Scientists have pinpointed the most exhausting decade of life – and it’s bad news for anyone approaching their 40th birthday.
According to Professor Michelle Spear, an anatomist from the University of Bristol, our 40s are the most tiring years of our entire lives.
This isn’t just because we are getting older, but rather because small biological changes converge at the same time.
To make matters worse, these changes coincide with a period in which the demands of life, work, and parenting often reach their peak.
Professor Spear told the Daily Mail that midlife fatigue is best understood as a ‘mismatch between biology and demand’.
She says: ‘Our bodies are still perfectly capable of producing energy, but they do so under different conditions than in earlier adulthood, while the demands placed on that energy often peak.’
However, the good news is that these biological imbalances that sap our energy are only temporary.
In fact, many people may even experience a second wind as they get older, according to the expert.
Scientists say that our 40s are the most exhausting age, as multiple biological changes coincide with the period of highest demand on our bodies and brains (stock image)
Looking back on your 20s, it might have felt like everything was just a little bit easier for your body.
You could go to sleep later, stay out longer, exercise more sporadically, and still stay in relatively good shape.
Surprisingly, the science of ageing suggests that this feeling is actually correct.
‘In our 20s, the body is biologically very forgiving,’ explains Professor Spear.
‘Muscle repair is faster, inflammatory responses are shorter–lived, and energy production at a cellular level is both efficient and plentiful.’
The parts of our cells responsible for making energy, known as mitochondria, provide us with more energy with less waste and fewer inflammatory byproducts.
Professor Spear says: ‘When you have more available energy, everything costs less, so poor sleep, a late night, or intense exercise simply has fewer consequences.’
However, by the time we reach our 40s, small shifts begin to destabilise this finely tuned system.
From the late 30s onwards, muscle mass starts to decline naturally unless it is maintained with regular strength training.
When we have less muscle, small everyday movements start to cost more energy than they did in our 20s.
While the mitochondria still produce energy, they do so less efficiently – leaving us with less energy and more waste.
This makes recovery more biologically expensive, meaning a late night or period of stress that wouldn’t have been an issue in our 20s starts to take more of a toll.
At the same time, one of the biggest changes that occurs during our 40s is that sleep starts to worsen.
During our 20s, sleep is deeper and more efficient, so that even shorter periods of rest lead to physical and mental restoration.
When we get older, the systems that generate and protect this deep sleep become less stable.
Professor Spear says: ‘Hormonal changes, particularly fluctuating oestrogen and progesterone for women during perimenopause, directly affect the brain regions that regulate sleep depth and body temperature.
Previous studies have shown that our brains reach ‘adulthood’ in our 40s (pictured). However, this also comes alongside changes that lead to less efficient sleep
‘This makes it harder to stay in slow–wave, restorative sleep.’
Meanwhile, the body’s stress response becomes more active with age, making it more likely that cortisol will rise at night rather than fall.
As a result, sleep is lighter and more disturbed, so we feel less rested even if we are spending the same amount of time in bed.
Critically, all these small shifts come at the exact time when our brains are facing the highest amount of strain.
Studies have shown that midlife is a period of maximum cognitive and emotional load as people step into leadership and caring roles.
Since mental multitasking drains energy as effectively as physical labour, people end up feeling completely exhausted even when they aren’t working physically.
However, Professor Spear points out that no two people will have exactly the same experience of ageing.
She says: ‘Midlife fatigue, in particular, often reflects cumulative load rather than ageing itself.
Energy levels rise again in our 60s, especially if we take care to maintain muscle mass through regular strength training (stock image)
‘Two people of the same age can have very different energy profiles depending on what their bodies are being asked to carry.’
The good news is that energy levels actually increase and become more stable in our 60s, even as our physical capacity declines with age.
Stress is lower, work is often less demanding, and our sleeping patterns typically become more regular.
Meanwhile, the mitochondria in our cells adapt surprisingly well into later life and can be improved through regular weight training.
Studies have shown that people in their 60s and 70s can use weight training to restore strength, improve metabolic health, and improve their energy levels within months.
Although you might not be able to do everything you did in your younger years, your 60s can bring more predictable energy levels with the right kind of care.
Professor Spears concluded: ‘The goal isn’t to recreate 20–year–old energy, but to protect and prioritise recovery.
‘That means regular sleep timing, resistance or weight exercise to preserve muscle mass, managing stress rather than just pushing through it, and fuelling adequately – especially protein intake.’
