We chatted to Dr Paul Anastasiades, PhD Neuroscientist and Senior Lecturer at the University of Bristol and co-founder/head of product development at Phizz, about the connection between your immune system and hydration and what we found out was nothing short of fascinating…

Over the Christmas period, I came down with not one but TWO colds. Having managed to avoid colds all year – to get two at Christmas felt particularly unfair. Especially as I was hosting for 13 people. I couldn’t work out why; I had been taking my supplements, eating well (bar the addition of the odd mince pie) and getting lots of fresh air. It wasn’t until I spoke to a friend who is a Nutritional Therapist that mentioned that it could be my hydration levels that were the problem. That was when I realised – due to the incredible full-on-ness of the mad holiday season – I barely managed to drink a glass of water until about 3pm most days – it was actually a fairly shocking realisation. Drink more water is number one on my new years resolution list – I even bought a new water bottle to make the whole experience a tad more fun (if drinking water can ever be fun).I have worked in wellness for over 13 years now and I had never known that our immune systems were linked to hydration. So I decided to see if there was research to back the whole theory up – and there was loads of it! What’s more – it seems that a lot of the time water isn’t actually what our bodies need – we need to be fueling our cells with electrolytes as well as water… enter Dr Paul Anastasiades,  PhD Neuroscientist, and Co-Founder of leading electrolyte brand, Phizz, who knows only too well the impact that hydration has on the immune system. Dr Anastasiades explained that “one of our first lines of defence against infection are the mucous membranes that cover the surfaces of our mouth, nose and lungs. Normally these surfaces act to trap invading viruses, quickly moving them to our stomach to be killed by stomach acid. When we become dehydrated these membranes dry out, meaning that the invading nasties don’t get trafficked away from the site of potential infection as effectively, giving the virus more time to invade the body and cause illness.”. Through research it also seems that hydration also supports lymphatic circulation, which depends on fluid balance to move immune cells throughout the body where they’re needed. Without enough water, lymph flow slows, potentially delaying immune responses.

Water makes up about 60% of the human body and is involved in almost every vital process our cells perform. When hydration falters, so do many of the mechanisms that keep us healthy, including those tied directly to the immune system. A 2024 review in the Journal of the Association of Physicians of India highlights how even mild dehydration can interfere with immune function at both cellular and systemic levels, affecting immune cell communication, reducing the effectiveness of pathogen response mechanisms, and impairing recovery from illness.

A review published in the Journal of the Association of Physicians of India explains that even mild dehydration can disrupt immune function at cellular and molecular levels, including cell communication, migration, and pathogen response, because immune processes often rely on water-dependent mechanisms and fluid balance.

Breaking Down The Immune System:

GUT

A 2024 study published on PubMed found that water restriction in animal models impaired immune homeostasis in the gut, decreased immune cell numbers (especially T helper cells), and reduced the ability to eliminate enteric pathogens, showing that underhydration compromised local immune defense mechanisms.

HORMONE
Research involving exercise and hydration shows that fluid restriction affects hormone levels like cortisol, which in turn modulates immune response – especially the production of certain cytokines involved in inflammation and pathogen defense. As well as this Dr Anastasiades explains that “one of the hormones that is secreted when we become dehydrated is the stress hormone cortisol. Cortisol is released when your body encounters either physiological (changes in thirst, hunger, temperature, sleep) or psychological (threats, interpersonal, financial) stress. Importantly, being chronically dehydrated can make you much more prone to respond to stressful situations in your daily life with higher cortisol levels and a stronger emotional response.” Which leads us onto another big thing that affects the immune system and that is stress itself.

STRESS
A clinical study comparing people with low vs high habitual water intake found that lower hydration was associated with higher oxidative stress and negative shifts in immune cell responses after exercise, suggesting that chronic low water intake can weaken key aspects of immune resilience. Consistent hydration supports the body’s oxidative balance and immune cell activity, particularly under stress.

Dr Paul Anastasiades Shares His Gold-Standard Hydration Habits:

Top tip for increasing hydration

“Your body needs around 2 litres of water a day,  although this will vary a lot from person to person based on activity levels and environment. Aim to drink smaller amounts of water regularly throughout the day (this can help your body absorb it more efficiently) and ensure you don’t wait to get thirsty before you act to rehydrate. Adding electrolytes (particularly sodium) and also some glucose can enhance water absorption, hydrating you more efficiently.”

Common hydration mistakes

“Hydration isn’t something super complex that is hard to get right. Most people manage fine. Busy work schedules (lots of back to back meetings without a break) can make it hard to drink regularly so keep a water bottle with you at all times. Drinking lots of soft drinks full of sugar is not ideal.  One place where people often misstep is on aeroplanes. Plane cabins are very dry (dryer than the Sahara) and being stuck in that environment for a long period of time can really dehydrate your body.”

Best time to take hydration tablets such as Phizz

“Mornings are good as you may feel a bit dehydrated already after having been without fluids overnight. However, the best time is what works for you and your daily schedule.”

How to support your immune system?

“I typically advocate for simple solutions. Eat well, stay hydrated, and get lots of sleep and exercise. In the winter you may want to consider supplements that contain at least 10µg of vitamin D such as Phizz Daily Immune+, which delivers proactive support every day, with vitamins D, C, B6, A and E, plus iron, zinc and selenium to keep your defences ready.  It also contains powerful antioxidant molecules to combat free radicals, helping reduce cell damage and providing an extra layer of immune support.”

Phizz Daily Immune+ is available from Tesco, Waitrose, Ocado and Amazon.  It is also available at Phizz.co