Especially if you have started exercising more (thumbs up for you, sir/ma'am), supplementation with spirulina might reduce your risk of a viral infection. According to a human study published in Biology in 2022, you need a dose of 6 grams of dried spirulina per day for this.

Study
Researchers from the University of Mohaghegh Ardabili in Iran divided thirty healthy young women into three groups. The women had a sedentary lifestyle and were on the heavier side. Their average BMI was 27-29.

Placebo + HIIT | The women in the first group completed high-intensity interval training [HIIT] three times a week. Each workout consisted of 4-7 sprints of 30 seconds. Between the sprints, the subjects walked for 30 seconds. Every day, the women drank a beverage without active ingredients.

Spirulina only | The women in the second group drank a beverage containing 6 grams of spirulina every day.

Spirulina + HIIT | The women in the third group did interval training three times a week and consumed 6 grams of spirulina daily.

Just before and just after the intervention, the researchers tested the women. Among other things, they determined their maximal oxygen uptake and took blood samples in which they determined the concentration of antibodies.

Results
In the groups that trained, the capacity to absorb oxygen increased; in the group that did not train, this hardly happened. However, the differences were not statistically significant. That may not tell the whole story in this case. The number of participants was small.

In the group that both trained and used spirulina, the increase was slightly greater than in the group that only trained. Those differences were also not statistically significant.

Click on the tables below for a larger version.

In the groups that received spirulina, the concentration of IgG antibodies in the women's blood increased. Again, the differences were not significant.

IgG antibodies are active in the body. For example, they capture viruses that have managed to penetrate the body.

IgA antibodies are active in the places where the body comes into contact with the outside world. IgA antibodies are found in the mucous membranes of the nose, mouth, and lungs, but also in the epithelium of the intestines. IgA antibodies are therefore part of the body's first line of defense against viruses and other pathogens.

Spirulina supplementation increased the concentration of IgA antibodies. This increase was statistically significant. Moreover, the increase was substantially greater in the group that used spirulina and also exercised. This may mean that intensive physical exercise and supplementation reinforce each other's effects.

Conclusion
"The data in the present study demonstrated the effectiveness of spirulina supplementation and HIIT concurrently in making significant changes in IgA concentrations [...]", the researchers summarize.

"Taking spirulina with HIIT for overweight and obese women may be helpful [...] for boosting IgA, which plays an important role in the immune system."