As we and our beloved pets age, we often notice a gradual decline in energy, mobility, and overall resilience. What's less visible but equally significant is the aging of our immune system, a process known as immunosenescence (Nikolich-Žugich, 2018). At the heart of this change are specialized white blood cells called Natural Killer (NK) cells, the silent but powerful sentinels of our innate immune system (Vivier et al., 2008). They play a crucial role in protecting us from infections and diseases, but their function can change with age, both in humans and our furry companions (López-Soto et al., 2015).
What are Natural Killer (NK) Cells?
Imagine your immune system as a highly trained security force. While some cells, like T-cells and B-cells, require specific "identification" to recognize a threat, NK cells are like the elite, on-the-spot responders (Vivier et al., 2008). They don’t need prior exposure to a pathogen to act (Vivier et al., 2008). NK cells are a type of cytotoxic lymphocyte, meaning they can directly kill other cells, such as those infected with viruses or those that have become cancerous (Bonilla, 2017). They patrol the body, constantly scanning for abnormal cells and neutralizing them before they can cause harm (Bonilla, 2017). Their ability to respond rapidly and non-specifically makes them a critical first line of defense (Vivier et al., 2008).
The Age-Related Decline in NK Cell Activity
As humans and pets age, a phenomenon known as "NK cell senescence" occurs (López-Soto et al., 2015). While the total number of NK cells may remain stable or even increase in the elderly, their function and "killer instinct" can significantly decrease (López-Soto et al., 2015). This is a critical distinction—quantity doesn't always equal quality.
In aging adults, NK cells often show reduced cytotoxicity, meaning they are less effective at killing target cells (López-Soto et al., 2015). They may also produce fewer cytokines, which are signaling molecules that help coordinate the immune response (López-Soto et al., 2015). Research has linked this decline to a variety of factors, including chronic inflammation, a hallmark of aging, and changes in the bone marrow where these cells are produced (López-Soto et al., 2015).
Similarly, studies in veterinary immunology have shown a comparable pattern in aging dogs and cats (Segal, 2019). Older pets often have a reduced ability to mount a robust NK cell response to viral infections, making them more susceptible to illnesses (Segal, 2019). This is a key reason why vaccinations might be less effective in senior animals and why they are more vulnerable to opportunistic infections (Segal, 2019).
Health Implications of Reduced NK Cell Function
The weakening of the NK cell surveillance system in aging adults has significant health consequences. A compromised NK cell response is associated with an increased risk of severe infections, as the body’s first line of defense is not as potent (Bonilla, 2017). For example, a weakened NK cell response has been observed in older adults with more severe outcomes from viral illnesses (López-Soto et al., 2015).
Perhaps most notably, NK cells play a vital role in immune surveillance—the body's ability to detect and destroy nascent cancer cells (Shimasaki et al., 2020). The age-related decline in NK cell activity is one of the factors contributing to the higher incidence of cancer in older populations, as the immune system is less capable of identifying and eliminating malignant cells in their early stages (Shimasaki et al., 2020).
For pets, the implications are similar. A decline in NK cell function can leave senior dogs and cats more susceptible to recurring infections and certain types of tumors, highlighting the importance of preventative care and monitoring in their golden years (Segal, 2019).
Evidence-Based Strategies to Support NK Cell Activity
While the aging process is inevitable, scientific research has identified several promising, evidence-based strategies that may help support and enhance NK cell activity in both humans and animals. It is essential to note that these are supportive measures. Always consult with a healthcare professional or a veterinarian before starting any new regimen.
Exercise: Regular physical activity is one of the most powerful tools for maintaining immune health. Moderate-intensity exercise has been shown to increase the number and activity of NK cells in the bloodstream, particularly in older adults (Dimitrov et al., 2017). The effects are often transient, so consistency is key (Walsh et al., 2011). For pets, daily walks, playtime, and mental stimulation can help maintain mobility and immune function.
Nutrition: A balanced diet rich in specific nutrients can support NK cell function.
Polysaccharides: Certain complex carbohydrates, such as those found in medicinal mushrooms like shiitake and maitake, have been studied for their potential to enhance NK cell activity (Akramiene et al., 2007). The Agaricus blazei Murill (ABM) mushroom, for example, is rich in beta-glucans, a type of polysaccharide known for its immune-supporting properties (Akramiene et al., 2007). Studies suggest that ABM extract can stimulate immune cells and support the immune system (Mizuno et al., 1999).
Vitamins and Minerals: Micronutrients like Vitamin D, zinc, and selenium are essential for overall immune function and have been linked to NK cell health (Abedin & Naser, 2018; Ibs-Triebel et al., 2011; Hoffmann & Berry, 2008).
Flavonoids: These plant compounds, abundant in fruits and vegetables, have demonstrated immunomodulatory effects, including the potential to enhance NK cell activity (Panche et al., 2016).
For pets, a high-quality, balanced diet formulated for senior animals is crucial. Some pet supplements containing mushroom extracts or specific vitamins and minerals are available, but their efficacy should be discussed with a veterinarian (Segal, 2019). The Agaricus Bio Super Liquid for Pets is made with USA-grown certified organic ABM and contains beta-glucans to help maintain and enhance a pet's immune system.
