Michael Mosley throughout his astonishing last documentary

In the final documentary fronted by the late Dr Michael Mosley, the health guru was filmed putting on a joyful display as he enjoyed a cold water swimming session.

Filmed last year, the three-part Channel 5 programme sees the former Mail columnist decode the marvels of the human body – and discover everything from why bones break as we age, to pioneering cancer treatments.

Dr Mosley, who died from heat exhaustion aged 67 while on holiday in Greece, put his own body under the microscope for the documentary.

In the first episode, which was at 8pm on Thursday, the doctor bravely signed up to face the elements while taking a cold water swim.

Dr Mosley explained how he was attempting a very fresh dip in the water for its benefits in supporting bone health.

‘Weight bearing exercises are a great way to keep your bones strong but other forms of exercise, like having a swim, come with benefits,’ he explained. 

Dr Mosley then headed to the Ayrshire coast to meet some cold water devotees during the programme.

‘When you first get in you think, what on earth am I doing, it’s freezing,’ confessed one Scottish woman who was seen together with a group of ladies doing some warms up before facing the temperatures in the sea. 

While tricky at first, the cold water swimmer described the teeth chattering ritual as ‘absolutely liberating,’ while another called it ‘magic’.

The brave group of cold water swimmers were seen gliding through the freezing water with brave faces, grinning and splashing around as they took the chilly hit.

Using a thermal camera, swimmers were able to check their internal temperatures before taking the plunge.

Dr Mosley explained the change. ‘Their skin started off at around 22 degrees but after just 15 minutes… our thermal camera reveals their skin temperature has dropped to 10 degrees, almost as low as the sea.’ 

‘We hear a lot about cold water swimming, but what actually happens to your body when you go in cold water? What are the health benefits and what are the risks?’ he asked. 

Dr Mosley revealed that when you swim in cold water, your arteries narrow – making your heart work harder to pump blood, strengthening its muscles. 

The plunge also releases hormones that are said to increase the body’s metabolic rate and boost your mood. 

Some regular swimmers even claim it helps with immune function as well – stopping them, ironically, from catching common colds. 

Heading back to London, Dr Mosley went to try the chilling technique himself, arriving at a cold bath in the capital fully kitted out in a wetsuit. 

‘I feel a bit of a fraud I must admit because I’ve got all this on at the moment,’ he confessed before the physiologist onsite assured him it would still work through the layer.

Dr Mosley asked how he needed to approach the plunge before being told to embrace the cold slowly to avoid overworking and stressing the heart.

‘You’re a tropical animal, you want to be in 28 degree air and you’re taking that body and plunging it into 12 degree water, it’s a stress!’ explained the expert.

As he dipped a toe in the pool, Dr Mosley couldn’t help but yelp, ‘that is cold!’ before moving in slowly to gather his breathing.

Amid pained giggles, Dr Mosley went as far as his thigh and clasped his arms round his shoulders.

After he acclimatised to the chill, Dr Mosley confidentially took off in a breast stroke, breezing across the pool despite the cold temperature on his skin.

Elsewhere in the documentary, Dr Mosley headed to Fife to meet Thomas, who suffered a common neurological condition, and was about to undergo pioneering brain surgery.

The 71-year-old suffered essential tremor, which affects roughly a million Brits and causes involuntary shaking or trembling.

But for Thomas, symptoms began in his forties, when he first noticed his right hand shaking. 

By his mid-fifties, both hands, as well as his head, were shaking – and it just continued to worsen.

In the documentary, Thomas was off to Dundee to receive a potentially life-changing surgery. 

The innovative procedure uses a beam of ultrasound waves to zap a tiny cluster of cells in a part of his brain called the thalamus, which is involved with movement.

Doctors hope this will create a circuit breaker that will stop Thomas’s brain from sending out too many confusing messages that cause his uncontrollable tremor. 

Fitted with a head brace to help keep him still, Thomas was kept awake throughout the surgery to ensure the beam doesn’t impact the parts of his brain that control his speech. 

If it strays even a fraction, he could be left unable to speak – or paralysed. 

To test his brain function after each round of the ultrasound, Thomas’ doctors drew him a spiral on a piece of paper. 

At first, he was barely able to make a mark on the page. But after seven rounds, his hand stopped shaking enough that he is able to make a full spiral.  

‘I’m so grateful,’ Thomas said – ‘I noticed a change right away. I’ve improved way more than I thought I would. It’ll make a life-changing difference.’ 

Later in the episode, Dr Mosley met 76-year-old Allen, who was about to learn if his experimental cancer treatment has been a success. 

Allen was diagnosed with stage 4 lymphoma – a type of blood cancer – a few years prior. 

‘They said that there wasn’t really much they could do to cure me,’ he explained. 

Prior to his diagnosis, Allen was a policeman in London, and spent nine years as Princess Diana’s personal protection officer. 

He started noticing symptoms of his cancer once he’d retired to Dorset, around the same time a family of Ukrainian refugees came to live with him. 

After his diagnosis, they decided to stay and help care for their host.  

‘I’d already planned and paid for my funeral,’ Allen said.  ‘I didn’t think I’d be around much longer.’

But then, Allen was thrown a lifeline by his medical team in Southampton; a treatment known as CAR T-cell therapy. 

The revolutionary new cancer treatment works by boosting the body’s immune system, helping it to spot and fight cancer. 

T-cells – the body’s fighter cells – are removed, modified in the lab and re-injected into the bloodstream. 

These genetically edited cells now have a turbo-charged ability to track down and eradicate cancer cells. 

The approach doesn’t work for everyone, but Allen luckily received brilliant news at his check-up; he was in complete remission. 

Previously littered with cancerous tumours, his scans are now showing up clean.

Thanks to breakthrough treatments like this, Dr Mosley explained, we’re now six times more likely to survive cancer than we were 40 years ago – although one in two of us will be diagnosed with it in our lifetimes. 

Similarly astonishing technologies have emerged in recent years that tackle another major health concern for Brits – heart disease.  

Almost a quarter of all deaths in the UK are due to cardiovascular problems.

But a new test developed by researchers at the University of Oxford claims to be able to detect heart problems long before you have any symptoms. 

By looking at the fat that surrounds the heart vessels, scientists are able to spot early signs of inflammation in the arteries, which could indicate a heart attack later down the line.

 To test it out, Dr Mosley stepped forward for the procedure – which saw him have dye injected into his bloodstream so that his arteries showed up on the CT scan. 

Finally, Dr Mosley examined why our bones become more brittle as we age. 

To investigate bone health, he travelled back to the University of Oxford – this time to meet with Professor Sue Black. 

She explained that bones – while they may look solid from the outside – are actually very much alive and moving on the inside. 

As we age, the hormones such as estrogen that feed these bone cells begin to lessen. 

After menopause, however, estrogen levels drop – causing the bones to become rapidly weaker. 

Microfractures begin to form, which often fail to heal themselves.  The condition – known as osteoporosis – is incredibly common: affecting one in five women and one in 20 men.  

To protect our bones as we age, we need to consume plenty of calcium and vitamin C – as well as continuing to do weight-bearing exercises like running and dancing.

The episode concludes with Dr Mosley agreeing to have a camera inserted through his nose to look at his voicebox – and revealing the shocking fact that humans produce enough saliva each month to fill an entire bathtub. 

In the next installment of the docuseries, he’ll look at hip replacements, stress and three things you can do at home to reduce blood pressure without joining a gym.