Chlorella is a single-celled green algae that grows in fresh and marine water and is sold as a nutritional supplement in tablet and powder form. It packs roughly 59% protein by dry weight, contains all the vitamins humans need, and is unusually rich in iron, making it one of the most nutrient-dense whole foods available. Most commercial products use either Chlorella vulgaris or Chlorella pyrenoidosa, two closely related species.
Nutritional Profile
Chlorella’s standout feature is its protein content. At 50 to 65 grams of protein per 100 grams of dry weight, it rivals or exceeds most plant-based protein sources. It also delivers a broad spectrum of vitamins: B1, B2, B6, B12, niacin, folate, biotin, pantothenic acid, C, D2, E, and K, plus both alpha- and beta-carotene.
The mineral profile is equally impressive. Commercially available chlorella products contain around 104 mg of iron per 100 grams of dry weight, though this varies widely between brands (some products list as high as 350 mg or more). Potassium runs close to 1,000 mg per 100 grams. Chlorella is also one of the richest natural sources of chlorophyll, the green pigment responsible for its deep color.
The main carotenoids in chlorella are lutein (the most abundant), beta-carotene, and zeaxanthin. A 6-gram dose of dried chlorella delivers about 7 mg of lutein, nearly 2 mg of beta-carotene, and roughly 1.5 mg of zeaxanthin. One study found that a single 6-gram dose raised blood levels of all three carotenoids for up to three days, suggesting the nutrients are well absorbed.
Why the Cell Wall Matters
Chlorella has an unusually tough cell wall that your digestive system cannot break down on its own. This wall acts as a strong barrier, locking nutrients inside. Supplement manufacturers crack the wall before packaging using methods like bead milling, ball milling, or sonication (high-frequency sound waves). When shopping for chlorella, look for labels that say “broken cell wall” or “cracked cell wall.” Without that processing step, much of the nutritional content passes through your body unused.
Heavy Metal Binding
One of chlorella’s most discussed properties is its ability to bind heavy metals. The cell wall and its insoluble fiber contain functional groups (carboxyl, amino, hydroxyl, and others) that have a high chemical affinity for metals like mercury, cadmium, and lead. In lab and animal studies, these compounds latch onto metal ions and help prevent them from interacting with cells. The insoluble portion of chlorella has been specifically linked to the removal of mercury, cadmium, and radioactive strontium from the body. Human evidence is more limited, but clinical trials have used doses of 9 grams per day for three months to study effects on mercury levels.
Immune System Effects
A randomized, double-blinded, placebo-controlled trial in healthy adults found that 8 weeks of chlorella supplementation significantly increased natural killer (NK) cell activity. NK cells are part of your innate immune system, responsible for identifying and destroying virus-infected cells and some tumor cells. The chlorella group also showed significant increases in interferon-gamma and interleukin-1-beta, two signaling molecules that help coordinate immune responses. The placebo group saw no such changes. The increases in NK cell activity correlated directly with the rises in these immune signals, suggesting a consistent biological effect rather than random variation.
Cardiovascular Benefits
A meta-analysis pooling 19 randomized controlled trials with 797 total participants found that chlorella supplementation reduced total cholesterol by about 9 mg/dL, LDL (“bad”) cholesterol by roughly 8 mg/dL, systolic blood pressure by 4.5 mmHg, and diastolic blood pressure by about 1.6 mmHg. Fasting blood glucose dropped by around 4 mg/dL. These are modest but statistically significant improvements.
The reductions were most reliable when people took chlorella for at least 8 weeks at doses above 4 grams per day. The benefits for cholesterol were more pronounced in people who already had elevated levels, and the blood pressure effects were strongest in those with existing hypertension. Triglycerides, HDL cholesterol, and BMI did not change significantly.
Typical Dosages
Most research suggests a daily intake of 3 to 10 grams for general health benefits. Clinical trials have used a range of specific doses depending on the goal: 5 grams per day for immune function, 6 grams per day for immune markers in saliva, 8 grams per day for antioxidant effects, and up to 9 grams per day for mercury-related studies. For newcomers, starting at the lower end (3 grams) and increasing gradually helps minimize digestive discomfort.
How Chlorella Compares to Spirulina
Chlorella and spirulina are both microalgae sold as supplements, but they differ in meaningful ways. Spirulina is a blue-green algae (technically a cyanobacterium) with a slightly higher protein concentration and a complete amino acid profile that’s often highlighted for athletes. Chlorella, on the other hand, contains significantly more chlorophyll, a broader vitamin profile, and the unique cell-wall compounds that give it metal-binding properties spirulina lacks. Chlorella also provides more iron. Spirulina grows only in alkaline freshwater, while chlorella species thrive in both freshwater and marine environments.
Side Effects and Cautions
The most common side effects are digestive: diarrhea, nausea, gas, and stomach cramping, particularly during the first week. Green-colored stools are normal and harmless, simply reflecting chlorella’s high chlorophyll content.
Chlorella can cause skin to become more sensitive to sunlight, so sunscreen is worth applying if you spend time outdoors, especially if you have lighter skin. Serious allergic reactions have been reported in rare cases, including asthma and breathing difficulties.
Because chlorella contains iodine, people with iodine sensitivity should be cautious. More importantly, chlorella stimulates immune activity. For most people that’s a benefit, but if you have an autoimmune condition like lupus, rheumatoid arthritis, or multiple sclerosis, increased immune activation could worsen symptoms. People with these conditions are generally advised to avoid chlorella.