We investigated the effects of 4-week ingestion of a chlorella-derived multicomponent supplement on salivary SIgA secretion using a blind, randomized, crossover study design. This is a first study to evaluate the effects of chlorella-derived supplement on mucosal immune functions in humans. The salient finding of this study is that both salivary SIgA concentration and secretion rate increased after 4-week chlorella supplementation compared to baseline. Similar changes were not identified in the placebo trial. We therefore concluded that oral supplementation with a chlorella-derived multicomponent supplement enhances mucosal immune function.
Salivary SIgA secretion was used to investigate the immunoenhancing effect of ingestion of a chlorella-derived multicomponent supplement. Salivary SIgA is the first line of defense against respiratory tract infections such as pneumonia and influenza . Klentrou et al.  reported that an increase in salivary SIgA concentration following 12 weeks of moderate exercise was related to a decrease in a number of sick days. Furthermore, Gleeson et al.  reported that a mean salivary SIgA concentration during a 7-month training period of elite swimmers was associated with a number of infections contracted during this period. Therefore, we believe that salivary SIgA concentrations and secretion rates are valid indices of mucosal immune function.
Several factors are responsible for reductions in nutrients and calorie intakes. Many studies have pointed out that a diminished sense of smell and taste, increased cytokine activity, altered gastrointestinal function, and altered hormone secretion may induce anorexia even in healthy older adults [29, 30]. Further, adverse social factors such as loneliness , psychological factors such as depression [11, 12], and medical factors such as poor dentition  may also cause undernutrition in older adults. In young adults, contributing factors include skipping breakfast [14, 15], relying on fast food [16, 17], and dieting to achieve a thin body [18, 19]. In particular, university students living away from home and those who have a sedentary lifestyle are at a higher risk of poor nutrition than students who live at home and participate in sporting activities . The majority of the participants in this study were university students. There exists a possibility that the participants had inadequate nutritional status and the nutrients in the chlorella-derived supplement attenuated their health problems. We can speculate, from lean body weight, body fat, and body mass index, that total calorie and protein intakes in the subjects were not insufficient. However, we could not investigate their eating habits and perform any blood chemical analysis. One of the next steps is to clarify the mechanisms responsible for the chlorella ingestion-induced increase in salivary SIgA secretion.
This study has following limitations. First, we could not investigate eating habits and perform any blood chemical analysis as mentioned above. Second, we have no data describing clinical significance of change in salivary SIgA secretion. Although it is possible that the dietary supplement-related additional antibodies in healthy young humans elevate a reserve of immune function, it may not improve their infection rate at normal condition. Intervention studies in humans with reduced salivary SIgA level like athletes during training camp and older humans are needed. This study is an initial step to elucidate the effects of chlorella-derived supplement on mucosal immune functions. Recently, Yamauchi et al.  reported an expression of Epstein-Barr virus-DNA in saliva and an increase in a number of upper respiratory symptoms occurred on the following day of approximately 23 percent reduction in salivary SIgA secretion rate, although this reduction was smaller than the increase by the chlorella supplementation in our study (41%). Again, the salivary SIgA secretion rate after the chlorella ingestion was 37 percent greater than that after the placebo intake. Therefore, we consider the elevation of salivary SIgA secretion rate in the chlorella trial was clinically significant. Third, we obtained saliva in the morning to equalize the conditions of subject among four sampling points (placebo or chlorella trials × before and after ingestions) although salivary SIgA level is not stable in the morning especially during 10 min after awakening . The saliva collection in this study was performed at least 1 hour after awakening, however, we can not rule out the effect of diurnal cycle in salivary SIgA secretion.