The lowdown on hydration and type 2 diabetes

When we talk about type 2 diabetes, we often focus on dietary factors (such as weight loss) for disease management, the effect of food intake on blood sugar, or the interplay of glucose and insulin levels in the body. But what about water?
Annabel Nicholson
min read
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Quick summary

  • It's important to drink enough whether or not you have type 2 diabetes, but staying hydrated is especially important for those with a diagnosis.
  • Know the signs of dehydration and keep water on hand for moments you might run low.
  • Mix up your water drinks with healthy flavourings to make them more interesting.

Regardless of the time of year, staying hydrated is important for everyone... and this particularly true for people with diabetes. You may be aware of, or have even experienced, two common symptoms of type 2 diabetes – increased urination and thirst. What causes these symptoms? Are people with diabetes more at risk of dehydration? How much water should you drink to stay hydrated? Read on to find answers to all these questions as we bring you the full lowdown on hydration and type 2 diabetes.

Why is water so important?

The human body is approximately 60% water. It’s the oil to our machine and is vital to our survival. Hydration is crucial for digestion, for our heart and circulation, for temperature control, and for our brain. It’s undoubtedly the most essential component of the human body, and yet we’re pretty terrible at keeping our fluid levels regularly topped up. We all need to stay hydrated, but for people with diabetes it is very important.

Water and diabetes

If you've been diagnosed with type 2 diabetes, it's the combination of fat deposits around the pancreas and insulin resistance that lead to the hallmark of type 2 diabetes – hyperglycaemia, a fancy word for a state of elevated blood sugar. A dry mouth and dry eyes are telltale signs of a body being hyperglycaemic, not to mention an unquenchable thirst and increased need to urinate.

Why is this happening?

When blood glucose levels remain high for an extended period of time, the kidneys work hard to filter the excess glucose from the blood and remove it from the body via urine. At the same time, water is drawn from cells into the bloodstream in an attempt to dilute the increased levels of glucose. With the kidneys ramping up a gear and having to process more fluid, they produce more urine. The brain then tells you to drink more to replace the fluid that you’ve lost, making you feel thirsty.[1]

Dehydration and diabetes

It’s essential for everyone to keep well hydrated, but for those with diabetes, it’s even more vital. Diabetes leaves you more susceptible to dehydration and, if ignored, can be very dangerous.

As discussed above, a spike in blood glucose levels causes water to enter the bloodstream to dilute the concentration of glucose. If someone with diabetes is already dehydrated, the body will find water reserves from elsewhere such as saliva and tears, causing that telltale dry mouth and eyes mentioned earlier.[2]

A lack of water also means less urine is produced, so the body isn’t able to expel excess blood glucose via urination. This then loops back to a rapid rise in blood glucose levels, resulting in further dehydration as the body continues to look for water to dilute the blood.

Drinking water rehydrates the blood, lowering the concentration of glucose in the bloodstream and helping the kidneys produce more urine to expel the excess glucose.

What about dehydration from heat and exercise?

In warm temperatures or during exercise, the body cools itself down by sweating. For a person with diabetes, the water lost through sweat means that proportionally there is a high level of glucose in the blood compared to the remaining volume. 

If you have diabetes or even prediabetes, it’s important to be extra-vigilant in the warmer months and when you’re active. If you monitor your blood glucose levels, do so before, during, and after exercise. Also, be sure to drink plenty of water, and try to avoid the hottest part of the day.

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What are the signs of dehydration?

It’s worth familiarising yourself with the signs of dehydration. According to the NHS[3], these include:

  • Feeling thirsty
  • Dark yellow or strong-smelling urine
  • Feeling dizzy or lightheaded
  • Feeling tired
  • A dry mouth, lips and eyes
  • Urinating small amounts and fewer than four times a day

If ignored, severe dehydration can be fatal. If you or someone you care for exhibits any of the following symptoms of severe dehydration, seek medical help:

  • Low blood pressure
  • Sunken eyes
  • A weak pulse and/or rapid heartbeat
  • Confusion
  • Lethargy

Sometimes it's difficult to know the difference between being dehydrated and having elevated blood glucose levels, as both will make you thirsty. Check the colour of your urine to determine your hydration - a straw colour suggests you are properly hydrated.[4] The darker the colour, the less hydrated you are. If you’re concerned, contact a health professional and slowly drink fluids in the meantime. If you have another condition and have been advised to reduce your fluid intake, be sure to talk to your medical team for advice about how to balance these two (often opposing!) pieces of guidance. 

