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Most people understand that regularly drinking enough water is important for overall health, but the benefits of staying optimally hydrated specifically for supporting immune function are perhaps less well known.

On average, the human body is about 60% water; this figure varies with age (total body water content reduces as we get older) and body composition (the higher your lean tissue, the higher your total body water content will be), and some parts of the body contain more water than others (brain, heart, lungs, liver and kidneys typically contain a lot of water). The clear elixir of life is absolutely vital for every aspect of health, and we can’t survive for long without it. Water is critical for the immune system to function optimally too.

Here we look at how staying optimally hydrated may impact immune function and share 10 top tips to help you stay well hydrated every day.

How optimal hydration may support immune health

✔ Immune communication & biochemical pathways
Optimal hydration may help to support communication and biochemical pathways in the immune system.

✔ Supports blood volume
Your immune system relies on your blood stream to transport fluid, nutrients and important communication signals to organs. Since blood plasm is about 90% water, hydration is necessary to support this.

✔ Lymphatic system
Being well hydrated is also important for a well-functioning lymphatic system which works closely with the immune system. The lymphatic system relies heavily on a clear and colourless fluid called lymph which is made up of about 90% water. Less body water content may mean less lymph production. A well-functioning lymphatic system helps to remove toxins, waste, debris, abnormal cells and pathogens from the system; it also helps to transport infection-fighting white blood cells throughout the body.

✔ Histamine balance
There is evidence that histamine release may be enhanced under extreme conditions such as dehydration or hypoglycaemia or by a variety of stressors.1 Histamine is a central mediator released from mast cells and involved in many different body processes. Perhaps best known is histamine’s role in familiar allergic symptoms such as mucus production, itching, wheezing, rashes and hives. Hence why ‘anti-histamines’ are the over the counter medications typically used to reduce allergic symptoms in problems such as hayfever.

Studies and Reviews

✔ In a 2013 study published in Luminescence, researchers investigated the effects of dehydration on immune functions in 25 university judoists after a judo practice session. Subjects were divided into two groups according to their level of dehydration after practice (mild dehydration and severe dehydration). Results suggested that dehydration resulted in immunosuppression, including decreased neutrophil (an important type of tissue-healing and infection-fighting white blood cell) function.2

✔ In a 2012 study published in Applied Physiology, Nutrition & Metabolism, researchers investigated the effect of exercise-induced dehydration and subsequent overnight fluid restriction on saliva antimicrobial proteins (AMPs) important for host defence (secretory IgA (SIgA), α-amylase, and lysozyme). The researchers concluded that modest dehydration decreased salivary flow rate (SFR), α-amylase, and lysozyme secretion rates. However, they also commented that whether the observed magnitude of decrease in saliva AMPs during dehydration compromises host defence remains to be shown.3

✔ In a 2019 review, researchers evaluated the effects of dehydration on several kinds of allergy responses and exercise-induced asthma especially during endurance exercise. They found that exercise-induced dehydration reduces airway surface hydration, resulting in increased bronchoconstriction. This is a response to exercise in exercise-induced asthma individuals and asthma patients.4

10 Top tips to help you stay optimally hydrated every day

1. Keep caffeinated drinks in check
Drinking too much tea and coffee may have a negative impact on your hydration status. This is because they contain caffeine which has well-known diuretic activity. In simple terms, ‘diuretic’ means it increases water excretion from the body. Research has demonstrated diuretic effects of caffeine, however there is ongoing debate over the magnitude of this and whether it’s something we need to be concerned about. It seems that the diuretic effects of caffeine are at their greatest when the subject is young and not used to drinking caffeine.5 Our takeaway message is that you don’t need to avoid tea and coffee completely but it’s important to keep your overall intake in check and that you aren’t relying on caffeinated drinks as your only source of hydration.

