The Hidden Reason You Keep Getting Sick Every Winter

The overlooked science of secretory IgA, mucosal immunity and your body’s first line of defence

Every winter, the pattern feels familiar. Someone at work starts coughing, your children bring something home, the temperature drops and suddenly it feels as though everyone around you is fighting a cold, flu or respiratory infection. We tend to think about immunity as something happening deep inside the bloodstream, involving white blood cells, antibodies, vitamins and the familiar advice to “boost your immune system.” Yet pathogens trying to enter your body encounter another sophisticated defence system first.

It covers your nose, mouth, throat, respiratory tract and gastrointestinal tract. Collectively, these surfaces form part of the mucosal immune system, and one of their most important defenders is an antibody called secretory immunoglobulin A, or secretory IgA (SIgA).

Understanding this often-overlooked layer of immunity may change the way you think about supporting your body through winter.

Your Immune System Has a Front Door

Your gastrointestinal and respiratory tracts occupy an unusual position in human biology. Technically, they are inside your body, yet their surfaces are continuously exposed to the outside world. Every breath introduces environmental particles and microorganisms into your respiratory tract, while everything you eat brings the gastrointestinal tract into contact with food antigens and an extraordinary ecosystem of microorganisms.

These mucosal surfaces therefore need to perform a remarkable balancing act: tolerating harmless substances and beneficial microbes while helping prevent potentially harmful organisms from establishing themselves.

This is where secretory IgA becomes particularly important.

IgA is the predominant antibody class associated with mucosal surfaces, including the respiratory and gastrointestinal tracts. SIgA can bind microorganisms and other antigens at these surfaces, helping prevent their attachment and penetration through a process sometimes described as immune exclusion. Researchers consequently regard secretory antibodies as an important component of our first-line defence against respiratory infections.

Think of SIgA less like an army arriving once an invasion has already begun and more like security stationed at the entrance.

Modern research into influenza, RSV and SARS-CoV-2 has renewed scientific interest in mucosal immunity precisely because systemic immunity and mucosal immunity are not identical. A 2024 review highlighted the important role of SIgA in protection against respiratory viruses and the growing scientific effort to develop interventions capable of generating stronger mucosal immune responses.

That doesn’t mean depleted SIgA is the sole reason somebody repeatedly becomes ill during winter. Exposure, age, vaccination status, underlying health, nutrition, sleep, pathogen characteristics and numerous other variables influence susceptibility. What it does tell us is that healthy mucosal immunity deserves far more attention in the winter wellness conversation.

Stress, Sleep and the Immune System

One of the fascinating aspects of mucosal immunity is how closely it appears to interact with the way we live.

Deadlines, financial pressure, intense training, family responsibilities, constant notifications and inadequate recovery don’t exist separately from our biology. The nervous and immune systems continuously communicate with one another, which means psychological stress can produce measurable physiological effects.

Research examining stress and SIgA suggests that the relationship depends partly on the nature and duration of the stressor. Acute stress may temporarily increase salivary SIgA, while delayed or prolonged stress responses have been associated with reduced secretion. Research into intestinal immunity has similarly suggested that stress-mediated changes in SIgA may influence intestinal defence and integrity.

This is more nuanced than simply saying “stress lowers your immunity,” but the broader message is important: chronic stress without adequate recovery can influence immune regulation.

Sleep forms another part of that equation. The relationship between sleep and SIgA itself is complex, and experimental sleep-deprivation studies haven’t produced a simple linear relationship between fewer hours of sleep and lower IgA. What the broader scientific literature does establish much more clearly is that adequate, consistent sleep is integral to normal immune regulation.

In other words, supplements should support the foundations of health rather than attempt to compensate for their absence. Sleep isn’t optional immune maintenance.

Nutrition matters too, and zinc deserves particular attention. Zinc participates in the development and function of both innate and adaptive immune cells, while deficiency is associated with impaired immune responses and increased susceptibility to infection. Zinc also contributes to gastrointestinal integrity, making adequate nutritional status particularly relevant when considering the relationship between the gut and immune system.