Stress Management: Chronic stress can significantly weaken the immune system, particularly by suppressing the activity of Natural Killer (NK) cells (Dhabhar, 2014). This reduction in immune defense becomes even more critical as we age.
For older adults, incorporating daily stress-reducing practices—such as mindfulness meditation, laughter with loved ones, or engaging in fulfilling hobbies—can provide meaningful support for immune health (Morishima et al., 2019).
Similarly, for senior pets, maintaining a calm and consistent environment plays a crucial role in reducing stress levels. A predictable routine and a nurturing atmosphere can help support their emotional well-being and contribute to a more resilient immune system.
Probiotics and Fermented Foods: The gut microbiome plays a significant role in modulating the immune system (Wong et al., 2021). A healthy balance of gut bacteria has been shown to influence the activity of immune cells, including NK cells (Wong et al., 2021). Supplementing with probiotics or consuming fermented foods may support gut health, which in turn supports immune function (Wong et al., 2021).
For American consumers, a wide variety of fermented foods is readily available in grocery stores and health food markets. These include:
Yogurt and Kefir: These fermented dairy products are excellent sources of probiotics. Look for labels that say "live and active cultures."
Sauerkraut and Kimchi: These fermented cabbage dishes are not only rich in probiotics but also provide vitamins and fiber.
- Kimchi Cooking Tips: When stir-frying kimchi, the heat can kill the live probiotic bacteria it contains (Desjardins & Roy, 2011). Probiotic cultures generally start to die off at temperatures of 120°F (49°C) and above (Desjardins & Roy, 2011).
While cooking kimchi may kill the beneficial bacteria, it doesn't mean the food is without all benefits. Some research suggests that "heat-killed" probiotics, also known as "postbiotics," can still offer health benefits, including support for gut and immune health (O'Toole et al., 2017). However, these dead bacteria will not be able to colonize (grow and replicate in) the gut.
If your goal is to get the probiotic benefits from kimchi, it is recommended to eat it raw, either on its own as a side dish or added to cooked food after it has been removed from the heat. For example, when making kimchi fried rice, you can fry the rice and other ingredients first, then stir in cold kimchi just before serving.
Kombucha: A fermented tea drink that contains live bacteria and yeasts, making it a popular choice for gut health.
Miso: A traditional Japanese seasoning made from fermented soybeans, often used in soups and dressings.
Tempeh: A fermented soybean product that serves as a good source of protein and probiotics.
Consider Specific Supplements
In addition to a healthy lifestyle, certain supplements have been researched for their potential to support NK cell activity.
Agaricus Bio Products (for humans and pets):
These supplements, made from the Agaricus blazei Murill (ABM) mushroom, are rich in beta-glucans and polysaccharides, compounds that are involved in supporting the immune system (Mizuno et al., 1999). Agaricus Bio is available in capsule and liquid tincture forms, with the liquid form designed for quick and efficient absorption. The product for pets is formulated with USA-grown, human-grade organic ABM, aiming to maintain optimal cellular health and strengthen a pet's immune defenses. The ABM mushroom has been shown to support the production of interleukins and interferons, as well as the activity of NK cells and macrophage cells (Mizuno et al., 1999).
Cognitive Rescue:
While primarily designed to support cognitive health with Lion's Mane mushroom, this supplement also contains ingredients that may support a strong immune system. It contains a blend of dual-extracted Lion's Mane, a plant-based B vitamin complex, and BioPerine® black pepper extract for enhanced absorption. The Lion's Mane in the formula is said to contain beta-glucans and polysaccharides (Friedman, 2015).
Mushroom Ekismate:
This product contains various mushroom polysaccharides from six different mushrooms: Agaricus blazei Murill, Shiitake, Maitake, Reishi, Turkey Tail, and Cordyceps. Research on these individual mushroom ingredients indicates:
· Shiitake mushrooms contain polysaccharides that have been studied for their potential to support NK cell activity (Akramiene et al., 2007).
· Maitake mushroom extracts, particularly the D-Fraction, have been reported to support the activation of macrophages, T cells, and natural killer (NK) cells, thereby supporting immune system function (Mizuno et al., 1999; Kodama et al., 2003).
· Reishi mushrooms contain compounds, including beta-glucans, that have been shown to support NK cell count and cytotoxicity, as well as stimulate antibody production and broader immune cell populations (Consensus, 2025; Chang et al., 2014).
· Turkey Tail mushroom extracts, specifically polysaccharide-K (PSK) and polysaccharopeptide (PSP), possess immunomodulatory properties and have been shown to support peripheral blood NK cells (Alzheimer's Drug Discovery Foundation, 2019).
· Cordyceps mushrooms have been reported to significantly support NK cell activity and improve the expression of certain markers on lymphocytes (Khan et al., 2010).
Conclusion
NK cells are essential to our innate immune defense, acting as a crucial surveillance system against infections and diseases (Bonilla, 2017). While their activity may decline with age in both humans and pets, this process is not without recourse. By adopting a holistic approach that includes regular exercise, a nutrient-rich diet, stress management, and, where appropriate, targeted supplements, we can support the function of these vital immune cells. These strategies can help promote a more resilient immune system, enabling both us and our aging companions to live healthier, more vibrant lives. It is always recommended to consult with a qualified healthcare provider or veterinarian for personalized advice before starting any new supplement regimen.
References
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