Chlorella is a freshwater green microalga sold as a powder or tablets. Trials suggest possible small benefits for cholesterol, blood pressure and immune markers, but the evidence is mixed: a 2018 meta-analysis of 19 trials found modest improvements, while a 2025 analysis of 12 trials found no clear effect. Compared with spirulina, chlorella is a different organism, some products contain active vitamin B12, and it is high in vitamin K, which matters if you take warfarin.
If you are choosing between two green powders on a shelf, or wondering whether chlorella is worth adding next to the spirulina you already have, this guide is for you. You will find what each one is, what trials found, a side-by-side table, trial doses, a recipe and the safety points that actually matter.
What is chlorella?
Chlorella is a single-celled green alga that grows in fresh water. Unlike spirulina, which is a cyanobacterium, chlorella is a true plant-like microalga with a nucleus. It contains protein, fibre, carotenes, vitamins, minerals and a lot of chlorophyll, which is why the powder is such a deep green.
You will find it as powder, small pressed tablets or capsules. The taste is grassy and slightly bitter, something you will want to mix into food.
What are the health benefits of chlorella?
Cholesterol and blood pressure: two meta-analyses disagree
A 2018 meta-analysis in Clinical Nutrition pooled 19 randomised trials with 797 people. Chlorella lowered total cholesterol by about 9 mg/dL, LDL cholesterol by about 8 mg/dL, systolic blood pressure by about 4.5 mmHg, diastolic pressure by about 1.6 mmHg and fasting glucose by about 4 mg/dL. Triglycerides, HDL cholesterol and body mass index did not change.
A 2025 meta-analysis in Nutrients looked at 12 chlorella trials, with 168 to 279 participants per outcome, and found no effect on any blood lipid or blood pressure measure. The same paper found a small effect of spirulina on diastolic pressure only, and called the overall evidence scarce and heterogeneous.
The honest summary: if chlorella helps your heart markers, the effect is small, and it is not a substitute for diet changes or medication. Your overall eating pattern matters more than any powder, and the Mediterranean diet is a well-studied place to start.
Immune markers
In a 2012 Korean trial, 51 healthy adults took 5 g of chlorella or a placebo daily for 8 weeks. The chlorella group showed higher natural killer cell activity and higher levels of some immune signalling molecules (interferon gamma, interleukin 1 beta and interleukin 12). That is a change in lab markers in one small study. It does not show that chlorella prevents colds or other infections, and the authors called for larger, longer trials.
Vitamin B12: depends on the product
This is where chlorella differs most from spirulina. According to a 2014 review on plant sources of vitamin B12, chlorella tablets can contain biologically active B12, but the amount varies hugely between brands, from zero to several hundred micrograms per 100 g. Spirulina, by contrast, contains mostly an inactive look-alike called pseudovitamin B12. If you follow a Vegane Diät, chlorella is not a safe replacement for a B12 supplement, because you cannot tell from the shelf which kind of product you have. The same review names dried nori as the most suitable plant source of B12 found so far.
Gewichtsverlust
People search for chlorella for weight loss, but the 2018 meta-analysis found no change in body mass index. There is no good evidence that it helps you lose weight.
Chlorella vs spirulina: what is the difference?
| Feature | Chlorella | Spirulina |
|---|---|---|
| What it is | Freshwater green microalga | Cyanobacterium (“blue-green alga”) |
| Vitamin B12 | Active B12 in some products, from zero to several hundred µg per 100 g | Mostly inactive pseudovitamin B12 |
| Blood pressure trials | 2018: systolic about -4.5 mmHg (19 trials); 2025: no effect (12 trials) | 2025: small effect on diastolic pressure only (9 trials) |
| Cholesterol trials | 2018: LDL about -8 mg/dL; 2025: no effect | 2025: non-significant trend for total cholesterol |
| Doses used in trials | 1.5 to 8 g a day | 0.2 to 8 g a day |
| Vitamin K and warfarin | High vitamin K, may reduce warfarin’s effect | About 1.8 µg per tablespoon (USDA) |
| Toxin contamination data | Not tested as products in a 2017 toxin study (used only as a blank reference) | 3 of 14 products had low levels of microcystins in the same study |
Sources: Fallah et al., Clinical Nutrition 2018; Pinto-Leite et al., Nutrients 2025; Watanabe et al., Nutrients 2014; LactMed (NIH) Chlorella; Roy-Lachapelle et al., Toxins 2017. Spirulina vitamin K from USDA FoodData Central, FDC ID 170495.
Which one should you choose?
Neither is essential. If blood pressure is your main interest, spirulina has slightly more consistent trial data, and our guide to spirulina benefits, side effects and dosage covers it in detail. If you take warfarin, spirulina is the easier choice because it is low in vitamin K. If B12 is your interest, neither is reliable: take a real supplement. And if you want a green powder mostly for the colour and a little extra iron, compare both with moringa powder, a leaf powder.
Can you take spirulina and chlorella together? Many blends combine them. We found no trials that tested the combination, so treat a blend as the sum of both sets of precautions.
How much chlorella should you take per day?
There is no official dose. Trials in the 2025 review used 1.5 to 8 g a day, and the Korean immune study used 5 g a day for 8 weeks. A careful approach:
- Week one: 1 g a day, with a meal.
- Then: 2 to 3 g a day if your digestion is fine.
- Upper end: about 5 g a day, which is what the immune study used.
