As a cyclist, getting sick is bad news. You feel rubbish, can’t train and lose fitness.
The better news is that cyclists tend to have better immunity than non-cyclists.
But as we’re all aware, that’s not to say riding a bike bestows you with a bulletproof immune system.
In this article, we’ll suggest ways to stay healthy while cycling.
With help from three immunology experts, a WorldTour nutritionist and an elite gravel racer, we’ll also delve into the complex relationship between exercise and immunity.
How does exercise affect your immune system?
What is the immune system?
Before we go any further, what exactly is the immune system and immunity?
Dr John Campbell, senior lecturer at the University of Bath’s department of health, describes the immune system as “a system of organs, tissues and cells that…protect us from external agents, such as viruses and bacteria, but also things within us that go wrong, like cancer”.
He says immunity is an “umbrella term for the protection that we have against agents that might cause us harm”.
Some aspects of immunity are simple, such as the way the skin forms a protective barrier against pathogens.
But Dr Campbell adds: “Immunity can also be extremely complex.”
For example, our immune response to a Covid vaccine is “very specific and involves very complex interplay between very specific cells”.
Due to the immune system’s complexity, Dr Campbell says “nobody fully understands what's going on”.
This has led to misconceptions about exercise and immunity, which we’ll get on to later.
How does exercise strengthen your immune system?
One of the benefits of cycling is that, like other forms of aerobic exercise, it enhances your immunity.
Increased heart rate as you exercise boosts the circulation of infection-busting white blood cells, leading to better “immune surveillance”.
Dr Campbell says: “Cells that have been resting somewhere in the body, in response to increased heart rate, are pushed into the bloodstream to conduct the early stages of immune surveillance.
“After exercise is finished, these cells go off into different tissues to see if there's anything untoward there that the immune system should respond to.
“That is one of the potential mechanisms through which exercise might prevent and also treat cancers.”
Increased life expectancy
Cycling also reduces your risk of developing other chronic health issues.
Professor Neil Walsh, an expert in immunology, nutrition and exercise science from Liverpool John Moores University, says: “Exercise brings about an anti-inflammatory environment which helps reduce your risk of diseases like diabetes and heart disease.”
Improved life expectancy of cyclists is possibly linked to them having better immunity for longer. “Regular exercise like cycling is absolutely fantastic for longevity,” says Walsh.
Dr Campbell adds: “There is definitely evidence there that if you're a regular cyclist, I don’t know if it's enhanced immune health, but perhaps you’ll have better maintained immune health, as you get into older age.”
A 2018 study of masters cyclists at the University of Birmingham found their immune systems were stronger than healthy non-cyclists at the same age.
The reason remains unclear, but Dr Campbell believes it could be because cycling through the decades helps retain muscle mass, maintaining the immune system.
Less stress, fewer infections
Stress is bad for immunity because it increases the body’s levels of cortisol, which suppresses the immune system.
So if cycling reduces stress, it could stop you from getting ill so often.
Professor Walsh says: “For most people who are regular exercisers, their exercise is a form of destressing.
“If you get enjoyment from something, it has very positive effects on mental health.
“And in turn, that's good for the immune system.”
Can exercise worsen immunity?
Today, the consensus is that endurance exercise, such as cycling, doesn’t impair your immune system.
Professor Walsh says: “The research for many years thought that heavy exercise could zap the immune system by bringing about an excessive anti-inflammatory effect where you get increases in hormones like the stress hormone cortisol.
“But what we've learned is that athletes who train hard are rarely clinically immune compromised.”
In addition, researchers noticed lower levels of white blood cells in the blood after exercise. They concluded this would lead to more infections.
“But actually these cells are actually just going off into other tissues to look for pathogens,” says Dr Campbell.
“We're increasingly thinking that this immunosurveillance response is, of course, a good thing.”
Studies of marathon runners in the 1980s showed heightened incidence of upper respiratory infections in the weeks following an event compared to control groups.
However, subsequent research couldn’t find a mechanism by which the exercise itself led to illness.
Dr Campbell says: “It's probably just people getting together at mass participation events and spreading germs that increases the incidence of these particular infection symptoms rather than the immune system being suppressed by exercise.”
Professor Walsh says there’s no evidence even Tour de France cyclists, who are pushing their bodies to the limits for three weeks, have suppressed immune systems.
Lauren De Crescenzo, the 2021 women’s Unbound winner, believes cycling brings overall benefit to her health. But she admits elite gravel racing tests her immunity.
“The intensity of my training and racing does push my body to its limits. I feel I’m existing on a ledge and my goal is never to tip over,” she says.
Risks of under-fuelling for your immunity
Although not a direct consequence of exercise, inadequate carbohydrate intake is believed to be bad for immunity.
