One in 20 cancers could be linked to radiation from CT scans. Now the world’s top scientists reveal how to protect yourself… and the act that makes the damage so much worse

A single abdominal CT scan can deliver a blast of radiation equal to 90 chest X-rays. I did not know that when I had one eight years ago, but it’s haunted me ever since.

Back then I was feeling inexplicably unwell, shedding weight – around a stone in six weeks – waking drenched in night sweats and so foggy-headed I could barely finish a sentence. Dizzy spells left me close to collapse. These are classic red-flag symptoms no doctor can ignore.

When initial blood tests showed nothing, my GP sent me for a CT scan of my abdomen and pelvis.

At the time it seemed the obvious next step. What I did not realise was that in just a few seconds my body absorbed 9.1 millisieverts of radiation, roughly equivalent to taking more than 100 transatlantic flights or having about 450 chest X-rays.

Those doubts returned with force this year, after a landmark study in JAMA Internal Medicine warned that the risks from CT scans may be significantly higher than previously thought.

It estimated the 93 million CT scans performed in the US in 2023 alone could trigger about 103,000 cancer cases: one in 20 cancers potentially linked to medical imaging we’re told is safe.

A CT scan is a fast, computerised X-ray that takes detailed pictures of your body in thin slices, a bit like a loaf of bread.

They’re especially useful for spotting problems in the chest, lungs, or stomach – and are often used in emergencies because they only take a few minutes, compared with up to an hour for an MRI. CT scans are also sometimes offered as part of private ‘health MOTs’.

CT scans use ionising radiation. This can break DNA strands in every cell directly and trigger inflammation which can lead to mutations, and, over time, cancer.

Or it can damage cells indirectly by creating highly reactive molecules called free radicals, which attack cell structures. (While free radicals are produced naturally through metabolism they’re also increased by pollution, stress, smoking, poor diet and radiation exposure, including from CT scans.)

CT scans focus concentrated bursts of radiation on a specific body area (often a vulnerable organ) and one ‘scan’ often involves several passes, so the same organs can be exposed multiple times. Many patients also have repeat CTs over months or years, and these doses have a cumulative effect.

Now some of the world’s top researchers, from Nasa scientists to Harvard University experts, are investigating ways to help the body repair the hidden damage caused by CT scans.

David Sinclair, a professor of genetics at Harvard Medical School and author of the bestselling Lifespan, has spent years studying what happens when DNA suffers tiny ‘breaks’.

These are little nicks in our genetic code that happen naturally as we age. When this damage builds up, the cell’s control system that decides which genes should be switched on or off can get scrambled. This mix-up is linked to faster ageing and a higher risk of diseases such as cancer.

Professor Sinclair believes the same kind of DNA disruption may be caused by CT scans, helping to explain why some people develop cancer after repeated CT scans.

‘If radiation-induced damage is not properly repaired, it can

lead to mutations, disrupted epigenetic signalling [i.e. which genes are switched on or off] and accelerated ageing,’ he says, adding: ‘I’ve never had a CT scan and would prefer not to unless absolutely necessary.’

Age plays a role in how our bodies handle scan-related damage.

‘Children are more vulnerable because their cells divide more rapidly,’ says Professor Amy Berrington, who leads the Clinical Cancer Epidemiology Group at the Institute of Cancer Research in London.

A major UK study in 2012 found that children who had five or more CT scans had a threefold increased risk of brain tumours and leukaemia later in life.

‘For certain groups – particularly young, healthy individuals – in our clinic we try to avoid CT unless absolutely necessary,’ says Professor Giles Roditi, a consultant cardiovascular radiologist at NHS Greater Glasgow and Clyde. But Professor Sinclair points out that older people also have more trouble repairing DNA, ‘so the same scan might pose more risk to a 70-year-old than to a 20-year-old’.

‘It is not just about radiation; it is about how your body deals with it,’ he says.

Smoking magnifies the damage, adds Professor Berrington, because it also harms cells. And some people carry inherited gene mutations that impair the repair process, so may face higher risks from the same radiation dose.

Women also have a slightly higher risk because tissues such as the breast and thyroid are more sensitive to radiation – and women generally live longer than men, giving radiation-induced cancers more time to appear.

People who are overweight often have more inflammation, which can impair DNA repair, adds Professor Berrington.

The good news is the body can usually repair this kind of harm. ‘Almost all DNA damage from a one-off scan is repaired quickly and efficiently,’ says Simon Bouffler, deputy director of Radiation Protection Sciences at the UK Health Security Agency (UKHSA).

After exposure, cells switch on protective systems, including DNA repair enzymes. According to the UKHSA, most damage either gets fixed or the affected cells die off.

