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How to Support Your Immune System Before Winter

written by

The OneVit Team

The OneVit Team

Updated on

10th April 2026

reading time

7 min

How to Support Your Immune System Before Winter

Every autumn, the same pattern repeats: the days shorten, temperatures drop, people spend more time indoors in closer proximity, and cold and flu season begins. Rather than waiting for the first sniffle, the smarter approach is to invest in your immune system ahead of the seasonal challenge.

This guide explains how the immune system actually works, why winter presents specific challenges, and which nutrients have the strongest evidence for supporting immune resilience. We deliberately avoid the word "boost," because the immune system is not a dial you turn up. It is a complex, multi-layered defence network that works best when properly resourced and balanced.

How the Immune System Works

The immune system operates in two main layers. The innate immune system is the first line of defence: physical barriers (skin, mucous membranes), antimicrobial proteins and rapid-response cells like neutrophils and macrophages that attack anything recognised as foreign. It responds within minutes to hours and does not require prior exposure to a specific pathogen.

The adaptive immune system is slower but more targeted. It relies on T cells and B cells that learn to recognise specific pathogens, mount a tailored response, and retain a memory of that encounter for faster future defence. Vaccination works by priming this adaptive response without causing disease1.

Both layers require adequate nutritional support to function properly. Key nutrients act as cofactors for immune cell production, proliferation and communication. When those nutrients are depleted, the immune response is compromised at every level.

Why Winter Is Harder on Immunity

Several factors converge during the UK winter to increase infection risk.

Reduced vitamin D synthesis. Between October and March, the sun sits too low in the sky for UVB radiation to trigger vitamin D production in the skin at UK latitudes. Since vitamin D is critical for immune cell activation, this seasonal shortfall can affect immune readiness2.

Increased indoor crowding. Cold weather drives people indoors, increasing close contact and the transmission of respiratory viruses. Dry indoor heating further compromises the mucous membranes that serve as physical barriers to infection.

Cold-induced immune suppression. Breathing cold, dry air can impair the innate immune defences of the upper respiratory tract, reducing the efficiency of the mucociliary clearance system that physically removes inhaled pathogens3.

Behavioural changes. Shorter days, less sunlight and colder temperatures often lead to reduced physical activity, poorer sleep quality and higher consumption of comfort foods low in nutritional density. These factors compound the direct physiological challenges.

Vitamin D: The UK's Most Important Immune Nutrient

Vitamin D is not just a bone nutrient. It plays a direct role in both innate and adaptive immunity. Vitamin D receptors are present on virtually all immune cells, and the active form of vitamin D (calcitriol) modulates the function of macrophages, dendritic cells and T cells2.

Low vitamin D status has been associated with increased susceptibility to respiratory tract infections in multiple observational studies. A large meta-analysis of individual participant data from 25 randomised controlled trials found that daily or weekly vitamin D supplementation reduced the risk of acute respiratory tract infection, with the greatest benefit seen in those with the lowest baseline vitamin D levels4.

In the UK, the Scientific Advisory Committee on Nutrition recommends 10µg (400 IU) daily for everyone over five during autumn and winter, and year-round for those with limited sun exposure5. NDNS data shows that a significant proportion of UK adults fall below the 25 nmol/L deficiency threshold during winter months, with estimates varying from around a fifth to over a third depending on age group and survey period6.

OneVit Vitamin D3 & K2 provides cholecalciferol (D3) alongside vitamin K2 for normal calcium metabolism. Taking it with a meal containing dietary fat enhances absorption.

Vitamin C: Supporting the Front Line

Vitamin C supports immune function through multiple mechanisms. It contributes to the normal function of neutrophils and lymphocytes, supports the physical barrier function of the skin, and acts as a potent antioxidant that protects immune cells from oxidative damage generated during the inflammatory response7.

The evidence for vitamin C in preventing colds in the general population is modest, but it becomes more significant in people under physical stress. A Cochrane review found that regular vitamin C supplementation reduced cold duration by 8% in adults and 14% in children, with more pronounced effects in those exposed to short periods of severe physical stress (such as marathon runners), where the incidence of colds was halved8.

Vitamin C is water-soluble and rapidly excreted, which means consistent daily intake matters more than occasional high doses. OneVit Vitamin C provides daily antioxidant and immune support.

Zinc: The Immune Gatekeeper

Zinc is required for the normal development and function of immune cells including neutrophils, natural killer cells and T cells. It also plays a role in the integrity of skin and mucosal membranes, the body's first physical barriers against infection9.

Zinc deficiency, even at marginal levels, impairs immune function. A meta-analysis found that zinc supplementation reduced the duration of the common cold by approximately 33% when taken within 24 hours of symptom onset, though the evidence is primarily from studies using zinc lozenges or syrup rather than oral capsules10.

