It's a never-ending battle between us and the germs that infect us, like the current evil virus Covid-19, writes Luke O'Neill
Your greatest friend in the battle against SARS-CoV2, the virus that causes Covid-19, is your own immune system. Its job is to keep you safe from nasty germs that might infect you and most of the time it does a great job. This is why 80pc of people will fight this virus with minor symptoms.
But sometimes your immune system isn't up to the job. This can be because you become infected with a massive dose of a virus, which runs amok and makes you feel awful. Or perhaps you are over 65 and, like most things in your body, your immune system is less able. Or you might be taking drugs that suppress your immune system if you have an inflammatory disease. Or if your heart or lungs are weak, the virus can really harm you. So the question is, is there anything you can do to boost your immune system? The answer is a resounding yes.
To know how to take care of your immune system, first you need to understand the weapons your immune system has, which are actually very impressive. When you come into contact with a germ you've never met before you've got various barriers to try to stop it getting into your body. As well as skin, you have mucus - snot is a really important barrier as it traps germs and has special biochemicals that can kill them, in this case mainly bacteria. Your body is also actually covered in bacteria, inside and out (bet you didn't know that), and many of these are beneficial. They out-compete the bad guys and even make chemicals to poison them. This stops the invader from eating the resident bacterias' lunch.
The germs can sometimes win, however. They have cunning tricks up their sleeves to breach the defences. A virus like SARS-CoV2 burrows inside the cells that line your lungs. That's where they multiply. However, pretty soon the rapid response unit of your immune system will arrive. Special white blood cells can attack the invader. So-called macrophages (which means 'big eater') eat the germs up and destroy them. They also call the alarm to bring out another white blood cell called a T lymphocyte. These are like police superintendents, controlling everything and even killing off the virally-infected cell themselves to stop the virus spreading. It's the T lymphocytes that remember, so that when you get reinfected they are good to go. T lymphocytes are an important aspect of why vaccines work. They also control another important white blood cell, the B lymphocyte. This is the cell that makes antibodies. These are very specific proteins that are great at stopping a virus like SARS-CoV2 in its tracks and B lymphocytes also remember.
We remain optimistic that there will be a vaccine soon. Vaccines are weakened forms of a germ or part of it, which causes a weak immune response. But the cells of the immune system are now trained. And when the intruder comes they kill it. It's a bit like the sheriff has put up wanted posters around town and when the bad guy turns up he's recognised and killed quickly and you won't even know you've been infected. This is why it's so important to get a vaccine for Covid-19.
The trick is to keep all these cells of your immune system fit and healthy. This begins with what you eat. A varied diet with lots of high-fibre foods really boosts your immune system - immune cells love healthy food and hate fatty foods, so a healthy diet is essential.
Also, if you don't over-eat and have good gaps between meals, this really mobilises the immune system increasing the numbers of immune cells by as much as three-fold, so lay off that second piece of pie and have gaps of at least four hours between meals. Don't over-do this, though, as being malnourished has a hugely negative effect, as can be seen in developing countries where it's a huge cause of death from diseases like TB.
The evidence for taking probiotic supplements is mixed. It's much more effective to change your diet to a healthier one.
Vitamin D has become a hot topic in immunology. It is used by our immune cells, and is something that people across the island of Ireland can get quite low on in the winter. So it's good to take in more of it. Taking extra vitamin C, however, is probably a waste of time for those who are well-fed. Eating your five-a-day of fruits and vegetables is the best way to maintain necessary levels. It's water soluble so you will just pass any excess into your urine.
To be immunologically fit, you also need to be physically fit. White blood cells can be quite sluggish. Exercise mobilises them by increasing blood flow in your body, so they can do their surveillance jobs and seek and destroy all over your body. Adults should be physically active in some way every day, and do at least 150 minutes a week of moderate aerobic activity (hiking, gardening, cycling) or 75 minutes of vigorous activity (running, swimming fast, an aerobics class). Either suffice.
The advice for older people, who are more vulnerable to infection, is to do whatever exercise is possible. Anything's better than nothing. But a lifetime's exercise could significantly stop your immune system declining with age. In 2018, a study found that 125 non-smoking amateur cyclists aged 55 to 79 still had the immune systems of young people.
Like eating, you can overdo it though. You can exercise to a point where it has a negative impact on your immune system. Elite athletes are more prone to infections. So don't overdo it. As ever, moderation is the key.
One of the many effects of exercise is that it reduces stress, which is next on our list of immune-boosting priorities. Stress hormones such as cortisol can decrease immune function, a common example of which is when chickenpox strikes twice. If you have had it, the virus never completely goes away. During periods of stress, it can reactivate again and you get shingles. And we all know that stress makes us more susceptible to colds and flus. Worrying about Covid-19 might actually make you more susceptible to it.
Forget boozing through the coronavirus crisis though, because heavy drinking also depletes our immune cells. This is one reason why alcoholics are more prone to infections. So the hot whiskey might make you feel better for a short time but it might also slow down recovery.
Exercising and eating well will have the likely knock-on effect of helping you sleep better, which is a bonus because a tired body is more susceptible to infection. A study last year found that lack of sleep impaired the disease-fighting ability of immune cells. If you've got a regular sleep pattern, you have natural body rhythms and everything's fine. If they go out of kilter, then you've got problems.
So the bottom line is a good night's sleep, combating stress, a balanced diet, and moderate exercise are all great at boosting your immune system, in the never-ending battle between us and the germs that infect us, and that includes the latest bundle of evil, SARS-CoV2. Stay healthy.
Luke O'Neill is professor of Biochemistry in the School of Biochemistry and Immunology at Trinity College Dublin