I’m an immunology expert – loading up on Vitamin C won’t stop a cold

Good immune health is vital, and without it we could succumb to any number of infections and illnesses. For example, take the tragic situation of David Vetter, famously known as the boy in the bubble. Born in 1971, with a severe immune system problem, he spent his whole life in a Texas hospital in isolation.

Though he remained relatively free from exposure to germs, he died, aged 12, from cancer caused by a virus. Another thing we can be certain of is that immune health is complicated. That’s partly because our immune system must fight so many different germs, including bacteria, viruses and fungi, each of which must be detected and destroyed in lots of ways so that it is hard for germs to evade the attack. On top of this, we also need the immune system not to set about attacking any of the body’s healthy tissues and cells.

How does your immune system really work?

A simple way of putting it would be that the immune system fights off anything which is not part of the human body. But this can’t be true – or at least not the whole truth. Granted, germs are not part of the human body, and dangerous ones should be killed. But food is not part of the human body either and we don’t want the immune system to react against harmless varieties.

Plenty of germs are harmless, too. In fact, there are billions of bacteria living in your gut that are beneficial, and we don’t want the immune system to react against the normal, resident kind. As a result, the immune system is a multi-layered and complicated system involving all sorts of different cells, protein molecules and genes.

If the immune system is boosted too much, the body’s normal healthy cells and tissues can be attacked. Indeed, some diseases are themselves caused by an unwanted immune response against the body’s normal cells.

Autoimmune diseases include multiple sclerosis, rheumatoid arthritis, systemic lupus and type 1 diabetes. In all of these, the immune system mistakenly reacts against the body’s healthy cells and tissues. To tackle autoimmune diseases, we want to dial down the activity of the immune system – but not too much, or we risk the immune system no longer responding well to an actual threat, say from a viral or bacterial infection. So, good immune health is about having the human body respond to a genuine threat, with precision and to the right extent, with minimal collateral damage. Which brings us to another vital backdrop to immune health.

We’re not all the same

We vary in how susceptible we are to every kind of illness, and in symptoms we experience and with every type of infection. It’s inevitable that some people are going to be more susceptible to this season’s cold viruses or feel its effects more than others.

Variation is also true for how we live. Certain lifestyle choices might be generally bad, others beneficial. But some things are likely to benefit you more than me. Others will be especially bad for me, and not you. Everything is personal. There is no “one-size-fits-all” path when it comes to immune health. Much of this comes down to the fabric of who we are – including our genetic inheritance – but that’s not to say that we can’t work with what we’ve got.

So, what helps, and what doesn’t? Here are 10 things you should know.

• Daniel M. Davis is head of Life Sciences and professor of immunology at Imperial College London. His latest book, Immune Health: A Myth-busting Guide (Vintage, £12), is out now.

1. There is no question that vitamin C is important to health for many reasons, but the idea that a high dose of vitamin C helps stop a cold has little merit. This idea has had a stranglehold on the popular imagination for over 50 years thanks to Linus Pauling, a double Nobel Prize-winning scientist. Without Pauling’s public advocacy and headstrong attitude, we would not think of vitamin C as we do today. He cherry-picked data to make his argument, and a lesson here is to be wary of any one person’s opinion, even if they are a well-known person who won two Nobel prizes.

2. Gut microbes do affect immune health. There’s also good evidence that probiotics can impact a person’s microbiome. But it is extremely hard to test whether probiotics really help protect us against disease. Research here is fast-moving. In the future, we will learn to harness the microbiome effectively, and understanding it has become a huge enterprise for big data science. Eventually, whole classes of microbiome medicines will arise, but we’re not there yet. Importantly, we don’t really know yet what makes up a “healthy” microbiome. One recent idea is that competition between different bacterial species in the gut may be important. A microbiome with lots of competing species may keep it balanced.

3. Keeping to a healthy weight is important for many reasons. A graph comparing our risk of infections with body weight is U-shaped. The bottoming out of the U shows a so-called “normal” weight is associated with the lowest infection risk. Being either underweight or overweight increases it.

4. Immune cells directly reside within body fat, and this is one reason why obesity can increase inflammation in the body. Fat tissue also produces lots of molecules which affect the immune system. Some experiments show that in a lab dish, an excessive level of fat molecules makes immune cells worse at killing cancer cells.

5. The effects of exercise on immune health are complicated and depend on the level of exertion. There are different, even opposing, short- and long-term consequences. Moderate exercise seems beneficial: immune cell numbers increase in number in the blood after exercise. Extreme levels of exercise may weaken immune health in the short term but can be beneficial later in life.

6. There is abundant evidence that stress affects immune health. As part of preparing the body for action, stress hormones shut down or quieten body systems not immediately needed. Stress increases blood levels of the hormone cortisol, which tends to dampen immune responses. Stress is part of life and not entirely avoidable but managing or limiting chronic long-term stress is important for immune health. A positive attitude can also help. If people have a positive mindset about stress before doing a stressful activity like public speaking, including understanding how it could enhance their performance, cortisol levels spike less. People who instinctively tend to be optimistic spike less cortisol in stressful situations.

7. Sleep and your immune health are deeply connected. A good night’s sleep helps immune health, and vice versa: good immune health helps us sleep well. Much more needs to be understood about each person’s individual need for sleep.

8. Immune health and mental health are linked. Inflammation and blood cytokine levels seem to directly affect the human brain. If mental health issues arise from an overactive immune system, as in some cases of comorbid depression, and possibly other cases too, some specific types of anti-inflammatory medicines (i.e. prescribed medicines which are more precise than ibuprofen or paracetamol) may help.

9. There is no question that ageing impacts immune health in many ways, partly because the body has already spent decades battling germs and accumulated aged cells which take on new characteristics. A low-level background inflammation seems to be a key problem. We may soon be able to formulate some specific treatments and medicines for the elderly.

10. New science about our immune system is leading to all sorts of new medicines. Take so-called immune cell therapies, which involve using immune cells, including modified versions of a patient’s own immune cells to fight disease. One example is CAR T-cell therapy which involves isolating a patient’s own immune cells and genetically modifying them to target a person’s cancer. This is already used in the treatment of some children with acute lymphoblastic leukaemia. Soon, this type of therapy will be tested for completely different diseases, including autoimmunity.

We are at the beginning of a revolutionary time for understanding the immune system, knowing how to stay healthy, and developing new immune medicines. This is a frontier of science whose time has come.