When we breathe the Sars-CoV-2 virus into our lungs, our immune system swings into action. If you are healthy, Covid infection and the destruction of lung cells triggers a local immune response. White blood cells including macrophages and monocytes are recruited, substances called cytokines are released, and adaptive T and B immune cells are primed.

In most cases, this process is capable of resolving the infection. But if you are unhealthy (if, for example, you are suffering from long-term illnesses such as obesity or diabetes) and/or you are older (say, over 75) and/or your immune system is impaired, or if your infection results from a huge viral load, then a very different story may unfold. There is likely to be an uncontrolled immune response – the release of a large dose of inflammatory molecules (a ‘cytokine storm’), a massive influx of immune cells to the infected area and a failure of the body to inhibit pro-inflammatory responses.

The cytokine storm mainly affects our lungs, and can lead to acute respiratory distress syndrome, eventually respiratory failure – and sadly, for many, death. It’s not only the lungs that are affected: many other organs are damaged, from the liver to the heart to the kidneys. This is both directly because of low oxygen, and indirectly by their own local inflammation and blood clotting. The brain is not exempt from this.

About one in five Covid patients show serious cerebral (brain) vascular events, such as strokes, TIAs and blocked blood vessels, as a result of circulating micro-embolisms (travelling blood clots) and increased clotting factors in the blood.

But further, we know now that during infection, the virus enters the brain as a kind of ‘Trojan horse’. It enters through the highly impermeable blood-brain barrier (BBB) – the tightly sealed blood vessels which protect the brain. The virus spike locks on to the ACE2 receptors of the vessels, replicates inside its cells and then passes through the BBB into the brain. Further, both local and body-wide inflammation conspire to break down the BBB, including damaging its communication with the immune system. There is some good news, however: it appears that though the virus gets into the brain’s neurons, it doesn’t kill them; and the insulation of white matter cells is left intact.

People recovering from Covid, or those with long Covid, talk about having ‘brain fog’ – a non-medical term used by people when they feel spaced out, sluggish or fuzzy. As well as the result of inflammation, this could also be because, as new research shows, the virus damages the mitochondria of our brain cells – the powerhouses of our cellular energy. Mitochondria make up 10 per cent of our body weight, and provide more than 95 per cent of our energy for all bodily functions, from fighting infection to metabolising food.

Is it all bad news, and is there anything we can do to fix our brains?

On an optimistic note, recent research shows that the mitochondria are extremely resilient. They have a double system of repair: via their own internal mechanisms, and via help from the cell nucleus.

It’s also within our power to look after our brains. Avoiding infection in the first place – chiefly by being fully vaccinated – is clearly the most important thing. But if you’ve had a Covid infection, you have some power over the preservation of mitochondrial function, and the recovery of your brain power. Since the outbreak of the pandemic, more than 20,000 scientific papers have been published. Thankfully, they show not only how we may defeat the virus but inspiringly, how we may counteract its effects.

The following measures are backed up by research:

Lower your calorie intake (but not your intake of nutrients)

This reduces the output of reactive oxygen species which drive inflammation and cellular damage. Aim to establish a healthy calorie range to prevent overeating – a reduction of about 10 per cent is recommended.

Fast intermittently

Intermittent fasting supports the mitochondrial network by removing damaged mitochondria and triggering biogenesis (manufacture) of new mitochondria.

Avoid regular sugar ‘boosts’

Astonishingly, certain neurons in the brain ‘feel’ a sudden rise in glucose levels (a ‘sugar rush’). Their mitochondria rapidly change their shape and structure and this can lead to profound overall metabolic change such as type 2 diabetes. Lowering the consumption of refined carbohydrates and sugars will remove this pressure on our precious mitochondria.

Eat healthy foods

Certain foods contain nutrients which support healthy brain cells by boosting their enzymes. Examples are omega-3 fatty acids (cold-water, fatty fish), alpha-lipoic acid (grass-fed red meat, liver, spinach, broccoli), and L-cartinine and creatinine (lean red meat, poultry, eggs, nuts, beans, seeds).

Take regular exercise

This will force your brain cells to generate energy, and is especially important as we get older, because there is an incipient loss of mitochondria as we age (1–2 per cent per year from middle age onwards). Exercise will reduce this trend and even reverses mitochondrial loss. After a period of consistent exercise mitochondria increase in number and are more capable of generating energy. Do what you can – from a brisk walk with the dog, to an hour’s hard work in the garden.

Take regular saunas

Try two or three times a week for 10-15 minutes at a time. Research has shown that increasing the temperature of muscle tissue increases the efficiency of mitochondria.

Get a good night’s sleep

This is about more than not feeling tired. Hormones such as corticosteroids, which act to regulate our mitochondria, are extremely sensitive to the disruption of our daily rhythms. Relaxation and meditation can play a part in keeping our mitochondria healthy by reducing the psychological effects of stress hormones, such as cortisol.

Try essential oils

Research has found that carvacrol, found commonly in the essential oils of thyme, oregano, black cumin and wild bergamot has been reported to inhibit the activity of ACE2 proteins – thus blocking the entry of the Covid virus – and has anti-viral, anti- inflammatory, anti-oxidant and immune-moderating properties.

Extracted from Supercharge Your Brain: How To Maintain a Healthy Brain Throughout Your Life by Professor James Goodwin, published in paperback on January 13, with a new chapter on Covid (RRP £10.99). Buy now for £9.99 at books.telegraph.co.uk or call 0844 871 1514