Whether or not you get sick after exposure to a pathogen comes down to two things: viral load—the amount of virus that enters your body—and how quickly your immune system can mount a response.
That response time and the strength behind it depend largely on your nutritional status. Simply put, your immune system can’t respond effectively if it doesn’t have the raw materials to do so.
Plus, immunity isn’t a switch that turns on when you get sick. It’s an active, ongoing system that either works well or doesn’t. But with the right approach, you can ensure your immune system is ready to defend your body and health. Often, it all starts long before you notice any cold or flu symptoms.
What is the immune system?
The immune system is an intricate network of dozens of cell types, signaling molecules, and organ systems that work in constant coordination. And like every biological system in the body, it depends on adequate nutrient availability to function properly.
There are two arms of the immune system, innate immunity and adaptive immunity, each playing a distinct but complementary role.
Innate immunity
Innate immunity is your first line of defense. It responds within minutes to hours of encountering a threat, making no distinction between specific pathogens; its job is essentially to contain damage fast.
This branch includes physical barriers such as the skin and mucous membranes, as well as immune cells such as neutrophils, macrophages, and natural killer (NK) cells that identify and destroy foreign invaders.
The innate system also triggers inflammation—the familiar redness, swelling, and fever that signal an immune response is underway.
Adaptive immunity
Where innate immunity is fast and broad, adaptive immunity is slow and precise. This branch takes days to fully activate. But when it does, it targets specific pathogens with remarkable accuracy.
T-cells coordinate the response and directly attack infected cells. Meanwhile, B-cells produce antibodies that neutralize pathogens and mark them for destruction.
Most importantly, the adaptive immune system has memory. Once it encounters a pathogen, it retains the blueprint to respond faster and more powerfully the next time it encounters that pathogen. This is the basis of vaccine efficacy and also why nutritional deficiencies that impair T- and B-cell function can slow and weaken your immune response when you need it most.
How to improve your immunity
Generic immune advice—sleep more, reduce stress, eat vegetables—isn’t wrong, but it is incomplete. In fact, two people can follow the same lifestyle recommendations and have vastly different immune outcomes. This is likely due to their underlying nutrient status and differing starting points.
Yet, this is also where biomarker testing can be invaluable. By measuring upstream markers, you can identify exactly where your immune system is falling short before symptoms emerge. Two of the most impactful and commonly deficient nutrients driving immune dysfunction are vitamin C and methylfolate.
Vitamin C
Vitamin C is often reduced to its reputation as a cold remedy, but its role in immune function is actually so much more than this. Immune cells actively concentrate vitamin C within their interiors to levels up to 50 times higher than in circulating plasma.
On the innate immunity side, vitamin C stimulates neutrophil production and function (the most abundant white blood cells). It supports their ability to migrate toward infection sites and enhances phagocytosis, the process by which immune cells engulf and destroy pathogens. It also protects these cells from the oxidative damage that occurs during an aggressive immune response.
Within the adaptive immune system, vitamin C promotes T-cell differentiation and proliferation, helping the body mount a targeted, lasting response to specific threats.
In fact, vitamin C deficiency can impair multiple immune functions, but adequate supplementation has been shown to reduce the duration and severity of the common cold.
Despite its importance, many people miss out on this key nutrient in their diet. On top of this, chronic stress, smoking, and alcohol may accelerate depletion.
And the truth is that standard blood panels rarely include plasma ascorbate testing, meaning deficiency often goes undetected until immune function is already compromised. However, targeted testing can help you get to the bottom of this and makes it possible to correct deficiency before it costs you or your immune resilience.
Methylfolate
Folate, also known as vitamin B9, is best known for its role in pregnancy, but its influence on immune function is significant and frequently overlooked. More specifically, methylfolate is the bioactive form that the body can use directly, without any conversion necessary.
Interestingly, a common genetic variant in the MTHFR gene, present in about 40% of the population, impairs the conversion of folic acid (the synthetic form found in most supplements and fortified foods) into its active methylfolate form. For these individuals, adequate folic acid intake on paper may not translate into adequate cellular function.
Yet, why does this matter for immunity? Folate is essential for DNA synthesis and rapid cell division, processes that are central to immune function. When the body mounts an immune response, T cells and B cells must proliferate quickly and in large numbers. Without sufficient folate, this proliferation is impaired, slowing and weakening the adaptive immune response precisely when it's needed most.
Methylfolate also supports methylation, the biochemical process that regulates immune gene expression and modulates inflammatory signaling. Research has linked low folate status to reduced natural killer cell activity and impaired antibody production. These two deficits may leave both innate and adaptive branches compromised.
Fortunately, biomarker testing for serum folate alongside homocysteine, a sensitive marker of methylation status, can reveal whether folate metabolism is functioning optimally or falling short. Elevated homocysteine, in particular, often signals that methylation is impaired even when folate levels appear normal on standard tests.
Other ways to support your immunity
Ultimately, immune resilience is built across multiple pillars. A few additional habits that meaningfully support immune function year-round include:
- Getting 7-9 hours of sleep each night
- Managing chronic stress through movement, breathwork, or mindfulness practices
- Exercising regularly (even moderate activity supports immune cell circulation)
- Maintaining a diverse, fiber-rich diet to support gut microbiome health
- Limiting alcohol (which depletes key immune-supporting nutrients)
- Taking into account your zinc status (which is another commonly deficient nutrient tied to immune cell development)
Build immune resilience that lasts
Strong immunity is the result of a system functioning at its full capacity. And when it comes down to it, vitamin C and methylfolate are two of the most evidence-backed and commonly deficient nutrients that drive immune dysfunction. But knowing whether you’re deficient—and by how much—requires more than guesswork. It requires data.
At Welle, our comprehensive testing panels measure the biomarkers that reveal how your immune system is actually performing. By doing so, we can help identify your gaps and work toward building personalized protocols designed to close them. At the end of the day, immune resilience comes down to maintaining consistent healthy habits, including specific lifestyle and dietary choices. It’s possible to make getting sick the exception, not the rule.
Sources
- Tsukagoshi, H., Shinoda, D., Saito, M., Okayama, K., Sada, M., Kimura, H., & Saruki, N. (2021). Relationships between Viral Load and the Clinical Course of COVID-19. Viruses, 13(2), 304. https://doi.org/10.3390/v13020304
- Institute for Quality and Efficiency in Health Care (IQWiG). (2023, June 6). In brief: How does the immune system work? InformedHealth.org - NCBI Bookshelf. https://www.ncbi.nlm.nih.gov/books/NBK279364/
- Carr, A. C., & Maggini, S. (2017). Vitamin C and Immune Function. Nutrients, 9(11), 1211. https://doi.org/10.3390/nu9111211
- Hemilä, H., & Chalker, E. (2023). Vitamin C reduces the severity of common colds: a meta-analysis. BMC public health, 23(1), 2468. https://doi.org/10.1186/s12889-023-17229-8
- Carboni L. (2022). Active Folate Versus Folic Acid: The Role of 5-MTHF (Methylfolate) in Human Health. Integrative medicine (Encinitas, Calif.), 21(3), 36–41.
- Kim, Y. I., Hayek, M., Mason, J. B., & Meydani, S. N. (2002). Severe folate deficiency impairs natural killer cell-mediated cytotoxicity in rats. The Journal of nutrition, 132(6), 1361–1367. https://doi.org/10.1093/jn/132.6.1361
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