Prolonged strenuous exercise is immunosuppressive and this may account for the increased incidence of upper respiratory tract infection following endurance events (Nieman, 1997). Regular consumption of a 6 % (w/v) carbohydrate (CHO) beverage during prolonged exercise has been shown to attenuate the rise in stress hormones and the fall in lymphocyte proliferation (Nieman & Pedersen, 2000) compared with ingestion of the same volume of a placebo drink. Exercise may induce temporary immunosuppression via an inhibition of T-lymphocyte intracellular cytokine production (Starkie et al. 2001). However, it is not clear if CHO ingestion can prevent the fall in T-cell interferon (IFN)-λ and interleukin (IL)-2 production during prolonged exercise. Therefore, we examined the effects of feeding beverages containing different amounts of CHO (glucose and glucose polymers) during prolonged cycling on T-cell intracellular cytokine production.

Following approval by the South Birmingham Local Research Ethics Committee, seven healthy endurance-trained men (age 25 ± 1 years, body mass 77 ± 1 kg, maximal oxygen uptake (×{special}O_2max) 4.56 ± 0.06 l min^-1; means ± S.E.M.) completed three trials consisting of cycling exercise at a work rate equivalent to 65 % ×{special}O_2max for 2.5 h in temperate ambient conditions (~25°C, ~50 % relative humidity). In random order, subjects consumed beverages containing 0, 6.4 or 12.8 % w/v CHO. The volume of drinks consumed was 500 ml just before exercise and 200 ml every 20 min during exercise. The trials took place in the morning after an overnight fast and were spaced 1-2 weeks apart. Venous blood samples were collected at pre-exercise, immediately post-exercise and at 2 h post-exercise. Following stimulation with phorbol 12-myristate 13-acetate and ionomycin, samples were stained for T-lymphocyte surface antigens (CD3, CD4 and CD8), and intracellular IFN-λ, IL-2 and IL-4 and analysed using flow cytometry. A two-way (trial X time) repeated measures ANOVA was used to compare means with post hoc Tukey or paired t tests as appropriate.

At 2 h post-exercise on the 0 % CHO (placebo) trial the number of circulating IFN-λ+ T-(CD3+) cells was significantly lower than at pre-exercise (0.15 ± 0.03 vs. 0.29 ± 0.04 X 10⁹ cells l^-1, respectively; P < 0.05) and the amounts of IFN-λ and IL-2 (but not IL-4) produced per T-cell (both CD4+ and CD8+ cells) were decreased (P < 0.05) compared with rest (Table 1). With CHO supplementation (both 6.4 and 12.8 % CHO drinks) the number of circulating IFN-λ+ T-cells, and the amount of IFN-λ, IL-2 and IL-4 produced per T-cell were unchanged from rest (Table 1).

These results indicate that the regular ingestion of 6.4 % or 12.8 % CHO drinks during prolonged exercise prevents the fall in T-cell IFN-λ and IL-2 production and that this may be the mechanism for the previously observed attenuation of exercise-induced immunosuppresion by CHO supplementation.