2. Invest in a glass or metal water bottle
Whatever your thoughts on caffeinated drinks there’s no disputing that the best way to hydrate is with plain, filtered water. You’ll find it easier to drink enough if you always have it readily available. Invest in a glass or metal (not plastic) water bottle and get into the habit of taking it with you wherever you go.

3. Reduce alcohol intake
There’s no denying the diuretic effects of alcohol and that drinking too much will most certainly dehydrate you. Every alcoholic drink causes a net fluid loss, and when one drink turns into a few more, the dehydrating effects can soon stack up. If you want to stay optimally hydrated, you need to keep alcoholic drinks to a minimum and make sure you drink plenty of water too – this won’t negate the dehydrating effects completely but will at least help to minimise them.

4. Cut back on processed, salty foods
Eating too many salty foods can have a dehydrating effect on the body since the body will try to eliminate excess sodium by increasing the frequency of urination. We do need sodium in our diets but processed, convenience foods often contain way more than we need.

5. Replace water lost through exercise / heat
Some circumstances will increase your body’s needs for water; such as when the temperature increases or during exercise. It’s therefore important to be mindful of increasing your normal daily fluid intake when your body’s demands increase. If you’re exercising for prolonged periods and especially in hot, humid environments, you also need to be mindful of replacing electrolytes lost through sweat.

6. Choose powdered supplements
Even simple strategies such as choosing powdered supplements that need to be heavily diluted can help to support overall fluid intake. Powdered magnesium supplements with added co-factors to support muscle function and energy production may be especially beneficial for regular exercisers.

7. Don’t wait till you’re thirsty
Most people wait until the thirst reflex tells them to reach for some liquid nourishment, at which point they’re already pretty dehydrated. The best way to avoid dehydration is to keep drinking regularly throughout the day, and as a general rule, you shouldn’t be regularly reaching the point where you’re thirsty and gasping for a drink.

8. Aim for 8 glasses daily
The total amount of water needed each day varies from one individual to another and this is another area that continues to be heavily debated, you therefore need to listen to your own body to determine what’s right for you. If you aim for around 8 glasses of water daily you’re likely on the right track.

9. Add herbal teas into your daily mix
Whilst the best way to stay hydrated is to regularly drink pure, filtered water, including some variation of fluids into the day may encourage you to drink a bit more. Caffeine-free herbal teas can be a great way to up your overall fluid intake. Try peppermint, chamomile, nettle and lemon & ginger.

10. Consider extra vitamin C & bioflavonoids
If you are struggling with seasonal sensitivities, in addition to being mindful of your water intake, nutrients such as vitamin C with added bioflavonoids may help to support overall histamine balance. Vitamin C and bioflavonoids are also important for overall immune system function. A powdered vitamin C supplement may deliver added benefits by gently helping to increase overall fluid intake too.

Read more about hydration in our article 6 Delicious Ways to Stay Hydrated This Summer.

1. Brown RE, Stevens DR et al. The physiology of brain histamine. Prog Neurobiol. 2001 Apr; 63 (6): 637-72
2. Chishaki T, Umeda T et al. Effects of dehydration on immune functions after a judo practice session. Luminescence. Mar – Apr 2013; 28(2): 114-20
3. Fortes MB, Diment BC et al. Dehydration decreases saliva antimicrobial proteins important for mucosal immunity. Appl Physiol Nutr Metab. 2012 Oct; 37(5): 850-9
4. Kim KB & Kwak YS. Dehydration affects exercise-induced asthma and anaphylaxis. J Exerc Rehabil. 2019 Oct; 15(5): 647-650
5. Marx B, Scuvee E et al. Mechanisms of caffeine-induced diuresis. Med Sci (Paris). 2016 May; 32(5): 485-90

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Nutri Advanced has a thorough research process and for any references included, each source is scrutinised beforehand. We aim to use the highest value source where possible, referencing peer-reviewed journals and official guidelines in the first instance before alternatives. You can learn more about how we ensure our content is accurate at time of publication on our editorial policy.