Immune Responses to Strenuous Exercise and Carbohydrate Intake in Boys and Men

Abstract

Few studies describe immune responses to exercise in children, compared with adults, and none have investigated the influence of carbohydrate (CHO) intake. We hypothesized less perturbation and a faster recovery of the immune system with exercise in children, regardless of supplemental energy. Twelve boys (9.8 Ϯ 0.1 y) and 10 men (22.1 Ϯ 0.5 y) cycled for 60 min at 70% V O 2max while drinking 6% CHO (CHO-T) or flavored water (FW-T). Blood samples were collected before (PRE), immediately after (POST), and 60 min after (REC) exercise. Boys, compared with men, had smaller (p Ͻ 0.05) increases in total leukocytes (28% versus 38%), natural killer (NK) cells (78% versus 236%), and NK T cells (42% versus 128%) at POST, averaged across beverage trials. Exercise did not increase tumor necrosis factor-␣ (TNF-␣), but significantly (p Ͻ 0.05) increased IL-6 in men (189%), but not in boys (11%). In both trials, lymphocytes and T cells at REC were suppressed (p Ͻ 0.05), relative to PRE, in men (Ϫ21%), but not in boys (4%).IL-6 remained elevated ( pϽ 0.001) in men at REC, with no change from POST in boys. In boys, but not in men, CHO significantly (p Ͻ 0.05) attenuated increases in neutrophil, lymphocyte, and NK cell counts at POST. Neutrophils at REC in CHO-T were lower (p Ͻ 0.05) than in FW-T in men ‫)%52ف(‬ and in boys ‫.)%71ف(‬ CHO had no effect on TNF-␣ or IL-6 in either group. Our results indicate a distinct pattern of the immune response to exercise and CHO intake in boys, compared with men. Strenuous exercise can significantly influence several elements of the human immune system. The magnitude and direction of changes in immune cell counts, for example, are mediated by the intensity of the activity (1, 2), the nutritional status of the subject (3, 4), and changes in stress hormones, in particular epinephrine during exercise (5) and cortisol after exercise (6). Although most immune cells increase in concentration during exercise, a brief period of immunosuppression, termed the "open window," occurs during recovery from strenuous exercise and may increase susceptibility to infection (7). Another component of the immune system response to exercise is cytokines. Cytokines serve in a network to help regulate signaling of innate and specific immune responses (8). Traditionally, cytokine responses to exercise, in particular IL-6 and TNF-␣, have been interpreted in the context of immunemediated host defense (9). However, exercise-induced increases in plasma levels of IL-6 and TNF-␣ are not always associated with simultaneous increases in their intracellular production or excretion from immune cells (10 -13). Therefore, changes in these low-molecular-weight proteins with exercise likely serve roles in addition to their control of inflammation.It is important to note, however, that our current understanding of exercise-induced changes in components of the human immune system is derived primarily from adults, and there is a paucity of data on children. With respect to immune cell counts, a few studies have reported similar respo...

Correspondence

“…To the Editor: We appreciate the interest of Dr. Cunnane and Dr. Likhodii in our recent paper (1). Their letter, which raises a number of excellent points, allows us to make some additional comments about the ketogenic diet and correct one error in our paper.…”

“…To the Editor: We would like to thank Cooper and colleagues for their letter regarding our recent article (1). In their letter, Cooper and colleagues raised a concern regarding our method of measuring plasma interleukin-6 (IL-6) and the sensitivity of the chosen assay.…”

Evidence of sex-based differences in natural killer cell responses to exercise and carbohydrate intake in children

“…A resting, pre-exercise blood sample was drawn following an additional 10 min of supine rest. Subjects then consumed a small breakfast with their first drink (12 ml/kg body mass) to standardize pre-exercise nutrition, as in our previous studies (Timmons et al 2004(Timmons et al , 2006b. Volumes of 4 ml/kg body mass were subsequently consumed at 15-min intervals throughout exercise and at 20 min into recovery.…”

“…Hemoglobin and hematocrit were also assessed in these samples to calculate changes in blood and plasma volume as described (Timmons et al 2004), with all cell counts Eur J Appl Physiol (2007) 101:233-240 235 corrected for exercise-induced changes in blood volume. EDTA-treated whole blood was used to determine NK cell subsets by two-and three-color immunophenotyping as previously described (Timmons et al 2006c).…”

“…Although NK cells present in the peripheral circulation represent a small proportion of the body's total NK cell pool at rest (Westermann and Pabst 1992), the striking exercise-induced increase in the peripheral pool is thought to translate into enhanced immune surveillance, while a post-exercise reduction in blood NK cells is proposed to increase one's susceptibility to infection (Pedersen and Ullum 1994). It is therefore interesting that the magnitude of the NK cell response to exercise is smaller in children than in adults, with little evidence of post-exercise suppression in children (Timmons et al 2004). Furthermore, pubertal status influences the redistribution of NK cells during and following exercise in healthy boys and girls insofar as less mature versus more mature children experience smaller changes in NK cells (Timmons et al 2006c).…”