But there are things we can do to help our body minimise any damage from a CT scan.

Professor Sinclair says the key is to build cellular resilience – making our cells more robust and able to recover from stress.

‘That means good sleep, exercise, time-restricted eating – and supplements that support DNA repair,’ he says.

Fasting is particularly promising for boosting cellular resilience before and after a scan, Professor Sinclair adds, as it triggers autophagy, a cell ‘clean-up’ that clears out damaged components.

He practises time-restricted eating, going 16 to 18 hours a day without a large meal. He points to research that shows going without food for part of the day doesn’t just cut calories, it changes how the body works, lowering insulin and IGF-1, a hormone that drives growth in childhood and wound healing – but in adulthood can block repair. Time-restricted eating also reduces inflammation and switches on autophagy.

Early clinical evidence is promising. In a 2024 study at the City of Hope cancer centre in California, patients having pelvic radiotherapy fasted for 12 to 14 hours around their treatment sessions and blood tests showed they had fewer signs of DNA damage.

Another proponent of fasting is Professor Valter Longo, a longevity researcher at the University of Southern California. He’s developed a five-day fasting-mimicking diet which replicates the health benefits of traditional fasting where you severely restrict food. Instead, on the first day, calories are capped at about 1,000 to 1,100, then drop to 700 to 800 a day for the next four days.

The meals are plant-based, with no protein and sugar, but include healthy fats such as nuts and olive oil. The aim is to nudge the body into repair mode while providing enough nourishment.

‘Because CT radiation contributes to DNA and other cellular damage by mechanisms similar to those caused by the normal ageing process, my fasting recommendations could help defend against these,’ Professor Longo told Good Health.

A 2020 study in Nature Communications found that women with breast cancer who followed a five-day fasting-mimicking diet while on chemotherapy coped better with treatment and showed stronger signs their tumours were shrinking than patients on a normal diet.

Professor Longo recommends doing his five-day regimen every three to four months, but also after scans.

Alongside this, he advises a predominantly plant-based Mediterranean-style approach that emphasises vegetables, legumes, wholegrains, fruit and extra-virgin olive oil. Red and processed meats, added sugars and refined carbohydrates should be kept to a minimum within time-restricted eating (keeping meals within a 12-hour window).

Regular activity is important both for cell resilience and post scans – physical activity switches on a key cellular regulator called Nrf2, according to a 2016 study published in Free Radical Biology & Medicine. This ‘master switch’ enhances the body’s antioxidant defences and helps cells neutralise free radicals.

There’s evidence that exercise makes DNA repair faster, too. In a 2019 trial reported in the International Journal of Molecular Sciences, people who exercised regularly were better at repairing DNA damage caused by radiation than those who didn’t.

Professor Sinclair also recommends boosting levels of NAD (nicotinamide adenine dinucleotide), a molecule in every cell that acts like a battery pack, fuelling enzymes that fix DNA and perform other vital repairs. NAD levels fall with age and illness.

‘Topping up NAD can improve DNA repair and boost cell resilience,’ he says.

The body makes NAD from vitamin B3 in foods such as poultry, fish, nuts and green vegetables.

Another option is supplements of NMN (nicotinamide mononucleotide) or NR (nicotinamide riboside), both derived from vitamin B3, which the body converts into NAD.

A 2022 study in Nature found that 12 weeks of between 250-600mg/day improved levels of NAD and muscle strength. Professor Sinclair takes 1,000mg of NMN daily.

Scientists say a simple vitamin might also offer protection. A 2019 study in the European Journal of Radiology found that taking 1,000mg of vitamin C just before an abdominal CT scan significantly blunted the spike in DNA-damage markers in blood cells.

And a 2024 review in the journal Antioxidants found 1,000mg of vitamin C an hour before a scan helps protect cells from the surge of free radicals created by radiation.

While other researchers are investigating vitamin D, melatonin and vitamin E, Nasa is testing whether the diabetes drug metformin could protect against radiation damage (a major risk posed by space travel – a deep-space mission can expose astronauts to the equivalent of 30 to 40 CT scans).

When mice were given metformin for three days before exposure to simulated cosmic rays, they showed far less DNA damage in bone marrow, lungs and colon tissue, and a 37 per cent higher survival rate, reported Plos One in 2024.

The researchers have now begun a human trial to test whether metformin offers the same benefits in patients.

If it works, a safe, cheap medicine could protect not only astronauts and cancer patients, but also the millions who undergo CT scans each year.

There is no doubt scans save lives, but knowing the risks means you can make smarter choices next time.

For me, that means asking if there is a safer alternative, or whether previous images will do the job.

It also means doubling down on habits that help the body repair – this way, we can limit the risks while still reaping the lifesaving benefits.