Your immune system is your body's natural defence, protecting you from bacteria, viruses and other harmful invaders. Every shelf in the pharmacy promises to boost it, and every winter, a new tea, powder or gummy claims the job. If any of them worked as promised, you would be sneezing at pollen in the next county.
Here is the problem with that word. An immune system can go wrong in two directions, and only one of them is weakness. The other is an immune system that fires too hard, at too much, and that is not something anyone should want to boost.
So here are seven rules with a different aim. They are about what your immune system is built from, what wears it down, and how to keep it balanced. Small, everyday choices are most of it. A few of them will change what goes on your plate.
1. Stop trying to boost it
When the immune system overreacts to something harmless, like pollen or a food, the result is an allergy. When it turns on the body's own tissue, the result is autoimmune disease: rheumatoid arthritis, type 1 diabetes, lupus, Hashimoto's thyroid disease. In each case the immune system is not weak. It is too busy, aimed at the wrong target. Think of a bouncer who throws out the band.
Why it overreacts is partly a matter of training. Unconventional Remedies for Chronic Allergies has the Amish children raised among farm animals, whose asthma was four times and allergies six times less common than in children from farms run with modern machinery. An immune system that meets the real world early learns to stay calm in front of it.
So the goal is not more. It is the right amount, at the right moment, switched off when the job is done. For a readable tour of how the system decides when to fight and when to stand down, try .
Fever is a good example of the system doing exactly that. A raised temperature is not the illness. It is part of the defence, a deliberate change in the body's thermostat that makes life harder for the germs. Bringing it down makes you more comfortable, and it does not seem to change how the illness turns out, for better or for worse. A fever in a baby under three months old, or in someone whose immune system is already weak, is a different matter and needs checking straight away.
Fever has even been used as a treatment in its own right. In 1927, Julius Wagner-Jauregg won the Nobel Prize for deliberately infecting patients with malaria. The fever it brought treated late syphilis of the brain, years before penicillin. It was called pyrotherapy, healing by fire, and it was crude, but it shows how seriously the body means its fevers.
The old saying "feed a cold, starve a fever" was first printed in a dictionary in 1574, and the idea behind it is credited to Hippocrates, who thought that starving a fever starved the disease. The only test of the saying itself, in the Netherlands in 2002, involved six men. Eating raised a signal the immune system uses against viruses, and fasting raised one it uses against bacteria. Six men settle nothing, but the hint was interesting.
Losing your appetite when you are ill is part of the same defence, along with the sleepiness and the urge to be left alone. In mice, it seems to matter which germ is involved. Mice with a bacterial infection survived better when they were left to go without food, and feeding them sugar killed them. Mice with flu did the opposite: food, and sugar in particular, kept them alive. That is mice, not people, but the old saying may have half a point.
Your body also hides its iron when you are ill. During an infection, the liver releases a hormone called hepcidin, which locks iron away inside cells and cuts how much the gut takes in. Many germs need iron to grow, and starving them of it is part of the fight. Hepcidin was first named in 1998, because it seemed to kill bacteria.
A strong immune system, then, is a well-supplied one. That is what the next three rules are about.
2. Feed it protein
Your immune system is built out of protein. Antibodies, the molecules that recognise and tag invaders, are large proteins, shaped like a Y. The white cells that carry them, and the chemical signals they send each other, are made from protein too. Every infection means building more of all of it, fast. You cannot build an army out of salad.
Even your first line of defence is made of protein. In 1922, Alexander Fleming, who later discovered penicillin, showed that nasal mucus kills bacteria, and named the substance responsible lysozyme. It is an enzyme, it is in your tears, saliva and mucus, and it dissolves the walls of certain bacteria on contact. Egg white carries large amounts of it, which is how its germ-killing power was first noticed, in hen eggs, in 1909.
Run short of protein, and the defences thin. Malnutrition weakens the immune system, and people who do not get enough protein and energy pick up more infections.
The best protein for the job comes from meat, fish and eggs. They carry all the amino acids your body cannot make for itself, with no fibre or plant compounds getting in the way.
3. Get your minerals from meat
Zinc is the mineral your immune cells cannot work without. When zinc runs low, immune function falls, and infections of the chest and gut, pneumonia among them, become more likely.
We learned how much it matters from Iran. In 1963, a report described a 21-year-old Iranian man whose growth had stalled, still with a boy's body, and anaemic on top. All of it reversed when he was given zinc. In 1972, fifteen young Iranian men rejected by the army showed the same signs, and every one of them responded to zinc.
The richest food sources of zinc are oysters and meat. A tin of in the cupboard makes the oyster part easy. Grains and beans carry phytate, which holds on to zinc in the gut. A diet built on bread and beans can run short of zinc even when the numbers on the packet look fine. Why Your Fruits and Vegetables Deliver Less Than You Think has more on what phytate locks away.
Nutrient Deficiencies: Who's at Risk and Which Test to Get has why zinc has no reliable single blood test, which makes the plate the practical check.
