Does chlorella help fight infection or viruses? What the research does and doesn't show

The evidence doesn't support chlorella as a way to fight off a virus or bacterial infection. The closest human trial gave chlorella to people already infected with hepatitis C and found a liver-enzyme change, but no significant drop in the virus itself; a separate trial in healthy adults measured immune cells, not whether people actually got sick less often.

What the evidence doesn't support

It doesn't support chlorella as a treatment for hepatitis C, the common cold, flu, COVID-19, or any other viral or bacterial infection — no trial has tested it against a diagnosed infection as the outcome measured. It doesn't support a "boosts immunity so you get sick less" claim either: the one trial that measured immune markers in healthy people never tracked whether they actually caught fewer colds or infections. And a change in a liver enzyme, seen in the hepatitis C trial below, isn't the same as a change in the virus itself, which is the part of that trial that didn't move significantly.

What the trials found

A 12-week, open-label trial (no placebo group) gave daily chlorella to 18 adults with chronic hepatitis C. By the end of the trial, most patients — about 85% — had a significant decrease in ALT, a liver enzyme commonly elevated by hepatitis C, and chlorella was well tolerated with most participants reporting better energy and general health on a quality-of-life questionnaire. But the level of hepatitis C virus RNA in the blood, the direct measure of the infection itself, did not change significantly, even though it trended down in most participants. Without a placebo group, it's also not possible to know how much of the ALT change would have happened anyway.

A separate, placebo-controlled trial gave 51 healthy adults 5 grams a day of chlorella tablets for 8 weeks and measured immune-system biomarkers in blood: natural killer cell activity and certain cytokines were higher in the chlorella group than placebo. That's a change in how active certain immune cells were in a lab test, in people who weren't sick to begin with — the trial never tracked whether anyone in either group actually caught a cold, flu or other infection during the study.

Questions people ask

Does chlorella help fight a virus?

The one trial run in people with an actual viral infection (hepatitis C) found a liver-enzyme change but no significant drop in the virus itself. No trial has tested chlorella against a cold, flu or other common virus.

Does chlorella boost the immune system?

One trial in healthy adults found higher natural killer cell activity and certain immune markers after chlorella versus placebo. That trial didn't measure whether participants got sick less often — it measured cells and markers in blood, not illness. See chlorella: what the research does and doesn't show for the same trial in more detail.

When to talk to a doctor

Chlorella is not a treatment for a viral or bacterial infection. If you have hepatitis C, another chronic infection, or a compromised immune system, talk to a doctor before adding chlorella, especially alongside prescribed antiviral or immune-modulating medication. A known algae allergy is also a specific reason to avoid it — see who should not take chlorella.