New Scientist - USA (2020-09-12)

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similar for the innate arm of the immune system,

especially among people living at latitudes where there

isn’t enough winter sunlight for their skin to synthesise

the molecule. A 2017 review of the evidence for taking

vitamin D supplements concluded that it helps prevent

upper respiratory tract infections. About 1000 to 2000

IUs should be safe and beneficial, says Wu, but people

shouldn’t go higher than that because, once more, big

doses actually suppress T-cell function.

But maybe popping pills isn’t the best approach.

Exercise is a proven immune-boosting strategy. It keeps

the thymus youthful, the heart-shaped patch of

lymphatic tissue, located beneath your breastbone,

where new T-cells mature before being released on

active duty. T-cells are pivotal in the adaptive immune

response, the more targeted part of the system.

The thymus degenerates with age, and our T-cell

count with it, with consequences for our ability to fend

off new pathogens. However, when Janet Lord at the

University of Birmingham, UK, and her colleagues took

blood samples from 125 amateur cyclists aged between

55 and 79, many of whom had been regularly riding

long distances for decades, they found that their T-cell

counts were similar to those of much younger people

and their thymuses were youthful.

Exercise is also good for our neutrophils, a crucial

first line of defence against bacterial invaders. When

bacteria are detected, neutrophils squeeze out of the

blood vessel and barrel towards their target, engulfing

them like Pac-Man, spraying them with deadly

chemicals, or disgorging their DNA and throwing it

around the invaders like a net.

The ability of neutrophils to tunnel through tissues

and find their target becomes increasingly erratic as we

age. Older neutrophils can still detect invaders, but

often blunder haphazardly through tissue or charge off

in the wrong direction. Not only does this reduce the

speed and efficiency of the immune response, it can

also result in friendly fire – a leading cause of the

generalised low-grade inflammation that creeps

throughout our bodies as we age.

In a separate study, Lord and her colleagues

measured exercise levels and neutrophil migration in

211 older adults, and found that those doing 10,000

steps a day on average had neutrophils as good as those

of young adults. Neutrophils don’t kill viruses, so they

won’t prevent you from catching diseases like covid-19

or influenza, but they will shore up your defences

against bacteria – including helping to protect against

secondary infections, such as bacterial pneumonia. ❚