Woman sneezing into tissue from reduced immune system function

Key Nutrients to Optimize Immunity

Aging weakens the immune system, increasing vulnerability to infections. Studies show how key nutrients help maintain more youthful immune function.

By Michael Downey.

Aging weakens the immune system, increasing vulnerability to infections, including colds, flu, and upper respiratory viruses.1,2

Specific nutrients have been demonstrated to help optimize immune functionality.

Daily intake can help defend against infectious agents.

Vitamin C

The association between vitamin C and immune health may result from its ability to stimulate the production and function of white blood cells.3,4

Scientists have found that vitamin C:

  • Promotes development of T-cells and proliferation of natural killer cells in laboratory studies,5,6
  • Increases interferons, signaling molecules the body uses to trigger immune responses,4
  • Neutralizes excess free radicals caused by infections, limiting oxidative damage and illness severity, and7,8
  • Helps produce collagen, a protein that can enable skin and the linings of respiratory/digestive tracts to maintain an anti-infection barrier.7

This evidence suggests that vitamin C may help modulate and resolve inflammation, fight infections, and promote tissue healing.

A meta-analysis of 31 clinical studies showed that oral vitamin C reduces cold duration by an average of 9.4%. It may also help prevent and reduce the severity of viral respiratory tract infections.9


The plant flavonoid quercetin helps support a prompt immune response to common colds and other upper respiratory infections.10,11

It also provides defense against viral and bacterial infections:

  • Middle-aged and older adults taking quercetin daily reduced sick days taken off for colds by 31% and reduced symptom severity by 36%,11
  • In animal studies, quercetin decreased infection rate for Helicobacter pylori, the cause of many forms of ulcers and potentially, some cancers of the stomach,12,13 and
  • In salmonella-infected cells, quercetin inhibited infected cellular viability.14 Salmonella bacteria cause roughly 26,500 hospitalizations in the U.S. yearly and are especially dangerous in older adults.15

Humans can have difficulty absorbing quercetin.16 So, scientists integrated it into a phytosome, a fatty substance serving as a carrier, making it up to 50 times more bioavailable than standard quercetin.17

Vitamin D

Adequate vitamin D may help lessen the severity of infections, or possibly even prevent them, by: 18-21

  • Interfering with viruses’ ability to replicate,
  • Helping repair cellular linings, including in lung airways,
  • Boosting production of proteins that protect against infection, and
  • Inhibiting immune system production of excess pro-inflammatory compounds in the lungs.

Meta-analyses of clinical trials show that vitamin D protects against respiratory tract infections.22,23

Taking 5,000-8,000 IU of vitamin D daily and checking levels with annual blood tests can help maintain an optimal 25-hydroxyvitamin D blood level of 50-80 ng/mL.

What you need to know

Support Immune Functions

  • A strong immune system helps prevent and fight viral and bacterial infections.
  • Several nutrients can help keep the immune system working optimally.
  • These nutrients support a range of mechanisms that help maintain more youthful immunity.


Zinc has benefits throughout the body, including immune support. Deficiency is common among the elderly.1,24,25

In a study, zinc supplementation in elderly individuals boosted an experimental test of stress resilience of white blood cells. The authors of this study suggest this relationship may be important for combating immunosenescence.26

Aging adults who replenish their zinc levels may help slow immune function decline.1

Unique Probiotic Strain

Secretory IgA is an antibody that targets viruses and bacteria invading the mucosal membranes lining the nose and upper respiratory tract.

Healthy IgA activity can prevent cold and flu viruses from gaining a foothold.28

Scientists investigating probiotics identified a specific bacterial strain, Lactobacillus rhamnosus CRL1505, that significantly increased levels of secretory IgA in a preclinical model.27

L. rhamnosus CRL1505 has been shown in preclinical studies to help inhibit the pathogens that cause common colds, flu, bronchitis, and pneumonia.27,29

A trial of healthy male and female children found that, compared to placebo, consuming 100 million CFU (colony-forming units) of L. rhamnosus CRL1505 five days weekly for six months resulted in:30

  • 61% fewer cases of tonsillitis and pharyngitis (a throat infection),
  • 55% fewer cases of cold or flu,
  • 49% fewer infections,
  • 46% fewer cases of fever, and
  • 33% less need for antibiotic use.

These children were aged two to five, a group particularly susceptible to respiratory infections.30

Yeast Fermentate

S. cerevisiae fermentate is a special yeast culture extract that improves the immune response to environmental allergens and colds, as shown in controlled human studies.31-35

In one trial, volunteers took a placebo or 500 mg of S. cerevisiae fermentate daily for five weeks at the start of allergy season. Placebo users saw no change in seasonal allergies. But half of the treated men reported a complete absence of allergy symptoms, which returned within two weeks after they stopped treatment.31

Another study found those receiving the extract had significantly fewer symptoms and a shorter duration of symptoms.35

A later study found that those receiving the yeast extract had significantly less incidence of colds or flu-like symptoms, and some reduction in duration of symptoms.34

Studies suggest that S. cerevisiae fermentate works by promoting two key immunity defenses: natural killer cell activity and secretory IgA production.31,32


Immune function declines with age, increasing the risk of infection.

Taken daily, certain nutrients support healthier immune functionality.

These include vitamin C, quercetin, vitamin D, zinc, the probiotic Lactobacillus rhamnosus CRL1505, and S. cerevisiae fermentate.

If you have any questions on the scientific content of this article, please call a Life Extension Wellness Specialist at 1-866-864-3027.


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