Immunosenescence: How Aging Affects Your Immune System and What May Help
Last reviewed: March 21, 2026, 7:02 a.m.
Immunosenescence refers to the gradual decline in immune function that occurs as a natural part of the aging process, and it is one of the primary reasons older adults are more susceptible to infections, respond less robustly to vaccinations, and experience higher rates of serious complications from illnesses like influenza and pneumonia. The thymus gland, which is responsible for producing and maturing T cells, begins to shrink after puberty and is substantially reduced in size and function by age 50, leading to a decreased output of naive T cells capable of responding to new pathogens. Simultaneously, the accumulated memory T cells that remain become less diverse and may become functionally exhausted, a state characterized by reduced proliferative capacity and impaired cytokine production. Understanding these changes is the first step toward exploring strategies that may help support immune resilience in older age.
Beyond T cell changes, immunosenescence involves alterations across nearly every branch of the immune system. Natural killer cell numbers may actually increase with age, but their per-cell cytotoxic activity tends to decline, potentially reducing the body's ability to eliminate virus-infected cells and early cancer cells. Macrophages and neutrophils in older adults often show reduced phagocytic efficiency, diminished production of reactive oxygen species for pathogen killing, and impaired chemotaxis — the ability to migrate toward sites of infection. B cell diversity also declines, leading to a reduced antibody repertoire and weaker responses to new antigens, which is a key reason why vaccines are often less effective in elderly populations. Additionally, aging is associated with a chronic low-grade inflammatory state sometimes called inflammaging, characterized by elevated baseline levels of pro-inflammatory cytokines that may paradoxically impair rather than enhance protective immune responses.
Research has identified several nutrients that may play a role in supporting immune function during aging. Vitamin D deficiency is particularly common in older adults due to reduced skin synthesis, decreased outdoor activity, and lower dietary intake, and multiple observational studies have linked low vitamin D levels with increased susceptibility to respiratory infections in this population. Zinc deficiency is another concern in the elderly, as serum zinc levels tend to decline with age, and zinc is critical for T cell development and function — some clinical trials suggest that zinc supplementation in older adults with low zinc status may help improve certain markers of immune function and reduce the incidence of infections. Medicinal mushrooms such as reishi (Ganoderma lucidum) contain polysaccharides called beta-glucans that have demonstrated immunomodulatory properties in preclinical research, and preliminary human studies suggest they may support natural killer cell activity, though larger clinical trials are needed to confirm these findings in aging populations.
Astragalus (Astragalus membranaceus) is a traditional Chinese medicinal herb that has attracted research attention for its potential immunomodulatory and anti-aging properties. Preclinical studies have shown that astragalus polysaccharides may enhance macrophage activity, promote T cell proliferation, and support the production of immunoglobulins. Some researchers have been particularly interested in astragaloside IV, a compound in astragalus that has been studied for its potential effects on telomerase activity, though human clinical evidence for these effects remains limited. While these nutritional strategies show promise, it is important to emphasize that no supplement can reverse immunosenescence, and the most evidence-based approaches to healthy aging include maintaining a nutrient-dense diet, engaging in regular moderate exercise, ensuring adequate sleep, managing stress, and staying current with recommended vaccinations.
Beyond T cell changes, immunosenescence involves alterations across nearly every branch of the immune system. Natural killer cell numbers may actually increase with age, but their per-cell cytotoxic activity tends to decline, potentially reducing the body's ability to eliminate virus-infected cells and early cancer cells. Macrophages and neutrophils in older adults often show reduced phagocytic efficiency, diminished production of reactive oxygen species for pathogen killing, and impaired chemotaxis — the ability to migrate toward sites of infection. B cell diversity also declines, leading to a reduced antibody repertoire and weaker responses to new antigens, which is a key reason why vaccines are often less effective in elderly populations. Additionally, aging is associated with a chronic low-grade inflammatory state sometimes called inflammaging, characterized by elevated baseline levels of pro-inflammatory cytokines that may paradoxically impair rather than enhance protective immune responses.
Research has identified several nutrients that may play a role in supporting immune function during aging. Vitamin D deficiency is particularly common in older adults due to reduced skin synthesis, decreased outdoor activity, and lower dietary intake, and multiple observational studies have linked low vitamin D levels with increased susceptibility to respiratory infections in this population. Zinc deficiency is another concern in the elderly, as serum zinc levels tend to decline with age, and zinc is critical for T cell development and function — some clinical trials suggest that zinc supplementation in older adults with low zinc status may help improve certain markers of immune function and reduce the incidence of infections. Medicinal mushrooms such as reishi (Ganoderma lucidum) contain polysaccharides called beta-glucans that have demonstrated immunomodulatory properties in preclinical research, and preliminary human studies suggest they may support natural killer cell activity, though larger clinical trials are needed to confirm these findings in aging populations.
Astragalus (Astragalus membranaceus) is a traditional Chinese medicinal herb that has attracted research attention for its potential immunomodulatory and anti-aging properties. Preclinical studies have shown that astragalus polysaccharides may enhance macrophage activity, promote T cell proliferation, and support the production of immunoglobulins. Some researchers have been particularly interested in astragaloside IV, a compound in astragalus that has been studied for its potential effects on telomerase activity, though human clinical evidence for these effects remains limited. While these nutritional strategies show promise, it is important to emphasize that no supplement can reverse immunosenescence, and the most evidence-based approaches to healthy aging include maintaining a nutrient-dense diet, engaging in regular moderate exercise, ensuring adequate sleep, managing stress, and staying current with recommended vaccinations.