Zinc is included in OneVit Complete Multivitamin and OneVit Testosterone Support Complex, both of which provide meaningful zinc doses as part of broader formulations.

Probiotics and Gut-Immune Health

A significant proportion of immune activity is coordinated through the gut, concentrated in the gut-associated lymphoid tissue (GALT)11. The gut microbiome trains and modulates immune responses, making it a critical factor in overall immune resilience.

Probiotic supplementation has been studied for its effects on respiratory tract infections, with several meta-analyses finding modest but consistent reductions in the incidence and duration of upper respiratory infections12. The effects are strain-dependent, with Lactobacillus and Bifidobacterium species showing the most consistent benefits.

OneVit Probiotics Complex provides 19 billion live cultures from seven bacterial strains, combined with the prebiotic inulin, to support a diverse and well-functioning gut microbiome.

Mushroom Supplements: Beta-Glucans and Immune Modulation

Medicinal mushrooms including reishi, shiitake, maitake and turkey tail contain bioactive compounds called beta-glucans, which are polysaccharides that modulate immune function by activating macrophages and natural killer cells13. Unlike immunostimulants (which simply ramp up the immune response), beta-glucans appear to act as immunomodulators, supporting a balanced and appropriate immune response.

OneVit Mushroom Complex combines five mushroom species (including reishi and lion's mane) with zinc and vitamin D, creating a multi-layered formula designed to support normal immune function.

Building an Immune Support Routine

The foundation (year-round): OneVit Vitamin D3 & K2 and OneVit Complete Multivitamin address the most common UK-specific nutritional gaps that compromise immune readiness.

The seasonal layer (October to March): Add OneVit Vitamin C for daily antioxidant and immune support. Add OneVit Probiotics Complex if not already taking it, to support the gut-immune connection.

The advanced layer (for those seeking comprehensive support): OneVit Mushroom Complex provides beta-glucan-rich immune modulation alongside the established immune benefits of vitamin D and zinc.

Start building this routine in September or October, before the seasonal challenge is in full swing. The goal is to enter winter with optimised nutrient stores, not to scramble once illness has already arrived.

The Bottom Line

You cannot supplement your way out of poor sleep, chronic stress, a sedentary lifestyle or a diet built on processed food. But when the foundations are in place, targeted supplementation provides the immune system with the specific nutrients it needs to support normal immune function during the most demanding time of year.

Vitamin D is non-negotiable in the UK. Vitamin C, zinc and probiotics provide additional, evidence-backed support. Mushroom supplements offer an emerging layer of immune modulation. Layer them in based on your individual needs, and start early enough for the benefits to accumulate before they are needed most.

Disclaimer: This article is for informational purposes only and is not intended to replace professional medical advice. Supplements support normal immune function but do not prevent, treat or cure any disease.

References

  1. Chaplin DD. Overview of the immune response. J Allergy Clin Immunol. 2010;125(2 Suppl 2):S3-23. PMC

  2. Aranow C. Vitamin D and the immune system. J Investig Med. 2011;59(6):881-886. PMC

  3. Eccles R. An explanation for the seasonality of acute upper respiratory tract viral infections. Acta Otolaryngol. 2002;122(2):183-191. PubMed

  4. Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017;356:i6583. PMC

  5. Scientific Advisory Committee on Nutrition (SACN). Vitamin D and Health. 2016. GOV.UK

  6. Office for Health Improvement and Disparities. National Diet and Nutrition Survey 2019 to 2023: Report. 2025. GOV.UK

  7. Carr AC, Maggini S. Vitamin C and Immune Function. Nutrients. 2017;9(11):1211. MDPI

  8. Hemilä H, Chalker E. Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev. 2013;(1):CD000980. PubMed

  9. Wessels I, Maywald M, Rink L. Zinc as a Gatekeeper of Immune Function. Nutrients. 2017;9(12):1286. MDPI

  10. Science M, Johnstone J, Roth DE, Guyatt G, Loeb M. Zinc for the treatment of the common cold: a systematic review and meta-analysis of randomized controlled trials. CMAJ. 2012;184(10):E551-E561. PMC

  11. Wiertsema SP, van Bergenhenegouwen J, Garssen J, Knippels LMJ. The Interplay between the Gut Microbiome and the Immune System. Nutrients. 2021;13(3):886. MDPI

  12. Hao Q, Dong BR, Wu T. Probiotics for preventing acute upper respiratory tract infections. Cochrane Database Syst Rev. 2015;(2):CD006895. PubMed

  13. Akramiene D, Kondrotas A, Didziapetriene J, Kevelaitis E. Effects of beta-glucans on the immune system. Medicina (Kaunas). 2007;43(8):597-606. PubMed

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