Immunity: Avoiding the ills and chills this winter

That system can become overloaded when we are exposed to too many pathogens at once, or when the body is under stress. Winter is a particularly challenging time for the immune system: cold and flu viruses circulate more widely, people spend more time indoors in closer proximity to one another, and the season often coincides with reduced daylight hours and additional lifestyle stress.

While there is no sure way to prevent every attack on the immune system, it is worth being aware of the seasonal pressure and taking practical steps to support your body's own defences, in conjunction with a healthy diet and lifestyle. Here are our top tips for supporting immunity this season.

Your microbiome is the collection of microbes, bacteria, archaea, fungi, and viruses, that live on and in your body. These microbes play many vital roles in your health, including helping digest food, produce certain vitamins, and support your body's natural defences. Your microbiome is unique to you and changes over time depending on factors such as diet, exercise, age, and antibiotic exposure.

The composition of your microbiome may also affect how well your body copes with the cold and flu season. One study found that people with a more diverse microbiome were less likely to catch a cold after exposure to rhinovirus, the virus responsible for the common cold. The study authors speculated that the microbes in a diverse microbiome may help train the immune system to recognise potential pathogens.

A diet that lacks essential nutrients can impair immune function and increase susceptibility to illness. Conversely, a diet built around a wide variety of nutrient-rich foods can help support immune function. Research has linked full-spectrum diets to healthier levels of immunoglobulins (Woof & Kerr, 2006), proteins that play a key role in immunity, and to higher antioxidant status, which helps protect cells from oxidative damage.

Several key nutrients play a supporting role in immune function:

• Vitamin A: important for the development of immune cells.
• Vitamin C: helps protect immune cells from oxidative damage.
• Selenium: an essential trace element that helps protect cells from oxidative stress.
• Vitamin E: helps protect cells from damage caused by free radicals.
• Zinc: involved in producing cytokines, the signalling molecules that help regulate immune activity.
• Iron: essential for normal immune cell function.

These nutrients need to be consumed in the right amounts to be effective. Too much or too little of any one nutrient can work against you, so aim for a varied diet rich in these foods, supplementing where your intake genuinely falls short, in conjunction with a healthy diet and lifestyle.

When we sleep, our bodies produce cytokines, proteins that help regulate the immune system and support recovery from illness or injury by promoting tissue repair. Sleep also helps regulate production of white blood cells, the body's primary line of defence against infection.

In one study, people who slept fewer than six hours per night were four times more likely to catch a cold than those who slept more than seven hours (Besedovsky & Born, 2015). A single night of poor sleep has been shown to reduce immune cell production, underscoring how important consistent, quality sleep is for a well-functioning immune system.

Small, consistent changes to your sleep habits, a wind-down routine, a consistent bedtime, limiting screens before bed, can meaningfully improve sleep quality and, in turn, support immune function, in conjunction with a healthy diet and lifestyle.

Regular exercise may be one of the best ways to support immune function. Physical activity affects immunity through several mechanisms: it can increase the diversity of gut microbiota (Bermon et al., 2015), it triggers release of immunomodulatory molecules such as cytokines and chemokines, and it affects the nervous system in ways that support immune cell production.

Research has also linked regular resistance training to fewer reported upper respiratory tract infections, greater immunoglobulin A levels (an antibody that plays a role in mucosal defence), and improved sleep quality (Kovacevic et al., 2018), which itself supports immune function. While it is tempting to stay rugged up at home on the coldest days, getting out and training may be one of your best defences against those winter chills, in conjunction with a healthy diet and lifestyle.

Proper hydration is essential for overall health, and it plays a specific role in supporting a strong immune system. The human body is roughly 60% water, and every system depends on it to function correctly. Water transports nutrients and oxygen to cells, helps regulate body temperature, and supports cognitive function and cellular repair.

Even mild dehydration has been shown to reduce white blood cell count and contribute to fatigue, both of which make it harder for the body to mount an effective response to illness. Drinking plenty of fluids, especially when you are unwell or trying to stay ahead of a bug going around, gives your immune system the support it needs.

Amino acids are the building blocks of protein and play a role in many biological processes. Among the 20 amino acids, three branched-chain amino acids (BCAAs), leucine, isoleucine, and valine, are of particular interest for immune function. BCAAs are essential nutrients, meaning the body cannot produce them and they must come from the diet.

Research suggests BCAA intake may support immune function through several mechanisms, including supplying the raw materials immune cells need for protein synthesis, helping manage inflammation, and potentially supporting immune cell activity directly. BCAAs are found naturally in foods such as meat, fish, and eggs; supplementation offers a more concentrated and convenient way to help meet your needs, particularly around training.

Winter puts real, predictable pressure on your immune system, but the fundamentals stack the odds back in your favour: a diverse, well-fed microbiome, a full-spectrum diet, consistent quality sleep, regular movement, proper hydration, and adequate amino acid intake. Supplements can help fill genuine gaps, but they work best layered on top of these basics, in conjunction with a healthy diet and lifestyle.

• Woof, J.M. and Kerr, M.A. (2006). The function of immunoglobulin A in immunity. J. Pathol., 208: 270-282. https://doi.org/10.1002/path.1877
• Bermon, S., Petriz, B., Kajeniene, A., Prestes, J., Castell, L., & Franco, O. L. (2015). The microbiota: an exercise immunology perspective. Exerc Immunol Rev, 21(21), 70-79.
• Besedovsky, L., & Born, J. (2015). Sleep, Don't Sneeze: Longer Sleep Reduces the Risk of Catching a Cold. Sleep, 38(9), 1341-1342.
• Kovacevic, A., Mavros, Y., Heisz, J. J., & Singh, M. A. F. (2018). The effect of resistance exercise on sleep: A systematic review of randomized controlled trials. Sleep medicine reviews, 39, 52-68.