Will Girling, a nutritionist at the EF Education Easy-Post WorldTour team, says: “Performing exercise while in a low-glycogen and low-carbohydrate state will increase the cortisol response to that session, which in turn will suppress your immune system, potentially weakening your ability to combat infection.”
Longer-term under-fuelling is also linked to immune suppression, particularly if it causes Relative Energy Deficiency in Sport (RED-S).
Dr Campbell says: “One line of thinking is if you aren't compensating your energy expenditure through exercise with appropriate calorie intake of the right stuff, then you might start to have deficiencies in different systems in the body and the immune system might eventually become suppressed.”
But he says the effect of RED-S on the immune system requires more research.
Why immunity is important for cyclists
Despite being healthier and less infection-prone than the average person, cyclists should still care about their immunity.
Professor Walsh says you shouldn't ride with a respiratory infection. Although resting is the right thing to do, it means you lose out on training time.
He adds: “If you ride when you've got a respiratory infection, not only is your training very poor quality but you could get more sick.
“So infections are a real problem for riders and they should do all they can to stop getting sick.”
Don’t worry about getting ill
Catching colds and bugs is inevitable and Professor Walsh says getting sick two to three times a year is normal.
Nonetheless, succumbing to infection more often might not be a cause for concern if your circumstances, such as having children of nursery age, expose you to lots of bugs, according to Dr Campbell.
If you are concerned about your immunity though, he suggests speaking to your doctor. They may recommend blood tests to check for abnormalities, such as nutrient deficiencies.
How to stay well while cycling
Hygiene, stress, sleep and nutrition are the key things to consider to avoid infection while training for cycling.
Hygiene
Basic hygiene measures remain effective ways to prevent infection.
Professor Walsh says: “Avoiding sick people sounds stupid but it's super important, as is washing your hands and not translocating bugs [through touch] into your nose, your eyes and your mouth.”
When you are ill, Professor Walsh says sneezing into your elbow, not over people, and potentially isolating yourself will help prevent transmission.
Minimising exposure to ill people can seem harder than during the pandemic, which is something De Crescenzo acknowledges.
“Travelling for races exposes me to a lot of germs. That’s why I still wear a mask on aeroplanes – or as I like to call them ‘Petri dishes’,” she says.
While travelling, she also carries hand sanitiser and Beekeeper’s Propolis throat spray, which she believes provides defence against airborne diseases.
Dr Campbell also emphasises the effectiveness of face masks. He advises paying extra attention to hygiene at mass-participation events where hundreds of people may be sharing the same toilets.
Stress
Stress is bad for immunity because it increases cortisol levels.
So minimising stress could reduce your risk of succumbing to illness.
While many cyclists like training with power and tracking wellness metrics on their smartwatches, they're often less good at accounting for what the psychologist Dr Bruce McEwen called “allostasis” – the wear and tear of everyday life on our mental and physical health.
“It's what happens when they're not on Zwift and not on the bike that more often than not dictates whether they get sick or not,” says Professor Walsh.
Sleep
The impact of sleep is similar to that of stress on immunity.
Professor Walsh says prolonged periods of short or disturbed sleep disturb the “stress hormonal axis”, which includes cortisol and catecholamines such as adrenaline.
When someone’s stress axis becomes dysregulated, they are more prone to infection, he explains.
“Army recruits who sleep six hours or less a night are four times more likely to get a respiratory infection than those army recruits who sleep more than six hours,” he says.
“And general population studies show that individuals who sleep less than seven hours seem to get more respiratory infections.”
Both quantity and quality of sleep are important, according to Professor Mike Gleeson, emeritus professor of exercise biochemistry at Loughborough University.
He says: “In one study, people whose sleep efficiency was rated 98 per cent – very good – were five times less likely to develop symptoms as people whose sleep efficiency was less than 92 per cent.”
This means someone who falls asleep quickly could need fewer hours in bed than someone who takes longer to nod off.
Signs you’re getting enough sleep of sufficient quality include feeling invigorated when you wake up, according to Professor Walsh.
On the other hand, daytime sleepiness indicates you need more or better kip.
Professor Walsh doesn’t advocate tracking your sleep in minute detail, but says your sleep rhythm is a “good barometer” of your stress level.
“If you've got social stress, relationship stress, you're racing too much or you've not got enough rest in your training program then your sleep might start to change.
“That's when it [sleep tracking] is really useful,” he says.
Nutrition
Balanced diet
There’s no nutritional golden bullet that will defeat all infections.
Professors Gleeson and Walsh, and Dr Campbell, say a balanced diet without a nutrient deficiency or a large, long-term calorie deficit will help to keep you healthy.
This is because macronutrients aid immune cell metabolism and protein synthesis; micronutrients support antioxidant defence; and glucose, amino acids and fatty acids help fuel your immune system.
