It’s the system that quietly and consistently underpins almost every function that keeps us alive and thriving: hydration.
Our bodies are more than 50% water, with H2O making up 75% of our brains, and 90% of our blood plasma.
Our cells rely on water to maintain their structure, as well as to shuttle nutrients around and remove waste. When we talk about “optimising” our health in midlife and beyond, hydration really is key.
What dehydration actually does to your body
When we think about dehydration, many of us may picture heatstroke, fainting and possibly even desert scenes.
In reality, the physiological effects begin much earlier.
“The physiological impact of dehydration is generally on a dose-response basis,” explains Dr Lewis James, a reader in human nutrition at Loughborough University. “These effects start to appear when dehydration is equivalent to 1–2% of body mass.”
For a 70kg woman, this equates to less than 1kg of fluid. Here, blood volume decreases slightly, the heart works a little harder and temperature regulation becomes less efficient. While we won’t faint, we may feel… off.
What the science shows
Research published in The Journal of Nutrition found that women who were mildly dehydrated (around 1.3% body mass loss) experienced:
- Increased fatigue
- More frequent headaches
- Reduced concentration
- Greater perception of task difficulty
This becomes more relevant as we age, too.
“In older adults, thirst may not be an entirely reliable signal,” says Lewis.
Professor Sarah Berry, Professor of Nutritional Sciences at King’s College London, agrees: “While the body regulates water remarkably well, these mechanisms can become slightly less reliable as we get older,” she says.
Add in midlife realities such as hot flushes, disrupted sleep and an evening glass (or two) of wine, and it’s little surprise that mild, chronic under-hydration can creep in.
And it goes further than ‘just’ feeling a little tired every now and again. Research suggests that long-term hydration habits may track with cardiovascular and metabolic health.
A 2023 study examined serum sodium levels (a marker influenced in part by long-term hydration habits) in more than 11,000 adults over three decades.
Individuals with sodium levels in the higher end of the normal range were more likely to show markers of accelerated biological ageing and had a higher risk of chronic disease.
The theory is that when fluid intake is consistently low, the body increases vasopressin (a hormone designed to conserve water). Persistently elevated vasopressin has been associated with a greater likelihood of heart issues, metabolic dysfunction and kidney strain, particularly in people already at higher risk.
There’s also emerging evidence that dehydration can gently increase some of the body’s stress and inflammation signals. In the short term, that’s simply adaptation, but if those signals are activated repeatedly over years, they may contribute to low-level strain on blood vessels, kidneys and metabolic balance – the very systems we’re trying to protect.
So how much do we actually need?
There’s no ‘one size fits all’ when it comes to hydration. However, the European Food Safety Authority suggests around 2 litres of total water per day for women (including water from food). In practice, many adults will need closer to 2-3 litres of fluids daily depending on body size, climate and activity.
Lewis suggests something refreshingly simple: aim for roughly 2.5-3 litres per day, spread evenly throughout the day.
When thirst signals soften with age, Sarah recommends keeping an eye on the colour of your urine. “It should be a light straw colour,” she says. “If it’s darker, that’s a good sign you need a drink.”
Other signs such as headaches, dips in concentration, dry mouth and constipation vary between individuals. But if you’re feeling flat, hydration is an easy place to start.
Optimising hydration – without overcomplicating it
Electrolytes, hydrogen water and hydration powders are becoming increasingly popular – but how helpful are these?
“Electrolytes, particularly sodium and chloride, influence fluid retention,” says Lewis.
After intense exercise, in hot weather, during travel, periods of stress, or if you’re prone to feeling light-headed or fatigued, a well-formulated electrolyte supplement can be helpful – particularly for supporting energy and maintaining fluid balance. Many people also find they simply feel better when adding a small amount to their water, especially first thing in the morning.
Hydrogen water is another area attracting interest. Early research suggests potential antioxidant and anti-inflammatory effects, although larger and longer-term human studies are still needed. The science is promising, particularly in the context of healthy ageing and cellular resilience.
And what about tap water?
Google ‘tap water’ and things can escalate quickly – microplastics, traces of hormones, antibiotics and heavy metals. It’s enough to make anyone look at their kitchen tap a little suspiciously. But what’s the real story?
In the UK, drinking water is tightly regulated, and overall standards are considered high. Current evidence suggests that levels of most contaminants in treated drinking water are well below those thought to pose a risk to human health.
That said, scientists are increasingly detecting tiny amounts of substances such as microplastics and endocrine-disrupting compounds in water systems around the world. The World Health Organization has reviewed the available evidence and concluded that, at the levels currently found in drinking water, microplastics do not appear to pose a clear health risk. However, research in this area is still evolving.
“It’s a bit of a minefield,” says Sarah. “If you’re concerned, certain water filters can reduce some contaminants, but bottled water isn’t necessarily the cleaner solution, particularly when plastic packaging may introduce its own exposures.”
For many people, this is where a simple household water filter can offer reassurance. Filtering won’t solve every issue, but it can help reduce certain impurities and improve taste.
In a nutshell
Mild, persistent underhydration may quietly increase physiological strain over time – on the cardiovascular system, metabolic regulation and cognitive performance.
This can make a big difference in midlife when small changes accumulate.
Focus on:
- Roughly 2–3 litres of fluids daily (adjusted for you)
- A steady rhythm throughout the day
- Light straw-coloured urine as your compass
- Cutting down on excess alcohol
- A little more intention as thirst signals soften
It is not glamorous advice, but it is biologically sound and in the long game of ageing well, foundations matter far more than fads.
