An attempt to induce an immunomodulatory effect in rowers with spirulina extract which was published in 2018.
The study concluded that spirulina consumption may protect athletes against a deficit in immune function, and may cause a beneficial shift in your "overtraining threshold" (which is the level or amount of exercise at which overtraining occurs).
Signs of overtraining include:
Spirulina can help increase your endurance and help with the overtraining threshold.
The double-blind study included 19 members of the Polish Rowing Team. The subjects were randomly assigned to the supplemented group receiving 1500 mg of spirulina extract for 6 weeks, or to the placebo group.
The participants performed a 2000-m test on a rowing ergometer at the beginning and at the end of the supplementation period. Blood samples were obtained from the antecubital vein (in the arm) prior to each exercise test, 1 min after completing the 2000-m test, and after a 24 hour recovery period.
"Our present study showed, for the first time, that supplementation with SPR may modulate some components of the immune system in athletes exposed to repeated strenuous exercise. The fact that rowers from the supplemented group did not show a post-exercise increase in Treg count implies that Spirulina may play a role in maintaining normal tissue level of these cells during strenuous exercise, thus preventing immunosuppression. Moreover, Spirulina seemed to attenuate a suppressive effect of Tregs on CTLs, since during the 2nd examination, athletes from the supplemented group presented with significantly lower pre-exercise and post-exercise values of Treg/CTL ratio than subjects from the placebo group. Finally, strenuous physical exercise did not exert a significant effect on Tδγ cell count in the supplemented group, whereas athletes from the placebo group showed a post-recovery decrease in this parameter. Altogether, these findings suggest that supplementation with Spirulina may exert a beneficial effect on selected components of the immune system in athletes exposed to heavy training loads."
On the 2nd examination, athletes from the supplemented group showed neither a post-exercise increase in Treg count nor a post-recovery decrease in Tδγ cell count (both observed in the placebo group), and presented with significantly lower values of Treg/CTL prior to and after the exercise. During the same examination, rowers from the placebo group showed a significant post-recovery increase in Treg/(NK + Tδγ + CTL) ratio, which was absent in the supplemented group.