How much water should we drink?

You’re probably already familiar with the ‘standard’ recommendation of drinking around eight glasses of water a day. Allegedly, this recommendation can be traced back to a study published in 1921.[5] The author measured his own urine and sweat output and calculated that he lost about 3% of his body weight in water a day. This turns out to equal approximately eight glasses, meaning that, for a very long time, human water requirements were potentially based on one person’s urine and sweat measurements…!

Fast forward 100 years, and we now have extensive evidence that not drinking enough water may be associated with a number of medical problems.

So, how much should we be drinking?

General advice in the UK still stands at 6-8 glasses a day, with more required in hot weather and when exercising.[6]

Even if you don’t feel thirsty, a few sips of water every hour will help you stay hydrated.

That being said, rather than drinking towards a fixed goal each day, consider getting into the habit of having water nearby at all times. Even if you don’t feel thirsty, a few sips of water every hour will help you stay hydrated. The thirst reflex isn’t always perfect, especially for people with diabetes, so it’s better to proactively drink some water than risk even just mild dehydration.

Thirst quenchers

Tea, coffee, milk, fruit juices, and smoothies all technically count towards daily fluid intake, but since tea & coffee come with caffeine and fruit juices/smoothies are loaded with sugar, water really is the best option to quench your thirst.[7] Endless glasses of plain water can get a bit monotonous, so mix it up to keep things interesting: 

Make your own flavoured water
Pep up your beverage by adding a squeeze lemon, lime, strawberries, mint, or cucumber to a glass of iced water. There are loads of flavour combinations to explore, so have fun experimenting!

Create your own fizz
Mix sparkling water with a splash of squash, cordial, or one of your new-found flavour combinations to make your water feel a bit more celebratory.

Get creative with ice cubes
Freeze chunks of watermelon or grapes to use as colourful, tasty ice cubes.

Try a herbal infusion
Refreshing, caffeine-free, and with plenty of choice, herbal teas are a great way to up your fluids. Make your own mint tea by adding fresh mint leaves to boiling water.

Avoid fruit juice, or dilute it to start with
Fruit juice is a bit of a villain in disguise (particularly for those with diabetes), and can hamper your best efforts to cut down on sugar. It contains all of the sugar and far less of the nutrients present in whole fruits (so a lot of the good done by the hydration from a glass of juice is undone by the sugar spike associated with it). So while a glass of fruit juice may technically count towards your five a day, our official guidance would be to ditch the juice in favour of a whole piece of fruit and some water. 

If you’re not ready to give up juice entirely, gradually add water (or sparkling water!) to your juice to get used to less sweetness. 

Reach for milk after exercise
If you’re looking for something besides water for after a workout, milk is not only hydrating but also a good source of calcium, protein, and carbohydrates. 

Eat water-rich foods
We also obtain fluid from food, especially fruit and veg. Cucumber, courgette, watermelon, and grapefruit are all foods with a high water content.

It’s easy to forget to drink throughout the day (guilty!), so set yourself up for success. Make up a jug of flavoured water and leave it on your table or desk for the day. You’ll be more likely to drink it and, as the day goes on, the flavours will intensify. If you’re out and about, try to get into the habit of taking a reusable water bottle out with you. Cafes and restaurants are often happy to provide free tap water refills, so you don’t have to worry about being caught out.

Water intake is an important element of type 2 diabetes management, but don’t panic - there are plenty of creative ways to help up your fluid intake and make hydrating part of your lifestyle. Happy hydrating!


[1] Water and diabetes. Retrieved 1 July 2021. Accessible here.

[2] Dehydration and diabetes. Retrieved 1 July 2021. Accessible here.

[3] Dehydration. NHS. Retrieved 1 July 2021. Accessible here.

[4] McKenzie, A.L., Muñoz., C.X., Armstrong, L.E. (2015). Accuracy of Urine Color to Detect Equal to or Greater Than 2% Body Mass Loss in Men. J Athl Train 50(12): 1306-1309.

 Accessible here.

[5] Greger, M., Stone, G. (2016). How not to die. Pan Macmillan, London.

[6] The Eatwell Guide. NHS. Retrieved 1 July 2021. Accessible here.

[7] The importance of hydration. British Dietetic Association. Retrieved 1 July 2021. Accessible here.

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