Tablets are often small, so 3 g can mean a surprising number of them. Read the label and count milligrams, not tablets.
What does Ayurveda say about chlorella?
Chlorella is a modern food and is not described in classical Ayurvedic texts. Modern practitioners read it by its qualities. Its taste is bitter (tikta) and slightly astringent (kashaya), and these tastes are traditionally considered cooling (sheeta virya), drying and light. In that reading it would suit Pitta and Kapha better than Vata, and it is best taken with warm food at midday, when agni, the digestive fire, is considered strongest.
This is a traditional way of thinking about food, not scientific evidence. If you want to compare green powders with everyday foods, our honest superfoods list is a good reality check.
How to use chlorella: green tahini dressing
Chlorella’s grassy taste works well with tahini, lemon and Knoblauch. This makes enough for two salads or a bowl of warm lentils.
Zutaten
- 2 tablespoons tahini
- juice of half a lemon
- 1 small garlic clove, grated
- 3 to 4 tablespoons warm water
- 1 teaspoon chlorella powder (2 to 3 g)
- a pinch of salt and a pinch of ground cumin
Steps
- Stir the tahini and lemon juice together. It will thicken and look grainy; that is normal.
- Add the warm water a tablespoon at a time, stirring, until the dressing is smooth and pourable.
- Stir in the garlic, salt, cumin and chlorella until evenly green.
- Pour over a salad, roasted vegetables or warm lentils, and eat within a day.
For full days of eating built around foods like these, see our 7-day anti-inflammatory meal plan.
What are the side effects of chlorella and who should avoid it?
Common side effects
The NIH LactMed database describes chlorella as usually well tolerated, but lists digestive upset and green stools, plus reported allergic reactions and sensitivity to sunlight (photosensitivity). Starting with a small dose helps you notice problems early. If your gut is sensitive, our guide to gut health foods is a gentler place to start.
Warfarin and other blood thinners
LactMed notes that chlorella’s high vitamin K content may make warfarin less effective. If you take warfarin, do not start or stop chlorella without your doctor, and keep your intake steady if you do take it.
Autoimmune disease and immune-suppressing drugs
Chlorella raised immune markers in the Korean trial. Case reports have linked other immune-stimulating algae supplements, including spirulina, to flares of autoimmune disease. If you have an autoimmune condition or take immunosuppressants, ask your doctor first.
Iodine and thyroid conditions
We could not find reliable data on the iodine content of chlorella itself. Some green blends add marine seaweeds wie zum Beispiel Seetang, so if you have a thyroid condition, read the full ingredient list and ask your doctor before using a mixed product.
Product quality
In the US, supplements do not need approval for safety before sale, and LactMed warns that actual contents can differ from the label. In a 2017 study of 18 algae supplements, some spirulina and especially Aphanizomenon flos-aquae (AFA) products contained microcystin toxins, and the authors called for better quality control. Choose brands that publish independent lab tests.
Pregnancy and breastfeeding
LactMed considers chlorella probably acceptable during breastfeeding, though green-tinted breast milk has been reported. In pregnancy, ask your doctor or midwife first.
FAQ
Is chlorella better than spirulina?
Not overall. Chlorella may offer active B12 in some products, while spirulina is low in vitamin K and has slightly more consistent blood pressure data. The better choice depends on your medications and what you want from it.
Does chlorella remove heavy metals from the body?
This is a popular claim, but we found no good human trials that support it. If you are worried about heavy metal exposure, see a doctor for testing and proper treatment rather than relying on a supplement.
Can I take spirulina and chlorella together?
Many blends combine them. No trials have tested the combination, so start low, keep the total dose within the ranges used in trials and follow the precautions for both.
Is chlorella powder or tablets better?
The content is the same alga; the difference is convenience. Powder is easy to mix into food, while tablets avoid the taste but mean counting many small pills.
Sources
- Fallah AA, Sarmast E, Habibian Dehkordi S, et al. Effect of Chlorella supplementation on cardiovascular risk factors: A meta-analysis of randomized controlled trials. Clinical Nutrition, 2018. doi.org/10.1016/j.clnu.2017.09.019
- Pinto-Leite M, Martins D, Ferreira AC, et al. The Role of Chlorella and Spirulina as Adjuvants of Cardiovascular Risk Factor Control: A Systematic Review and Meta-Analysis of Randomised Controlled Trials. Nutrients, 2025. mdpi.com/2072-6643/17/6/943
- Kwak JH, Baek SH, Woo Y, et al. Beneficial immunostimulatory effect of short-term Chlorella supplementation: enhancement of Natural Killer cell activity and early inflammatory response. Nutrition Journal, 2012. link.springer.com
- Watanabe F, Yabuta Y, Bito T, Teng F. Vitamin B12-Containing Plant Food Sources for Vegetarians. Nutrients, 2014. mdpi.com/2072-6643/6/5/1861
- National Institute of Child Health and Human Development. Chlorella. Drugs and Lactation Database (LactMed), NCBI Bookshelf. ncbi.nlm.nih.gov/books/NBK501822
- Roy-Lachapelle A, Solliec M, Bouchard MF, Sauvé S. Detection of Cyanotoxins in Algae Dietary Supplements. Toxins, 2017. mdpi.com/2072-6651/9/3/76
This article is for information only and is not medical advice. If you have a health condition, are pregnant or take medication, talk to your doctor or pharmacist before changing your diet or starting a supplement.
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