Pregnancy and other anatomical causes of intra-abdominal pressure
Pelvic floor dysfunction or having a weak pelvic floor
Stress/ anxiety induced urinary symptoms
Medical conditions including UTIs, bladder stones, diabetes, “overactive bladder”
Health trends and excessive fluid consumption
High intakes of caffeine and other diuretics
Alcohol consumption
Some medications and supplements
Is there a “best” type of water to drink?
Most of us live in areas where tap water is highly regulated for contaminants and is perfectly safe to drink on a day-to-day basis. Some people prefer the taste of mineral water, and I tend to agree. The natural minerals in this water help “top up” electrolytes and may help keep us better hydrated. It may be best to have mineral water in glass bottles (if you can access and afford it), as plastics and their hormone-disrupting chemicals are known to leach into the water and the environment. Of course, this is a very expensive option and not always the most convenient.
For those who want to filter their tap water for improved purity and taste, I recommend a filter like Phox, which adds back in essential minerals that most filters strip out. The water tastes more like bottled mineral water but at a much lower cost to your wallet and the environment. The glass jug also means there’s no risk of plastic contamination. There are others like this on the market, so have a look for one that suits you.
Another easy way to add minerals back into water is to add a few drops of an electrolyte solution like this one from Viridian. It’s the one I use after exercise when needed, to ensure I top up electrolytes which are so important in maintaining our adrenal and hormone health. If you click on this link you can use my code HDUNN10 for a 10% discount. This can be a healthier option than drinking a sports drink which may have unnecessary sugar or artificial additives but of course it’s better to drink whatever is available and rehydrate quickly than to risk dehydration.
Take-home messages:
The body works hard to ‘fine-tune’ fluid balance and keeps water levels within tight parameters.
Disruptions to water balance (under or over hydration) can have potentially serious health consequences.
Drinking more than your body needs is not usually dangerous but has little health benefit and leads to more frequent urination, which can be both embarrassing and frustrating.
There are no universally agreed recommendations for daily fluid intake, but most of us should meet our requirements by drinking 25-30ml/kg/day. The colour of our urine is a good indicator of hydration status.
Hormonal issues, including oestrogen deficiency due to the menopause or functional hypothalamic amenorrhoea (FHA), can be a culprit for urinary symptoms, including increased frequency and urgency.
Drinking water with electrolytes (natural minerals) is generally better than distilled or filtered tap water that may have been stripped of these essential nutrients
REFERENCES
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This article was researched with the help of Emily Boorman (BSc Human Nutrition), a Band 4 Dietetic Assistant Practitioner, Registered Associate Nutritionist (ANutr) and a wonderful intern at Holly Dunn Nutrition.
Photo by Engin Akyurt
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