Mild dehydration affects multiple bodily systems, not just thirst, and most people spend the majority of their lives in this state without registering any desire to drink, according to Dr Dore Jalaei, a health consultant at the Reborne Longevity Clinic in London. The consequences, she warns, extend well beyond simple discomfort, impairing cognitive performance, elevating heart rate and placing strain on renal function, while accumulating over the years into accelerated biological ageing at the cellular level.
The hidden toll of mild dehydration
Dr Jalaei told GB News that one of the most pervasive yet unrecognised issues in modern health is persistent low-level dehydration. “Most people spend most of their lives mildly dehydrated without registering thirst,” she said. “Even mild dehydration impairs cognitive performance, elevates heart rate and places strain on renal function. Over the years, inadequate hydration is increasingly linked to accelerated biological ageing at the cellular level.” The damage, she stressed, accumulates silently and often goes unnoticed until significant harm has occurred.
In the UK, dehydration is a common but frequently poorly diagnosed condition among older adults, due to physiological changes that come with ageing, including a reduced sensation of thirst and less efficient kidneys. Symptoms such as fatigue, constipation and headaches are often attributed to other factors in older individuals. Cognitive and physical problems can arise with even a 1 per cent loss of body water. Dehydration in older adults can lead to urinary tract infections, kidney stones, constipation, delirium, confusion and an increased risk of falls, and can exacerbate chronic conditions such as diabetes and heart disease. Globally, approximately one-third of non-hospitalised older people are estimated to be dehydrated.
Proper hydration is essential for joint lubrication, muscle function and nutrient transport. Health guidance recommends at least eight to ten glasses of water per day, with more needed when physically active or in hot climates. Caffeinated and alcoholic beverages should be limited as they can contribute to dehydration. Around 20 per cent of water intake comes from food, with the remaining 80 per cent from drinks. Hydrating foods such as fruits and soups, along with non-alcoholic fluids, contribute to overall intake.
The overlooked importance of skeletal muscle
The next most overlooked factor compromising longevity, according to Dr Jalaei, involves the body’s muscular tissue. “Skeletal muscle is not just aesthetic,” she stated. “It is the primary site of glucose disposal, a major regulator of metabolic rate and a predictor of all-cause mortality. Grip strength alone has been shown to predict cardiovascular outcomes with remarkable accuracy. Most people do not begin serious resistance training until the decline is already underway.”
Muscle mass is directly linked to metabolism, burning more calories at rest, and strong muscles are crucial for maintaining balance, flexibility and strength, reducing the risk of falls, a leading cause of death and disability in older adults. Muscle strength is a significant predictor of coronary heart disease and stroke risk later in life. Low muscle strength is linked to cognitive decline and may reduce dementia risk. Resistance training, which builds muscle, also strengthens bones, reducing osteoporosis risk. Muscle also supports the immune system and acts as an anti-inflammatory organ.
Muscle mass declines with age, starting as early as the thirties, at a rate of 3 to 8 per cent per decade, a condition known as sarcopenia. By age 80, approximately 30 per cent of peak muscle mass can be lost, with the decline exacerbated by inactivity and poor nutrition. In the UK, a sedentary lifestyle is a stark contrast to ancestral needs, and muscle strength is a strong predictor of mortality, according to research published in the British Medical Journal. Maintaining muscle mass through diet and resistance training is vital for long-term health, mobility and independence.
Resistance training, focusing on exercises that target major muscle groups such as squats, lunges and deadlifts, is the most effective form of exercise for building strength and lean muscle mass, with intensity gradually increased. Adequate protein intake is crucial for muscle health, with guidance recommending 20 to 30 grams of protein per meal from sources such as chicken, fish, beans, lentils, eggs or plant-based powders. Dr Dorsa Jalaei, also associated with the Reborne Longevity Clinic, recommends 30 grams of protein at breakfast to stabilise blood sugar and support metabolism.
