We investigated the effects of placebo and chlorella intake on salivary SIgA secretion in the participants of a kendo training camp. Although the scores for physical well-being before the camp were slightly lower than a usual level (3.0), all of our subjects participated in nearly all of the training programs. Body mass changes and subjective physical well-being scores during the camp were comparable between the placebo and chlorella groups. Based on these results, we consider that there were no intergroup differences in the physical requirements of this training camp. However, with respect to the baseline levels, salivary SIgA secretion rates decreased only with placebo intake but not with chlorella supplementation. These changes in the salivary SIgA secretion rate were comparable to the changes in the saliva flow rate. There were no changes in salivary SIgA concentrations during the camp. These results suggest that using a chlorella-derived dietary supplement attenuates the reduced salivary SIgA secretion during a training camp for a competitive sport like kendo.
We investigated the immune-enhancing effects of a chlorella-derived dietary supplement by determining the salivary SIgA secretion rates. Salivary SIgA is the first line of defense against respiratory tract infections, such as pneumonia and influenza
. Recently, Yamauchi et al. investigated salivary SIgA secretion rates, Epstein–Barr virus (human herpes virus) DNA levels in saliva, and the number of upper respiratory symptoms during a 1-month training camp for rugby football. They found that the salivary SIgA secretion rate was reduced on the day before the first expression of Epstein–Barr virus DNA and that the number of symptoms increased after DNA expression. Fahlman et al. also reported that the salivary SIgA secretion rates were lower and the percent of subjects with upper respiratory tract infections was higher among university football players after they completed 6 weeks of very intensive training or 10 weeks of intercollegiate competition as compared to the beginning of the season and a period of rest and to a non-varsity group. The salivary SIgA concentration is also a good index for mucosal immune function. Gleeson et al. reported that the mean salivary SIgA concentration during a 7-month training period for elite swimmers was inversely related to the number of infections contracted. However, salivary SIgA concentrations are unsuitable for investigating any acute effects of exercise training because exercise can affect the saliva flow rate, as demonstrated in this study. Indeed, Gleeson et al. reported that salivary SIgA concentrations before an exercise session were related to the numbers of infections, but the concentrations immediately after the session were not. In light of this, we used the salivary SIgA secretion rate as an index for immunological depression induced by the kendo training camp.
In a previous study, we found that the salivary SIgA secretion rate increased after 4-week intake of a chlorella-derived supplement and that this increase derived primarily from the salivary SIgA concentration
. However, in the present study, we found no differences in the salivary SIgA secretion rates and concentrations before the camp between the placebo and chlorella groups. Because the salivary SIgA secretion rates before the camp, even in the placebo group, were higher than that we observed in our previous study
, the potential for improving the salivary SIgA secretion might have been minimal. In addition, the camp-related decease in salivary SIgA secretion and its attenuation due to chlorella intake were due to changes in saliva flow rates. A possible reason is that a reduced salivary SIgA concentration was offset by a decrease in the saliva flow rate, which could result in no change in salivary SIgA concentrations. Bogu (i.e., protective armor) obstructs the skin surface for evaporation and leads to heat accumulation
. A greater transpiration of saliva during kendo practice than during rest may be a reason for the marked decrease in saliva flow rates. However, these are only speculations. Additional studies will be needed to account for the mechanisms responsible for these discrepancies.
Because saliva samples were collected from the end of the morning training session to lunch during the camp, we consider that the acute and cumulative effects were included in the reduced salivary SIgA secretion during the camp. It is possible that reductions in salivary SIgA secretion after high-intensity exercise are mediated by a cytokine secretory function of T-cells via their expression of polymeric Ig receptors (pIgR) and by autonomic nerve activity via saliva secretion as a vehicle for SIgA. Kimura et al. showed that a brief round of intense exercise resulted in reducing the expression of pIgR mRNA in the submandibular gland, which paralleled a reduced salivary SIgA concentration. In the present study, the saliva flow rate reductions during the training camps were greater than the decreases in salivary SIgA concentrations. Thus, it is possible that the effects of chlorella intake on salivary SIgA secretion during the training camp may be more closely related to autonomic nerve regulation than to T-cell function.
Immune function is related to various nutrients, such as proteins
, and folate
. With regard to proteins, the SIgA concentrations in saliva and nasal secretions were reportedly lower in protein-calorie malnourished children than in healthy children
[17, 19]. However, this improved with nutritional support in a hospital
. Vitamin A deficiency has also been shown to decrease SIgA concentrations in the saliva
 and intestinal fluids
 of experimental animals. In addition, a combined deficiency of pyridoxine, a vitamin B6 compound, and pantothenic acid reportedly resulted in decreased antibody titers in human sera
. From a multicomponent analysis of the chlorella tablets we used, all of these nutrients were detected. Other nutrients that showed possible immune-enhancing effects in previous studies were also detected in chlorella tablets. Unfortunately, in this study, we could not determine which nutrient(s) attenuated the reduced salivary SIgA secretion during the training camp. However, it is reasonable that a wide spectrum of nutrients contributed to maintaining salivary SIgA secretion during the camp, as the individual components were not taken in large doses.
Various dietary supplements have been tested for their ability to attenuate immunological depression following intensive exercise. However, the reported effects of most nutrients were either negative or controversial; only two nutrients, carbohydrate and quercetin, have been recommended by the international society that specializes in exercise immunology
. Moreover, use of carbohydrate supplements before and/or during prolonged exercise has little effect on salivary SIgA secretion
. The effect of quercetin on SIgA secretion remains unclear
[29, 30]. Thus, dietary supplements that can attenuate the reduced SIgA secretion during a training camp have yet to be proposed. In this study, the chlorella-derived multicomponent supplement attenuated the decrease in salivary SIgA secretion during the kendo training camp, which suggests that supplementation with a mixture of various nutrients may be an efficient method to lower the infection risk in athletes. However, there may be a better composition for infection control in athletes. The next step will be to investigate changes in the serum concentration of nutrients that can affect SIgA secretion and determine the mechanisms involved in the observed effect of chlorella intake in order to determine the best nutritional composition of a dietary supplement for athletes.
This study had several limitations. First, there were differences in the conditions between the spring and summer camps (e.g., number of days and afternoon work-out times). Also, it is possible that the eating habits of our subjects changed during the experimental period and were different between the spring and summer trials. However, we randomly divided our subjects into (1) a spring camp with placebo and summer camp with chlorella group and (2) a spring camp with chlorella and summer camp with placebo group. In addition, we asked the subjects not to change their eating habits during the respective experimental periods (i.e., from the beginning of tablet intake to post-camp saliva sampling). Thus, we consider that the effects of the differences in the conditions between the spring and summer camps on our inter-group comparisons were not remarkable. Second, we calculated saliva flow rates based on mass rather than measuring the actual volume. Because the reported specific gravity of saliva in healthy young humans is approximately 1.003, the saliva flow rate and the salivary SIgA secretion rate would have been only slightly overestimated
[31, 32]. However, the body masses of our subjects did not decrease during the camps compared with their baseline values. A previous study reported that an exercise-induced loss of body mass of 1.1% did not change saliva osmolality
. Thus, it was possible to compare these indices obtained before the camp with those during and after the camp. Finally, it is possible that the timing of saliva sampling (before breakfast or before lunch) affected salivary SIgA secretion. A previous study demonstrated that the salivary SIgA concentration was not stable and was higher during the 2 h after awaking, especially during the first 30 min, compared to 3 to 10 h later
. However, the tendencies for our samples collected only before and during the summer camp (i.e., samples obtained with the same timing schedule) were nearly identical to those for all samples.