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Working mother stressed that can weaken her immune system

Stress Can Increase Infection Risk

Ongoing stress triggers high levels of cortisol, which can weaken immune function.

Scientifically reviewed by Dr. Gary Gonzalez, MD, in August 2023. Written by: Michael Downey.

It’s hard to avoid stress.

The concern is that increased stress can weaken immune functions.

Ongoing stress triggers high levels of cortisol, a steroid hormone.

Excess cortisol diminishes immune functions, and has been shown to increase disease risk while shortening human lifespans.1-17

A 2019 study found that anticipating stress the next day is associated with elevated cortisol soon after waking up in the morning.18

Human studies demonstrate that specific plant extracts can reduce cortisol levels and inhibit its destructive effects.19-24

Stress Weakens Immune Function

woman and doctor

A recent poll reports that 45% of Americans feel that their mental health has been negatively impacted due to worry and stress over viral illness.25

Cortisol is one of the body’s main stress hormones.

During stressful times, the adrenal glands release it as part of the “fight-or-flight” response.26

Necessary for life-or-death situations, cortisol directs a complex series of hormonal and physiological changes that support either fleeing to safety or fighting off the threat.27,28

Cortisol boosts muscle tension, blood sugar, heartbeat, tissue-repair substances, and mental focus. At the same time, cortisol turns down non-urgent processes such as immune functions, along with the digestive and reproductive systems.29

When the stressful threat has passed, cortisol is supposed to return to normal “balanced” levels.

When stressors are almost always present cortisol remains “turned on.”

Its continuing high presence in the blood adversely affects critical functions of the body and brain.30

Danger of Elevated Cortisol

Stress results in a decrease in levels of lymphocytes. These immune cells are used to kill viruses and other invaders.31,32

Lymphocyte counts are often reduced when one is fighting a viral infection.33-35

Even if it’s just for a few days, social isolation and loneliness also weaken immunity.36

Older individuals are more susceptible to stress and to stress-induced immune damage.37

Long-term overexposure to excess cortisol disrupts almost all body processes, increasing risk for health problems that include:1-17,38

  • Immune impairment,
  • Cardiovascular disease,
  • Diabetes,
  • Osteoporosis,
  • Gastrointestinal problems,
  • Obesity,
  • Neurodegeneration, including Alzheimer’s disease, and
  • Anxiety, depression, and insomnia.

Most worrisome, chronically elevated cortisol is linked to increased mortality risk.

A large study of people over age 65 found that men with high cortisol levels were 63% more likely to die than those with lower levels.

Women with elevated cortisol were 82% more likely to die than those with low levels.5 And those with high urinary cortisol had a five-fold increased risk of death from cardiovascular disease.3

Higher cortisol is also associated with shortening of telomeres, the stretches of DNA that cap the ends of chromosomes.39,40 As telomeres shorten, the cells that bear them get closer to the ends of their lives, aging the tissues and organs in which they dwell.

It’s impossible to avoid all stress. But scientists have demonstrated that natural compounds can lower excess cortisol levels.

What you need to know

Counter the Immune-Damaging Effects of Stress

  • Stress increases levels of the hormone cortisol, which can weaken immune function.
  • A weak immune system raises the risk of infections caused by viruses and other pathogens.
  • Chronically elevated cortisol increases the risk of other diseases—including cardiovascular disease, diabetes, and neurodegeneration—and of overall mortality.
  • Human studies show that both a lychee-green tea blend and a combination of two bark extracts from Magnolia and Phellodendron trees reduce high cortisol levels.
  • These compounds can effectively reduce unwanted circulating cortisol, safely inhibiting its destructive effects.

Lychee-Green Tea Blend Lowers Cortisol

Woman with her head on desk

Grown in China since the 11th century,41 lychee fruit is rich in polyphenols that promote a variety of biological activities, most notably the ability to reduce inflammation and cortisol levels.19

Most lychee products sold today contain long-chain polyphenols, which are not easily absorbed in the intestinal tract.

To overcome this obstacle scientists developed a low molecular size extract derived from lychee fruit and green tea.42

The result is a new compound that is stable and highly absorbable.

Researchers tested this lychee-green tea blend on human monocytes, a type of immune cell. They found that it significantly suppressed inflammatory signaling molecules called cytokines, helping to decrease inflammation.43

This confirmed earlier results from clinical trials that evaluated the lychee-green tea blend’s ability to lower stress and stress-induced cortisol.