Ultra-processed foods and biological ageing
These minor daily decisions, Dr Jalaei cautioned, compound over decades into quantifiable biological deterioration, including the consumption of ultra-processed foods, another significant threat to longevity. “The NOVA classification of ultra-processed foods has reshaped nutritional epidemiology,” she said. “These foods are designed to be hyperpalatable, calorically dense, and nutritionally hollow. Beyond caloric considerations, additives, emulsifiers, and artificial sweeteners in these products appear to directly disrupt gut microbiome composition and drive low-grade systemic inflammation.”
Ultra-processed foods are linked to higher risks of obesity, type 2 diabetes, cardiovascular disease, poor mental health and various cancers. Regular or high consumption is associated with poor dietary patterns and an increased risk of early death, with one study suggesting a 10 per cent higher risk. They can accelerate biological ageing at a molecular level, potentially shortening telomeres; one study found telomeres equivalent to 4.5 extra years of ageing in high consumers. They also directly contribute to low-grade inflammation, a key factor in heart disease and other chronic illnesses, and disrupt metabolism by causing glucose spikes and insulin surges. Emerging research suggests they may affect gut health by interacting with the gut microbiome.
In the UK, ultra-processed foods provide over half of the calories in the average diet. Evidence suggests higher consumption is strongly associated with a higher risk of obesity and abdominal obesity in the adult population. The Scientific Advisory Committee on Nutrition (SACN) considers the association between higher consumption of these foods and adverse health outcomes concerning, though limitations in evidence mean it remains unclear whether the processing itself or the typical nutritional profile high in fat, sugar and salt is the main driver. The Eatwell Guide already indicates that many ultra-processed foods, such as crisps, biscuits, cakes and confectionery, are not part of a healthy diet.
The NOVA classification system has faced criticism for its broad categories, potentially leading to negative perceptions of some nutrient-dense, affordable foods. Some research suggests that specific categories such as processed meats and sugar-sweetened beverages are the primary drivers of negative health risks, rather than all ultra-processed foods being equally detrimental. Guidance recommends focusing on whole, minimally processed foods: fruits, vegetables, whole grains, legumes, nuts and lean proteins, and reading ingredient lists to be mindful of added sugars, saturated fats and excessive sodium.
Heatwaves accelerate biological ageing
Research published in Nature Climate Change last year revealed that repeated heatwave exposure accelerates the ageing process, with harmful effects comparable to smoking and alcohol consumption. Extreme temperatures strain the cardiovascular and renal systems, while cumulative cellular damage, including DNA deterioration and chronic inflammation, may independently hasten biological decline. The study found that two years of heatwave exposure accelerated biological ageing by an average of eight to 12 days. Biological age rose by about nine days for every four additional heatwave days over that period. Manual workers, who spend more time outdoors, were significantly affected, with their biological age accelerating by 33 days. Rural residents and those without air conditioning also showed greater impacts.
Prolonged heat exposure can modify gene behaviour, speeding up ageing at the molecular level. People in extremely hot areas appeared biologically about 14 months older, epigenetically, than those in cooler regions, and this accelerated biological ageing is associated with a higher risk for disease and mortality. In the UK, warming temperatures and more frequent heatwaves are being recorded. Temperatures above 25°C are linked to increased risk of heat-related deaths and hospital admissions, primarily due to exacerbation of cardiovascular and respiratory diseases. Vulnerable groups, including older people, pregnant women and children, are particularly affected. Heatwaves can exacerbate air pollution, further impacting respiratory and cardiovascular health, and have been associated with negative mental health effects, including increased aggression, irritability and a higher risk of suicide. In 2024, there were 1,311 heat-associated deaths in England, with significant deaths occurring even during yellow Heat-Health Alerts. Guidance for coping with heat includes keeping out of the sun between 11am and 3pm, wearing light clothing and sunscreen, cooling down with cold food and drinks, avoiding alcohol and hot drinks, keeping living spaces cool by closing windows during the day and opening them at night, and staying hydrated by drinking plenty of water.