The evidence is stronger for saying that zinc deficiency impairs immune function generally than claiming that zinc deficiency specifically causes SIgA depletion in otherwise healthy adults. It’s an important distinction, and one that illustrates why good immune health is rarely about one nutrient, one supplement or one pathway.

Supporting the Terrain, Not Just Fighting the Invader

Perhaps the most useful way to think about winter immunity is to move away from the idea of waiting until something goes wrong and then trying to “fight” it.

A more holistic approach is to support the biological terrain your immune system depends upon throughout the season: adequate sleep, sufficient protein and micronutrients, regular movement, stress management, gut health and appropriate preventative healthcare.

Certain nutritional compounds are also attracting scientific interest for their potential roles in different aspects of immune and mucosal function. Three particularly fascinating examples are bovine colostrum, propolis and Chaga mushroom.

Colostrum: Nature’s First Immune Food

Before mammals consume ordinary food, they receive something extraordinarily specialised: colostrum.

Produced immediately after birth, colostrum contains proteins, immunoglobulins, growth factors and numerous other biologically active compounds designed to provide concentrated nourishment during an exceptionally vulnerable stage of life. Its remarkable composition has naturally led scientists to investigate whether bovine colostrum might offer useful nutritional properties later in life.

Human research is still developing, but some findings are intriguing. Research involving physically active adults has explored bovine colostrum supplementation in relation to upper respiratory symptoms and mucosal immunity, with earlier studies also investigating changes in salivary IgA.

This doesn’t mean that colostrum prevents winter infections or automatically “restores” depleted SIgA. What it does mean is that its unique composition and emerging evidence make it particularly interesting for anyone exploring the relationship between gut integrity, mucosal health and immune resilience.

Ancestral Supplements Grassfed Colostrum brings this traditional food into a convenient modern format. Sourced from grass-fed cattle, it provides bovine colostrum with its naturally occurring proteins and bioactive components preserved through careful processing. For those interested in strengthening the nutritional foundations of gut and immune health, it represents an intriguing meeting point between ancestral nutrition and modern research.

Propolis: The Hive’s Natural Defence System

If colostrum represents one of nature’s first forms of mammalian nourishment, propolis provides an equally fascinating example from the insect world.

Honeybees create propolis by collecting plant resins and combining them with beeswax and other substances. They then use this complex material throughout the hive, where it forms part of the colony’s protective environment.

Its chemistry has attracted considerable scientific attention. Reviews of propolis research describe antibacterial, antiviral, antioxidant, anti-inflammatory and immunomodulatory activity, much of which is associated with its diverse flavonoids, phenolic acids and other compounds. A substantial proportion of this evidence comes from laboratory and preclinical research, however, and rigorous human clinical evidence for preventing or treating respiratory infections remains more limited.

That distinction is important. Calling propolis a broad-spectrum antimicrobial can describe biological activity observed in research; it should not be interpreted to mean that taking propolis has been clinically proven to prevent or treat every type of infection.

ORGAMIKA PropolisGold uses the standardised Promunel™ propolis extract, providing six characterised polyphenols and 1,220 mg of pure propolis extract per serving in a convenient liquid formulation. Positioned for immune, respiratory and oral wellness support, it is particularly relevant to this conversation because the mouth and respiratory tract themselves form part of our critical mucosal interface with the outside world.

Chaga: Ancient Forest Wisdom Meets Modern Research

Then there is Chaga (Inonotus obliquus), the distinctive fungus traditionally associated with birch forests across cold northern climates.

Chaga has a long history of traditional use, but modern researchers have become interested in the numerous bioactive compounds found within it. Laboratory and preclinical research has investigated its potential antioxidant and immunomodulatory properties, with experimental evidence suggesting that Chaga extracts can influence aspects of immune activity.

Once again, context matters. High-quality human clinical research remains limited, so Chaga shouldn’t be positioned as a proven treatment or preventative for infection. Instead, it is perhaps better understood as a traditional botanical with fascinating biological properties that modern science is beginning to investigate more closely.

