The compelling link between physical activity and the body's defense system

Abstract

This review summarizes research discoveries within 4 areas of exercise immunology that have received the most attention from investigators: (1) acute and chronic effects of exercise on the immune system, (2) clinical benefits of the exercise-immune relationship, (3) nutritional influences on the immune response to exercise, and (4) the effect of exercise on immunosenescence. These scientific discoveries can be organized into distinctive time periods: 1900-1979, which focused on exercise-induced changes in basic immune cell counts and function; 1980-1989, during which seminal papers were published with evidence that heavy exertion was associated with transient immune dysfunction, elevated inflammatory biomarkers, and increased risk of upper respiratory tract infections; 1990-2009, when additional focus areas were added to the field of exercise immunology including the interactive effect of nutrition, effects on the aging immune system, and inflammatory cytokines; and 2010 to the present, when technological advances in mass spectrometry allowed system biology approaches (i.e., metabolomics, proteomics, lipidomics, and microbiome characterization) to be applied to exercise immunology studies. The future of exercise immunology will take advantage of these technologies to provide new insights on the interactions between exercise, nutrition, and immune function, with application down to the personalized level. Additionally, these methodologies will improve mechanistic understanding of how exercise-induced immune perturbations reduce the risk of common chronic diseases.

Keywords: Aging; Exercise; Immunology; Infection; Inflammation; Mass Spectrometry; Nutrition.

Fig. 1

Key research areas and basic findings in exercise immunology.

Fig. 2

Exercise immunology research can be organized into 4 distinctive periods.

Fig. 3

Acute exercise stimulates the interchange of innate immune system cells and components between lymphoid tissues and the blood compartment. Although transient, a summation effect occurs over time, with improved immunosurveillance against pathogens and cancer cells and decreased systemic inflammation.

Fig. 4

The contrast in acute immune responses to heavy exertion (e.g., a marathon race) and a 30- to 45-min walking bout. DTH = delayed-type hypersensitivity; IgA = immunoglobulin A; Ne/Ly = neutrophil/lymphocyte ratio; NK = natural killer; OB = oxidative burst.

Fig. 5

J-curve model of the relationship between the exercise workload continuum and risk for upper respiratory tract infection (URTI). Other factors such as travel, pathogen exposure, sleep disruption, mental stress, and dietary patterns may influence this relationship. This figure was adapted from Nieman.

Fig. 6

The upper tertiles of fitness and exercise frequency are associated with reduced numbers of days with upper respiratory tract infections (URTI). Data from Nieman et al.

Fig. 7

C-reactive protein (CRP) and interleukin-6 (IL-6) values for obese and athletic groups (data expressed as mean ± SD). Data are from ongoing studies in the first author's lab during the past 2 decades. BMI = body mass index.

Fig. 8

Carbohydrate ingestion before and during exercise attenuates postexercise inflammation.