Chlorella pyrenoidosa is a species of freshwater green algae commonly used as a dietary supplement. Its use to support or treat free radical damage is primarily justified by scientific studies, although the evidence is still preliminary and not robust. Chlorella contains high levels of antioxidants, such as chlorophyll, carotenoids (including lutein and beta-carotene), vitamin C, and vitamin E. These compounds are known to neutralize free radicals and reduce oxidative stress in vitro and in animal models.

Several laboratory and animal studies have shown that Chlorella supplementation can increase antioxidant enzyme activity (e.g., superoxide dismutase, catalase, and glutathione peroxidase) and decrease markers of oxidative damage. Limited human studies suggest that Chlorella supplementation may reduce oxidative stress, especially in populations exposed to higher oxidative challenges, such as smokers or individuals with chronic conditions. For example, a small randomized controlled trial found that Chlorella supplementation reduced markers of oxidative stress in smokers. However, the number of high-quality human trials is limited, and the sample sizes are often small.

In summary, Chlorella pyrenoidosa is used to support protection against free radical damage based on its antioxidant content and early scientific evidence. However, more rigorous clinical trials are needed to confirm these effects in humans and to better understand the clinical relevance of supplementation.