Building Your Body’s Fortress – A Winter Wellness Guide to Immune Health

Maintaining immune system health is important during the colder months, when cold and flu viruses are more common.  Adults often experience 2-4 colds per year¹ and so supporting your immune system is especially important during this season. Like a well-guarded fortress, your immune system relies on multiple layers of defence, and its strength can be influenced by a range of lifestyle factors. These include sleep, stress management, and nutrient intake, which we’ll explore further.

Often poor sleep and stress go hand in hand, but how do they affect our immune system? It is well documented that poor sleep or sleep deprivation reduces our immune defenses such as lowering natural killer cell activity². Think of your natural killer cells as the patrolling guards or watchmen of your fortress, checking for threats and attacking invaders quickly if they arrive. Chronic sleep disruption also increases our risk of infection, particularly upper respiratory tract infections, influenza and severe COVID-19³. So next time you are deciding whether to press ‘next episode’ on Netflix or head to bed, choose the latter. Seven to nine hours of deep, restful sleep is always advised⁴.

Stress is a common driver of many health ailments, including sleep disturbances, and when both are at play, immunity can be compromised. Ongoing, unresolved stress can cause dysregulation of the immune system, much like a fortress under chronic siege. This decreases T cells and B cells – specialised defenders who fight off specific infections and remember past invaders, further increasing susceptibility to infection⁵. Stress management is crucial for our 21^st-century living and so employing skills that are manageable yet enjoyable will have a profound impact on our immunity this winter. These may include deep breathing exercises, mindfulness, exercise, connection with loved ones, spending time in the outdoors and journalling.

Every meal we consume is a chance to fortify our immune system. Food provides us with crucial vitamins and minerals to improve our barriers and increase our defence system against lurking bacteria and viruses. While many nutrients are needed for optimal function, vitamin C, vitamin D, zinc and selenium stand out as key players on our immune systems frontline. Beyond their many functions, here are a few ways they support our fortress:

• Vitamin C: Critical for enhancing epithelial barrier function such as our skin, oral and nasal mucosa and respiratory tract⁶. Like the strong walls of a fortress, these barriers need to be strong to keep invaders out. Furthermore, vitamin C is important for enhancing the function of neutrophils and macrophages. These are our first responders that attack and clear out invaders. Consider incorporating vitamin C rich foods into your diet such as papaya, red capsicum, citrus fruit, strawberries, kiwi fruits and broccoli.
• Vitamin D: Important for stimulating the antimicrobial activities of macrophages and monocytes, our first responders, by producing a compound called cathelicidin⁷. This acts as a special weapon that takes down threats quickly. Low vitamin D levels are also associated with an increased risk of infections⁷. While fatty fish such as sardines, salmon and mackerel, fortified dairy and eggs are great dietary sources to include, the best source of vitamin D is sensible and safe exposure to UVB radiation from the sun⁸.
• Selenium: The immune system is sensitive to free radical production and oxidative stress⁹, much like the integrity of a fortress sensitive to corrosive rust. Antioxidants, like selenium, act as the maintenance crew to repair damage and strengthen defenses. Further to this, selenium’s antioxidant capacity improves the function of the breakdown of bacteria within the cell⁹, enhancing the clearance of infection more efficiently. Selenium rich foods to consider incorporating into your diet include Brazil nuts, seafood, meat and eggs.
• Zinc: An important mineral required for the normal development and function of front-line players, such as neutrophils, macrophages and natural killer cells¹⁰. Much like a key strategist, zinc disrupts viral attacks and inhibits the enemy’s ability to multiply by blocking viral replication¹⁰. Zinc is best absorbed from animal-based sources such as oysters, beef, and lamb. However, plant-based sources like pumpkin seeds, hemp seeds, cashews, and almonds also provide valuable sources of zinc.

At certain times, a strategic upgrade may be beneficial to further support your body’s natural defenses, which may include nutrients found in dietary supplements. For example, Wellmune® is a unique baker’s yeast beta-glucan shown to ‘train’ front-line immune cells to detect and respond more efficiently in the clearance of pathogens¹¹. Additionally, bovine lactoferrin, a protein found in cows’ and breast milk, has been studied for its ability to bind iron and support immune function¹². Speak with a healthcare professional to determine if these nutrients are suitable for your needs.

Supporting your immune defences this winter starts with prioritising quality sleep, stress management and nourishing the body with key nutrients. Targeted supplementation may also help support your body’s natural defences during the colder months.

References:

1. Health Direct Australia. Colds and flu. June 2024. https://www.healthdirect.gov.au/colds-and-flu (accessed Apr. 1, 2025)
2. Garbarino S et al. Role of sleep deprivation in immune-related disease risk and outcomes. Commun Biol. 2021;4:1304.
3. Jones S et al. The public health impact of poor sleep on severe COVID-19, influenza and upper respiratory infections. 2023,93:104630
4. Sleep Health Foundation. How much sleep do you really need? January 2024. https://www.sleephealthfoundation.org.au/sleep-topics/how-much-sleep-do-you-really-need. (accessed Apr. 15, 2025).
5. Alotiby, A. Immunology of Stress: A Review Article. J. Clin. Med. 2024; 13(21),6394.
6. Carr A et al. Vitamin C and Immune Function. Nutrients. 2017;9(11):1211.
7. Sirbe C et al. An Update on the Effects of Vitamin D on the Immune System and Autoimmune Diseases. 2022;3(17):9784.
8. Cancer Council. Vitamin D. https://www.cancer.org.au/cancer-information/causes-and-prevention/sun-safety/vitamin-d. (accessed May. 6 2025).
9. Puertollano M et al. Dietary antioxidants: immunity and host defense. Curr Top Med Chem. 2011;11(14):1752-66.
10. Sadeghsoltani F et al. Zinc and Respiratory Viral Infections: Important Trace Element in Anti-viral Response and Immune Regulation. Biol Trae Elem Res. 2021;200(6):2556-2571.
11. De Macro Castro E et al. β-1,3/1,6-Glucans and Immunity: State of the Art and Future Directions. Mol Nutr Food Res. 2021;65(1):e1901071
12. Giansanti, F et al. Lactoferrin from Milk: Nutraceutical and Pharmacological Properties. Pharmaceuticals (Basel). 2016;9(4):61