Reducing Stress-Induced Cortisol

Researchers randomly assigned 19 sedentary but healthy male volunteers (with an average age of 22) to take either a placebo or 100 mg of the lychee-green tea blend daily for four weeks.

They conducted blood tests for cortisol and other inflammatory markers before and after the study, and after exercise, which raises cortisol levels.19

Unlike those in the placebo group, the men taking the blend showed significant decreases in cortisol and the pro-inflammatory cytokines IL-1beta and IL-6. The lychee-green tea extract also reduced the rate of increase of these factors following exercise.19

In another study, 10 healthy men took either a placebo or 100 mg of the lychee-green tea blend twice daily for 10 days before exercising under low-oxygen conditions, to increase stress.20

Exercise increased cortisol substantially in the placebo group. The cortisol increase in the lychee-green tea group was significantly smaller.20

Physically Induced Cortisol

Scientists next assessed the effects of the lychee-green tea blend on cortisol and inflammation caused by physical stress.

Either a placebo or 100 mg of the blend was given to 13 healthy males. After 30 minutes, the lower portion of each man’s legs was immersed in hot water for half an hour. Researchers measured cortisol and inflammatory cytokines before and after this procedure.21

Compared to placebo subjects, lychee-green tea recipients had significantly lower concentrations of cortisol, IL-1beta, and IL-6 after the heat-related stress. These benefits continued for up to two hours after the stress ended. (IL-1beta and IL-6 are pro-inflammatory factors.)

Lychee-green tea recipients also had significantly lower increases in temperatures of the skin and body core during the application of heat, indicating a more balanced and improved response to the physically stressful event.21

Later studies confirmed that the lychee-green tea blend prevents heat-induced elevations in body temperature. This reduces fluid loss from sweating under heat stress and prevents stress-induced blunting of immune response.44-47

How to Measure Your Stress Levels

Stress can become so constant that you don’t even notice how stressed you are.

A cortisol blood test allows you to find out whether your levels are elevated and by how much. If they’re high, that’s a sign of ongoing stress.

Lifestyle changes like meditation, exercise, and eating a healthy diet can bring this level down. Regular use of safe, plant compounds also lowers elevated cortisol and can prevent the immune-weakening effects of stress.

A follow-up cortisol test will show whether your efforts have been successful or need to be intensified.

Effects of Tree Bark Extracts

Woman meditating

Scientists have identified two tree bark extracts that deliver similar protection against elevated cortisol.

The extracts come from a magnolia species, Magnolia officinalis, and Phellodendron amurense, also known as Amur cork tree.

Both have been used in traditional Chinese medicine for centuries and have been shown to have non-sedating anti-anxiety effects.22

In one study, investigators enlisted 56 healthy but moderately stressed individuals. Twice daily, participants were given either a placebo or 250 mg of a mixture containing both bark extracts.23

After four weeks, the bark extract recipients had 18% lower cortisol levels compared to placebo recipients. They also had mood improvements and reduced feelings of stress, depression, anger, and fatigue, all likely related to lowered cortisol.23

Two small, additional studies documented benefits of this bark extract blend:

  • One six-week study was conducted on healthy but overweight premenopausal women (aged 20-50) with above-average anxiety. Compared to a placebo, a 250 mg dose of the bark extract combination, given three times a day, significantly decreased anxiety.22
  • A second study was conducted on a similar group of women with above-average anxiety, who reported eating more in response to stress. The placebo group had significant weight gain over the six-week study. But weight gain was prevented in the bark extract subjects.24

Elevated cortisol weakens the immune system’s ability to fight infection. Lychee-green tea blend and the bark extract combination have been shown to reduce excessive cortisol secretion in response to stress.


Stress weakens immune functions by raising levels of cortisol.

This increases the risks of infections and chronic diseases and shortens lifespans.

A lychee-green tea blend provides highly absorbable nutrients that have been shown to lower cortisol in human studies.

A combination of two bark extracts from the Magnolia and Phellodendron trees has also been shown, in human trials, to lower cortisol and reduce outward manifestations of stress.

These compounds offer one approach to reducing excess cortisol levels, which may counteract some of the harmful effects inflicted by chronic stress.

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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