The doctors stood at the end of my bed, looking mystified. I was terrified — I thought I was going to die. I’d arrived at hospital three days before with an internal temperature of 42C; now my organs were failing. As a GP myself, I knew how serious my condition was.

I was 39 with a wonderful husband, three beautiful children and a successful career but I didn’t have an immune system strong enough to fight this fever.

After four weeks in hospital I was eventually discharged with the unsatisfactory diagnosis of PUO — pyrexia of unknown origin — which basically means “you were very hot but we don’t know why”.

This was a life-changing moment. Whatever the diagnosis, the cause was clear to me: burnout. For years, I’d pushed my body to breaking point.

Determined to see my children, then aged ten, nine and five, grow up, I decided that I needed to use my medical knowledge to reinvent myself. The biohacks (as the data analysis and habits I deployed to optimise my health are called) have proved so successful that now, aged 53, my biological age — that is, the age of my cells, ascertained with a blood test that analyses protein markers of inflammation, central to ageing — is that of a 20-year-old.

Strange as it sounds, science shows we can bring our age down in a measurable way. I’m proof of this. And while biohacking might bring to mind wealthy tech titans trying to live for ever, many of the techniques I now teach clients as a longevity doctor are free, take minutes and can add decades to our lives.

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I believe we should set a goal for how long we want to live, just as we set goals for everything else, and work towards it. I tell clients that, with the right approach, there’s no reason they can’t make one million healthy hours, or 114 years. Unlikely as it might sound, that’s my intention.

Certainly, I feel barely recognisable from the partner in a GP practice who was too busy to go to the loo between patients, surviving on biscuits and writing prescriptions into the night after the children had gone to bed. I thought I could manage the juggle, never slowing down enough to notice the warning signs — constantly aching neck, waking up exhausted after four hours’ sleep — that I was about to crash.

I worked through the fever I developed one Friday morning in 2011 so as to not let colleagues down. But by the following afternoon I was too ill to eat, move or make decisions. My husband, Manish, a dentist who was then 42, rushed me to hospital near our London home where, thinking that my temperature must be caused by a severe infection, doctors put me on a potent intravenous antibiotic drip.

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When that didn’t help they performed emergency abdominal surgery in the middle of the night as they suspected that an abscess in my abdomen could be to blame. It wasn’t. Days later, weak from surgery and with my kidney and liver function deteriorating because of my continued high fever, there was still no discernible cause.

It was a month before my temperature stabilised and I was able to be discharged. Recuperating at home I realised that my body’s low resilience to stress after years of pushing myself to my limit had been to blame.

In addition to regaining strength, I prioritised rest, nutrition and movement, which I had long advised patients were essential but had ignored myself. I started with sleep. I set an alarm for 9.30pm to remind me to switch off screens before going to bed at 10.30pm and getting up at 6.30am. Back at work after four months off, I finally learnt to delegate. I filled up on protein and fibre, bought a standing desk, scheduled an appointment with myself at 12.30pm every day to go for a lunchtime walk or run and started lifting weights daily (I kept them under my desk at work).

As years passed and I felt stronger I realised there was more I could do to monitor my health than I’d learnt at medical school. I could identify the key factors that influence our biological age and test for them.

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These included hormones. I discovered that my levels of the stress hormone cortisol — which contributes to inflammation when raised — still weren’t dropping low enough at night to allow for deep sleep. I used light to regulate it, stepping outdoors on waking for a minute, and wearing glasses after 8pm that block the blue light emitted from screens that inhibits the release of the sleep-producing hormone melatonin.

A glucose test revealed that my blood sugar levels weren’t at optimum stability so I bought a continuous glucose monitor (CGM) — a device you attach to the back of your arm, available from chemists for around £50 — to track exactly what sent my blood sugar levels soaring via an app. Quinoa was an unlikely culprit for me, which certainly won’t be the case for everyone, but shows why monitoring individual data is important.

A DNA test revealed that my genes for endurance sport are stronger than my genes for strength. As I ran the London Marathon two years ago, I told myself I was “made for this” — not as a generic pep talk but because I was genetically programmed to keep going. It helped.

I numbered my most-used longevity biohacks from 1 to 10, with a correlating activity or time, to make them easier to remember. I don’t do all ten hacks every day but focus on a handful at a time, telling my clients that no matter how busy they are, everyone can find 60 seconds.

For example, 1-10 means spending one minute in morning sunlight followed by ten seconds setting an intention for the day; research has found people who have purpose live for seven years longer.

Meanwhile, 3-30 involves taking three sips of water every 30 minutes — one study found those with a lower fluid intake have a 21 per cent higher risk of dying prematurely — and 5-50 means holding five stretches for 50 seconds a day, including one related to balance; a study of 1,700 people aged 51-75 found people who couldn’t stand on one leg for at least 10 seconds had an 84 per cent higher risk of death after seven years.

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The 6-60 entails slowing your breath to less than six breaths a minute for one minute, every hour, as slow breathing has been found to lower our stress response.

Some of my strategies might sound extreme. I celebrated my 50th birthday alone and in silence in a cottage in the Spanish mountains for seven days, because silence is shown to lower stress and improve cognitive function. But everyone can achieve seven seconds of silence every 70 minutes (7-70).

Paying compliments, meanwhile, is important because it releases the bonding hormone oxytocin, which can help reduce feelings of loneliness. Oxytocin has been shown to light up the same centre of the brain as physical pain and may play a role in reducing inflammation.

I incorporate micro movements into my day — calf raises while I’m brushing my teeth, for example — and twice a week I have a sauna, because heat helps skin detox and stimulates the metabolism. I only eat between 10am and 6pm, as fasting encourages autophagy, or cell repair, and twice a year I do a water-only five-day fast, which sounds harder than it is. After three days your body’s hunger signals quieten down because it’s in clean-up mode.

My husband and children — now aged 24, 23 and 20 — are supportive and biohack themselves to a certain extent. They wear smart rings or bands like me to track their sleep data, heart rate and VO2 max, use sleep masks and mouth tape in the night, love exercise and sport, and have tested their gut microbiome and metabolism. They’re not fanatical about it but neither am I. Although I no longer drink alcohol, I still enjoy the occasional chocolate.

When I started to study longevity I felt I was getting my wrists slapped by colleagues in the medical profession. One GP said that telling people they could hack their health was dangerous. Disturbed by the semantics rather than the science, they thought I was suggesting people take extreme or unsafe measures. But what could be more important than taking control of your health?

Another said the role of GPs wasn’t to stop people getting sick, at which point, in 2019, I left conventional general practice to set up my longevity business. That was when I started testing my biological age, which has remained at 20 ever since. Helping to prevent people get as ill as I did and reverse ageing by 10, 20 or even 30 years feels amazing. I look younger now — my children joke that I blossomed late — but more importantly I have so much more focus, energy and joy, which I plan to maintain for decades.
As told to Antonia Hoyle