MICHAEL MOSLEY: The test that reveals Covid has made us more stupid

Are we becoming slower-witted? The answer should worry all of us.

A few years ago I made a TV programme called The Great British Intelligence Test where we measured the brainpower of the nation and ­carried out the largest intelligence experiment of its kind.

More than a quarter of a million ­people took our special IQ Test, developed for us by scientists from the Department of Brain Sciences at Imperial College ­London. (You can see what we put ­people through by searching online for ‘Michael Mosley IQ test’.)

We discovered, unsurprisingly, that when it came to problem-solving, ­people in their early 20s did the best; they have more knowledge on their side than, say, a teenager, but their brains are also working faster than people who are middle-aged or older.

The reason problem-solving ability falls with age is, in part, linked to how well insulated the connections are between your brain cells.

Dr Michael Mosley made a TV programme called The Great British Intelligence Test

As we age, the myelin sheath that ­surrounds the brain’s wiring gets ­thinner and communication between our neurons slows. Our brains quite ­literally slow down.

But there was some good news for older people; while other cognitive skills decline with age, verbal ability increased, peaking in people in their 70s. Oddly enough, cat lovers scored higher on verbal ability than dog lovers (though that may have been chance), as did book readers and people who are fond of fruit and veg.

But the biggest surprise came much later, long after the programme had aired on TV.

That’s because the test was put online in 2019, before the Covid pandemic swept the world, and the researchers continued to ­collect data well into 2020, when the outbreak was at its worst.

By this point they’d included questions about whether people had had Covid and, if so, how it had affected them.

They found that people who had been infected scored lower on the IQ tests, particularly when it came to something called ­executive function, a measure of ­mental skills such as memory, ­flexible thinking and self-control. If your executive function is affected, this can make it hard to focus, follow directions and ­handle emotions.

The team have since completed a larger study involving more than 112,000 people, which was published last month in the New England Journal of Medicine.

This confirmed the long-term impact that Covid can have on our brains. People who had a mild infection lost a couple of IQ points, but those who developed long Covid saw an average fall in IQ of about six points.

And the results of this study fit in with another more worrying trend, which is that IQ scores have been falling worldwide since the 1970s. In a 2018 study ­published in Proceedings of the National ­Academy of Sciences, researchers looked at the IQ scores of young men in Norway, recorded when they were ­conscripted for compulsory ­military duty. Over a 40-year period, beginning in 1970, there was a steady decline of about seven points per generation.

This phenomenon has since been recognised in other ­countries, including the U.S. and the UK.

While no one really knows exactly what’s going on, there’s a suggestion that it could be to do with rising levels of obesity and our growing reliance on ultra-processed food, both of which are bad for the brain.

Being struck down by an ­infectious disease, particularly one that persists (like Covid), is also a surefire way to reduce your IQ score.

There is also a growing concern, among some researchers I’ve ­spoken to, that the rise in ­artificial intelligence will add to downward pressure on human intelligence, as we increasingly rely on machines to do our ­thinking for us.

So what can you do to keep your brain in good shape?

There is plenty of evidence that eating a healthy diet can make a big difference. A study of 70-year-olds by ­Edinburgh University in 2021 found that those who were eating a Mediterranean diet (rich in olive oil, nuts, veg and fish) scored highest on a range of memory and thinking tests.

More surprisingly, playing ­computer games also seems to be good for improving your cognitive skills. That’s ­certainly what we found in The Great British ­Intelligence Test — a finding backed up by a recent, more ­rigorous study, ­published in JAMA Network Open in 2022.

Scientists at the University of Vermont looked at data from nearly 2,000 children and found those who reported playing fast-action video games for three hours a day or more did better on tests of impulse ­control and ­working memory than ­children who claimed never to play video games.

Not only that, but brain scans showed they had greater activity in regions associated with ­attention and memory, the result of all those hours spent trying to shoot things and avoid being shot.

And last, but by no means least, do keep challenging ­yourself mentally. There is plenty of evidence that taking up new hobbies, like ­dancing or painting, will keep your brain young.

Conversely, withdrawing from the world can lead to brain shrinkage, reduced brain cell ­connections and even falling ­levels of hormones in the brain that are essential for long-term repair and maintenance.

I intend to do what I can to keep my neurons going for as long as possible and, as poet Dylan ­Thomas put it, to ‘rage, rage against the dying of the light’.

One of the hardest things to treat is a chronic wound, like those caused by type 2 diabetes.

Now researchers at ­Sheffield University are using ionised gas (gas with an ­electrical charge) to treat chronic wounds: the gas ­creates a chemical cocktail in the wound, helping to kill bacteria and speed up ­healing. With antibiotic resistance on the rise, this could be a game changer.

Your dog really does understand 

Our dog, Tari, died a couple of months ago, and I still find myself shouting ‘walkies’ as I head for the front door, forgetting she is no longer around.

I’ve often wondered whether she understood the word ‘walkies’, or whether it was my tone of voice and behaviour (i.e. the fact that I’d be standing by the front door with a lead in my hand) that gave her the clue.

A recent study suggests that dogs understand us better than we think. Researchers at Eotvos Lorand University in Budapest monitored dogs’ brain waves when they heard their owners say words they assumed the dogs knew, such as ‘ball’. 

They found that when the dogs were given a toy that matched the word their owner said, their brain activity was different from when they were given something that didn’t match it.

The researchers said this is proof that dogs actually understand the meaning of words. Our canine friends are even more remarkable than most of us already believe.

Bitter-tasting veg may boost your mood 

Many people struggle with eating bitter green vegetables such as kale, chard and chicory. Yet these are particularly good for us — and here’s more about why.

Bitterness is one of our five ‘basic’ tastes (the others are sweet, salty, sour and umami. Humans are ­particularly sensitive to bitter ­flavours, probably because bitterness is often associated in the natural world with poison, something to be avoided.

Yet bitterness is also a sign that food is rich in beneficial plant compounds called polyphenols. Recent research by Shibaura Institute of Technology in Japan provided ­fascinating insights into why polyphenols are so good for us. 

They point out that we have taste receptors throughout our body. You find them, for example, in the gut, where they respond to polyphenols you’ve eaten by releasing hormones that improve your blood sugar levels and your mood.

Men even have similar sensory receptors in the testicles that seem to play a role in the production of healthy sperm. That could explain why men who eat lots of bitter, leafy, green vegetables tend to have higher sperm counts and better sperm motility. 

Something to bear in mind next time you are shopping for veg.