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The COVID-19 crisis has got us all thinking more about our immunity. What protects some of us from illness and infection? And what puts others at increased risk?
For many of us – who feel young at heart – it may have come as a shock to learn that our seemingly robust immune systems are suffering from a problem that we can do little about: we're not as young as we used to be.
You may only become aware of your immune system when it swings into action to fight an infection – that scratchy sore throat and tickly nose are signs that it's detected a virus and is fighting it off. But, behind the scenes, this complex network of organs and cells is always on the warpath.
"It is a silent wonder – and your most precious asset when it comes to maintaining good health," says Dr Jenna Macciochi, a lecturer in immunology at Sussex University, and author of Immunity: The Science of Staying Well (Thorsons). "Your immunity is as unique to you as your fingerprints – the reason some viruses leave you untouched while others knock you flat."
But, even if you are one of those people who never catches a cold, your immune system is being eroded as you age. Our thymus gland – responsible for producing T cells, immune warriors that help us fight off viruses – is shrinking (one reason that vaccines may not work so well either as you age).
Meanwhile, our telomeres – the caps at the ends of our chromosomes that are a bit like the sheaths on the ends of a shoelace – are also likely to be getting shorter, meaning they're less able to protect our immunity.
The health of our digestive tract – home to 70 per cent of our immune system – may not be as good as it once was.
Our ability to secrete digestive enzymes tends to decrease with age, in some cases due to a condition called atrophic gastritis, which affects almost 25 per cent of people in their 60s and 40 per cent of over 80s.
Atrophic gastritis can reduce the absorption of certain nutrients, including vitamin B12 and calcium, which is why it's important to look out for multivitamins that are specially formulated for older adults.
"Globally, significantly more men die from infections," says Dr Macciochi 1 . "It's generally thought that women have evolved to develop a better immune response to infection in order to look after their young.
Female sex hormones also have a role to play, with oestrogen activating the cells involved in an inflammatory anti-viral response, while the male hormone testosterone suppresses it."
Despite all this potentially gloomy news, don't buy into the idea that your health will inevitably decline as you get older, says Dr Macciochi.
"There are things we can all do to keep our vitality and prepare our bodies for a longer, healthier life."
Boosting your diet with fibrous foods from a plant-based diet – with a wide range of fruit, vegetables, nuts, seeds, legumes, wholegrains, and herbs and spices – helps increase levels of healthy bacteria in the gut, in turn improving your immune response.
Aim for the recommended 150 minutes of cycling or walking every week, together with muscle-strengthening exercises on two or more days.2
"Exercising regularly has been shown to protect your immune system by lengthening your telomeres – and the longer they are, the stronger your immune system will be as a result," explains Dr Natalie Riddell, lecturer in Immunology at Surrey University.
Being overweight, especially with too much visceral fat (the fat around your belly and internal organs that is linked to chronic inflammation), has been linked to worse outcomes from COVID-19.
"But that could also be because people with too much of this kind of fat often also have other illnesses that tend to go hand in hand with excess visceral fat, such as hypertension or type 2 diabetes, that play into these worse outcomes," explains Dr Macciochi.
"Much less research has been done into the effects of having too little body fat," continues Dr Macciochi, "but we do know that fat is an important storage site for the cells that remember past infections. With too little body fat you may not have enough space for memory cells. So, it's quite important for our defences that we carry enough body fat, but not too much."
If you don't already get a good night's sleep, now's the time to polish up your sleep hygiene with a good wind-down routine.
One study found that just one night of poor sleep – six hours instead of the usual seven or eight – significantly reduced immune function compared to those who slept well.3
The following vitamins and minerals all have a role to play in keeping your immune system in top condition, says Dr Macciochi:
Vitamin C won't prevent you from catching a cold, but taking one to two grams daily can reduce symptoms and severity, and decrease recovery time.
Vitamin D normally derived from exposure to sunlight, has been shown to help the immune system fight off bacteria and viruses, and a deficiency – especially likely in winter – makes you three to four times more likely to catch a cold.
Zinc bolsters your defence against infection but becomes harder to absorb as you age.
Vitamin B12 helps with the production of white blood cells, which are essential for an efficient immune system.
Karen is a freelance health journalist and author/editor of 14 health books. She is a member of the Medical Journalists' Association and her features have appeared in various publications including Woman's Own and the Guardian.
Find out more about Karen Evennett.
1Ubeda, F. and Jansen, V. A. A. (2016). The evolution of sex-specific virulence in infectious diseases. Nature Communications 7
2Bartlett, D. B. et al. (2017). Neutrophil and monocyte bactericidal responses to 10 weeks of low-volume high-intensity interval or moderate-intensity continuous training in sedentary adults Oxidative Medicine and Cellular Longevity
3Taylor, D. J. et al. (2017). Is Insomnia a Risk Factor for Decreased Influenza Vaccine Response? Behavioural Sleep Medicine 15(4)