ORGAMIKA Chaga Mushroom Extract Powder provides a 10x concentrated, wild-crafted Chaga extract and offers an easy way to incorporate this traditional mushroom into a contemporary wellness routine. Its antioxidant profile makes it particularly interesting as part of a broader approach to supporting immune function and resilience against oxidative stress.

It also lends itself beautifully to winter: stirred into a warm drink alongside spices such as cinnamon, cardamom or turmeric, Chaga can become less of a “supplement” and more of a daily wellness ritual.

Ancient Wisdom Meets Modern Immunology

There is an interesting thread connecting colostrum, propolis and Chaga. Colostrum comes from nature’s first mammalian food. Propolis comes from the protective chemistry of the hive. Chaga comes from centuries of traditional botanical practice.

Long before researchers could measure immunoglobulins, cytokines or immune-cell signalling, traditional cultures were already interested in foods and natural substances associated with resilience and wellbeing.

Contemporary wellness figures have helped bring some of these ideas back into popular conversation. Anthony William, for example, has been influential in popularising foods, herbs and mushrooms such as Chaga among wellness audiences, while Dr. Zach Bush has contributed to broader public discussion around the gut, environmental exposures and whole-body health.

Their perspectives should, however, be distinguished from the clinical evidence. When discussing SIgA, mucosal immunity and respiratory infection specifically, peer-reviewed immunology remains the scientific foundation.

And that science gives us a surprisingly modern reason to revisit a very old idea: health isn’t simply about fighting an invader once it gets inside. It’s also about maintaining the barriers designed to keep unwanted organisms out in the first place.

Rethinking Your Winter Immune Strategy

Perhaps the biggest mistake we make with winter immunity is waiting until our throat feels scratchy or somebody in the household gets sick before thinking about immune health.

A more intelligent approach begins much further upstream. Prioritise consistent sleep. Manage chronic stress where possible. Eat sufficient protein and micronutrient-rich whole foods. Ensure adequate zinc and other essential nutrients. Support gastrointestinal health. Move regularly. Give your body time to recover.

Then consider targeted nutritional support as part of that foundation rather than as a replacement for it.

Ancestral Supplements Grassfed Colostrum offers a fascinating whole-food approach to gut and immune nutrition. ORGAMIKA PropolisGold brings the complex protective chemistry of the hive into a standardised modern extract. ORGAMIKA Chaga Mushroom Extract Powder draws on centuries of traditional use alongside emerging research into antioxidant and immune-modulating compounds.

None is a magic shield against winter illness, and that’s precisely the point.

Your immune system isn’t a switch you suddenly turn on when you’re exposed to a pathogen. It is an extraordinary network of physical barriers, antibodies, microorganisms, immune cells and signalling molecules working quietly every minute of every day.

This winter, don’t just think about boosting immunity. Think about supporting the barriers that defend you first.

Explore the Winter Immune Edit

Ancestral Supplements Grassfed Colostrum — whole-food nutritional support for gut and immune health.

ORGAMIKA PropolisGold — standardised propolis polyphenols for immune, respiratory and oral wellness.

ORGAMIKA Chaga Mushroom Extract Powder — concentrated wild-crafted Chaga for antioxidant and immune-system support.

Supplements are not intended to diagnose, treat, cure or prevent disease. People experiencing frequent, severe or unusual infections should seek appropriate medical advice rather than assuming low secretory IgA is the cause.

References

Longet S, et al. Research on secretory IgA and mucosal immunity in respiratory viral infection. Antiviral Research. 2024.

Tsujita S, Morimoto K. Research examining secretory IgA in saliva as a marker of stress.

Campos-Rodríguez R, et al. Research on stress and intestinal secretory immunoglobulin A.

Haase H, Rink L. Research examining the relationship between zinc and immune function.

Keen CL, Gershwin ME. Research on zinc deficiency and immune function.

Brinkworth GD, et al. Research examining concentrated bovine colostrum supplementation and upper respiratory tract symptoms.

Magnavacca A, et al. Review of antiviral and immunomodulatory activities associated with propolis.

Szychowski KA, et al. Review of Inonotus obliquus (Chaga), traditional use and emerging scientific research.