Selenium has an even stranger story. In parts of China where the soil is poor in selenium, a disease that weakened the heart muscle was traced to two things together. One was too little selenium, the other a common virus. Without enough selenium in the people it infected, a more dangerous strain of the virus seems to have taken over. Adding selenium to the diet brought the disease down.
The Quiet Signals of Mineral Deficiency has the soil side of that story. Selenium comes mainly from meat, with kidney, tuna, crab and lobster among the richest, and from eggs.
4. Get enough vitamin A
Vitamin A keeps the immune system working and the eyes seeing. Where it runs short, around the world, the result is hundreds of thousands of cases of blindness, and of children dying of ordinary childhood illnesses because their immune systems failed.
How much it matters shows up most clearly where it is scarce. Across 19 tests covering more than 1.2 million young children, mostly in poorer countries, those given vitamin A were 12% less likely to die from any cause than those who were not.
In a well-fed adult, vitamin A shortage is rarer, but the lesson holds. The ready-made form your body can use straight away comes from animal foods: liver above all, then eggs, butter and oily fish. Plants carry carotenes instead, such as the beta-carotene in carrots, which the body has to convert into vitamin A before it can use them.
5. Look after the gut
The old claim that most of your immune system lives in the gut turns out to be true. The lymphoid tissue along the gut makes up almost 70% of the entire immune system, and about 80% of the cells that make antibodies sit there.
That makes sense. The gut is the biggest surface where the outside world meets the inside of your body, every meal, every day. The immune tissue along it has to tolerate food and the friendly bacteria, and still catch anything dangerous that comes in with them.
So what irritates the gut keeps that tissue busy. Indigestion? Your Stomach May Need More Acid, Not Less has the plant foods that ferment and bloat, and why enough stomach acid is an early defence against the germs that arrive with food. A calm gut is a gut whose immune tissue can do its real job.
6. Keep blood sugar down, and alcohol rare
High blood sugar slows the white cells that hunt bacteria. Even short spells of it make them worse at moving towards a germ, swallowing it and killing it. People with type 2 diabetes, whose blood sugar runs high for years, pick up more infections than people without it, at every body weight. Why You Keep Getting Sick, linked below, has why low-carb eaters may catch fewer colds.
Alcohol works in two stages. When volunteers drank to the level of a binge, their immune cells surged within 20 minutes. Two and five hours later, the picture had flipped: fewer of the cells that kill infected cells, and a weaker response to bacteria. One big night out leaves your defences down for the hours that follow, which is not the moment you want to share a crowded room. Hangover, meet head cold.
Smoking belongs on the same list. It weakens the immune system, which leaves smokers more open to infections and slower to recover from injuries.
Sweets and sweet drinks are the easiest place to start. Neither has a role in a strong defence.
7. Sleep, sun, calm and company
The rest of the list is well known, and it holds up.
Sleep is the biggest lever. People given a cold virus on purpose were about four times as likely to catch it if they had been sleeping less than six hours a night. The Sleep-Immune Connection, linked below, has what a single bad night does.
Long stress lowers the defences, and a hard month does far more damage than a bad day. Chronic stress can wreak havoc, and it shows up as more colds.
You don't have to become a marathon runner. Moderate movement on most days goes with fewer and milder colds, while punishing training does the opposite: runners who finished a marathon were far more likely to fall ill in the week after the race than similar runners who stayed home.
Age wears the system down slowly as well, which makes everything in this article matter more with every decade. Defy Aging with Movement: How Exercise Keeps You Strong, Sharp, and Independent for Life has the lifelong cyclists aged 55 to 79 who were still making new immune cells at the rate of young adults.
Get outside. Sunlight on your skin makes vitamin D, and low vitamin D goes with more chest and throat infections. Shade and a hat protect you on a long day out, but a short spell of sun on bare arms is how the body was built to get it. The sun has never once been out of stock.
And keep people around you. A life with many kinds of company, family, friends, neighbours, a club, goes with fewer colds, even though it means meeting more germs. Why You Keep Getting Sick has all of these in full.
The defence you build
Taking care of your immune system is about consistency in everyday habits rather than drastic overhauls. Protein, zinc and vitamin A from meat, fish, eggs and liver give it the materials. Low blood sugar, little alcohol, a calm gut, sleep, sun and company stop it being worn down.
None of it comes in a bottle with "boost" on the label. The power to strengthen your immune system is in your hands, and most of it is on your plate.
This week, put liver on the menu once, and swap one sweet drink a day for water.
Catching every cold going? Why You Keep Getting Sick: The Causes of Frequent Colds — the people around you, sleep, stress, movement and the gut, and what to do once a cold has started.
Short on sleep this week? The Sleep-Immune Connection: What One Sleepless Night Does to Your Defences — where the line falls for colds, why being ill makes you sleepy, and sleeping through a cold.
Know someone with a cupboard full of immune-boosting gummies? Send them this, and a tin of oysters.
Disclaimer: This article is general information. For advice about your own health or immune system, talk to a qualified health professional.
Affiliate Disclosure: This article contains affiliate links. As an Amazon Associate, All For Life earns from qualifying purchases, at no extra cost to you. We only link to products we would recommend without the commission.
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