Professor Gleeson says: “Eat lots of fresh vegetables and fruit. These contain polyphenols and flavonoids, which help your immune system.
“Make sure your plate looks colourful, with tomatoes, peppers, carrots or squash and leafy greens.
“You can eat a large volume without worrying about calories but they will keep you healthy.”
Macronutrients
De Crescenzo underscores the importance of carbohydrates during demanding training blocks.
“In addition to lots of sleep, they both improve my recovery metrics and keep the watts flowing,” she says.
Aside from carbohydrates, protein is a crucial macronutrient for your immune system.
Professor Walsh says: “It's the protein intake that the immune cells really rely on.”
He recommends 1.2 to 1.6 grams of protein per kilo of body weight a day, up to double the recommended intake for a non-cyclist.
Supplements
During the winter, a lack of sunlight exposure causes the amount of vitamin D in our bodies to drop to levels that suppress our immune system.
Therefore, Professor Walsh advises taking a daily supplement containing 400 international units (IU) or 10 micrograms of vitamin D. Alternatively, you could consume the same amount from vitamin D-reinforced foods, such as some dairy products (it's difficult to get 400 IU of vitamin D from food alone).
A well-balanced diet is unlikely to be deficient in vitamin C, however, given that the recommended intake of 60mg a day is easy to achieve.
Nonetheless, when you start to get ill, Professor Walsh recommends increasing your intake of “tolerogenic” supplements such as vitamin C, vitamin D, prebiotics (contained in high-fibre foods such as oats) and probiotics (found in some yoghurts).
He says: “They are really helpful because they dampen inflammation and almost limit the chances of an overly exuberant immune response.
"This limits how sick you get."
Zinc lozenges are recommended too because zinc is an antiviral agent believed to stop the common cold virus from docking with cells.
Professor Gleeson says: “It has been shown that these can actually reduce your duration of illness by a third, or three days.”
When De Crescenzo gets a scratchy throat, she takes a supplement called Pillar Performance Ultra Immune C. This contains 1,000mg of vitamin C and 15mg of zinc.
Such a high dose of vitamin C may even help prevent infection in the first place, according to Professor Walsh.
But being anti-inflammatory, he says vitamin C could also limit your body’s adaptation to training stimulus, which makes you fitter.
Training progression
Progressively increasing your training load by following a structured training plan and periodising your training can reduce your risk of illness, according to Professor Walsh.
For example, he says you shouldn’t increase the volume and intensity by more than five to 10 per cent per week.
He also recommends doing more regular, shorter training sessions rather than fewer longer ones, and planning an easier recovery week after every second or third week.
Should you cycle if you’re ill?
The 'below the neck' rule applies to cycling with a cold.
This means you’re probably fine to ride with a runny nose or light cough, as long as you decrease the intensity and duration, according to Dr Campbell.
In fact, De Crescenzo finds a gentle ride can relieve snuffly symptoms.
But symptoms below the neck, such as a tight chest and muscle aches, are signs of a more serious 'systemic infection’.
Professor Walsh says: “There are lots of clinical implications, meaning it's very unwise to exercise hard with below-the-neck symptoms.
“If you exercise hard when you've got a systemic infection that can cause the virus to spread to the heart and you can end up with higher risk of heat injury, which can occur in cold as well as hot conditions."
Professor Walsh believes the guidance against riding while ill needs to be strengthened.
“People who are coughing their guts up, looking green and producing nasal discharge, which is disgusting in a bunch anyway, shouldn't be out, quite frankly,” he says.
Regardless of how she feels, De Crescenzo says she will rest if she has tested positive for Covid-19.
How to return to training after illness
It’s best to wait until two days have passed without any below-the-neck symptoms before resuming light exercise.
Bearing in mind the effects of detraining, you should build up to the level you were at pre-infection over a few weeks, according to Professor Walsh.
He says you should return to cycling from Covid-19 just as you would from any other viral infection – that’s to say, slowly and steadily.
De Crescenzo says she successfully followed this approach after catching Covid at the end of the 2023 season.
After taking time off the bike, she says: “Resuming training involved a gradual reintroduction to cycling. I even went running a few times.
“I tried prioritising my overall well-being, giving my body time to fully recover from Covid-19 and a long season of pushing my body to its max.”
Dr Campbell also advises a cautious return to training, noting that viruses can linger for a surprisingly long time – coronavirus lateral flow tests often produce positive results days after symptoms dissipate.
He adds: “See how your body reacts through medium- and high-intensity work and low- and medium-intensity, long rides.
“You should also be conscious that you will have probably lost some muscle mass in that time.
“It can happen really quickly, especially if you've been bed-bound with an infection, and can cause imbalances.
“That's something that you should also consider upon returning to sport.”
