How does exercise impact the immune system?

Exercise and the Immune System: Beneficial Effects and Mechanisms

Regular moderate-intensity exercise enhances immune function, while prolonged high-intensity exercise may temporarily alter immune responses. 1

Impact of Exercise on Immune Function

Acute Exercise Effects

• Intensity-dependent responses:

  • Moderate-intensity exercise (up to 45 minutes) promotes beneficial immune responses 2
  • Prolonged high-intensity exercise can cause temporary alterations in immune parameters that last 3-24 hours post-exercise 3
  • These alterations include changes in:
    • T-cell function
    • NK-cell activity
    • Neutrophil respiratory burst
    • Lymphocyte proliferation
    • Cytokine balance 1, 3

• Redistribution of immune cells:

  • Exercise triggers a striking leukocytosis (increase in white blood cells) 2
  • Immune cells redistribute between blood and peripheral tissues 4
  • This redistribution is mediated by:
    • Increased hemodynamics
    • Release of catecholamines and glucocorticoids
    • Activation of the sympathetic nervous system 2

Chronic Exercise Benefits

• Regular moderate exercise:

  • Improves peripheral immune homeostasis 1
  • Reduces inflammation 2
  • Maintains thymic mass (important for T-cell development) 2
  • Enhances immunosurveillance 2
  • May limit or delay immune system aging 4

• Tissue-specific immune changes:

  • Exercise can lead to favorable tissue-specific changes in regulatory T-cell (Treg) count and function 1
  • These changes contribute to reduced inflammation in various tissues including:
    • Lungs
    • Muscle
    • Intestinal mucosa
    • Kidneys 1

The "Open Window" Hypothesis Debunked

The traditional view that vigorous exercise temporarily suppresses immunity (the "open window" hypothesis) has been challenged by recent research:

• Limited reliable evidence exists to support claims that vigorous exercise increases infection risk 4
• Post-exercise reductions in lymphocyte numbers reflect redistribution to peripheral tissues rather than suppression 4
• This redistribution actually represents a heightened state of immune surveillance 4

Exercise Recommendations for Immune Health

• Optimal exercise for immune function:

  • Regular moderate-intensity exercise (55-75% VO₂ max) 3
  • Sessions lasting up to 45 minutes 2
  • Consistent training schedule rather than sporadic intense sessions 1

• Cautions with excessive exercise:

  • Prolonged bouts (>1.5 hours) of strenuous exercise may cause temporary immune alterations 3
  • Periods of intensified training (overreaching) lasting over a week may result in longer-lasting immune changes 3
  • These changes are most pronounced when exercise is:
    • Continuous
    • Prolonged
    • Moderate to high intensity
    • Performed without food intake 3

Special Considerations

• Low-intensity exercise:

  • Walking and yoga do not appear harmful to immune function 5
  • May help relieve stress, which itself benefits immune function 5
  • However, evidence that low-intensity exercise directly enhances cell-mediated immunity remains insufficient 5

• Elite athletes:

  • Not clinically immune deficient despite rigorous training 3
  • Infection susceptibility has multifactorial underpinnings beyond just exercise 6
  • Other factors include anxiety, sleep disruption, travel, nutritional deficits, and environmental extremes 6

Clinical Applications

• Exercise can be used to enhance vaccine responses in at-risk populations 2
• Regular moderate exercise is particularly beneficial for:
  • Older adults
  • People with chronic diseases
  • Individuals with obesity
  • Patients living with cancer or chronic viral infections 2

Regular moderate exercise should be viewed as an "immune-enhancing" behavior rather than a potential cause of immune suppression, with significant benefits for long-term health and disease prevention.