Experts debunk myths around immune boosting, revealing what actually helps protect against infections

In a world obsessed with “immune-boosting” tricks, from cold plunges to vitamin megadoses, many wonder if they can truly supercharge their body’s defences. But are these methods actually effective, or just expensive fads? BBC Radio 4’s Inside Health investigates.

Cold Water Swimming: A Game-Changer or a Gimmick?

Braving near-freezing temperatures, journalist James Gallagher took the plunge into a 3.9°C reservoir, hoping to test whether icy swims could strengthen his immune system. While studies suggest cold exposure triggers a temporary flood of white blood cells—the body’s infection fighters—experts remain sceptical.

“Within a few hours, everything returns to normal,” explains immunologist Prof Eleanor Riley. “There’s no proof that cold-water swimmers catch fewer colds or infections.”

Exercise: The Real Immune Booster?

While icy plunges may not offer lasting protection, regular moderate exercise could. Studies suggest that active individuals experience fewer viral infections.

“There isn’t conclusive proof, but all the evidence points towards exercise helping immunity,” says Dr Margaret McCartney of the University of St Andrews. One study even found that 80-year-old cyclists had immune systems resembling those of much younger people.

Vitamins: Miracle Cure or Marketing Scam?

Vitamin C is often hailed as a must-have for fighting colds, but experts disagree.

“It’s a no from me,” Dr McCartney states bluntly. “Unless you’re deficient, extra vitamin C won’t make a difference.”

Multivitamins? Also a waste for most, she says, dismissing them as “expensive urine.”

However, vitamin D, which drops in winter due to lack of sunlight, remains a grey area. Some research suggests it could help those with respiratory conditions, but there’s no solid proof that it benefits everyone.

Gut Health and Immunity: Are Probiotics the Answer?

Interest in probiotics—good bacteria that supposedly enhance immunity—is skyrocketing. While gut health plays a crucial role in overall wellbeing, Dr McCartney warns that real-world data remains lacking.

“We need more evidence before recommending prebiotics or probiotics for immune support,” she cautions.

Does the Time of Day Affect Your Immune System?

Surprisingly, when you’re exposed to germs could impact your risk of getting sick.

“The immune system is strongest in the early morning and weakens later in the day,” says Prof Riley. “You may have better protection if you’re vaccinated or exposed to a virus in the morning.”

What Actually Weakens Your Immune System?

While boosting immunity may be difficult, people do damage their defences in predictable ways:

• Smoking destroys the lungs’ protective barriers, allowing infections in more easily.
• Obesity fuels chronic inflammation, making the body more vulnerable.
• Chronic stress elevates cortisol, which suppresses immune function.

Reducing stress, quitting smoking, and maintaining a healthy weight are some of the most effective ways to protect your immune system.

The Verdict: Can You ‘Boost’ Immunity?

If you already eat well, exercise, and don’t smoke, your immune system is likely in peak condition.

“Can you push it beyond normal? No,” says Prof Riley.

Instead of wasting money on immune-boosting gimmicks, experts recommend vaccination, good hygiene, and smart lifestyle choices as the best defences against illness.