Chlorella is a type of one-celled green algae (a primitive plant) and is considered one of the kinds of "green foods" used to supplement the diet for health, prevention of certain diseases, and treatment of certain diseases.[1, 2]
Types of "green foods" used to supplement the diet include: [1,2]
Spirulina, another type of green algae
Chlorella and spirulina are taken as supplements in capsule, softgel capsule, tablet, granule, or liquid form or in special types of pasta.[1, 2] Blue-green algae are available as supplements. Barley grass and wheat grass, which are types of cereal grasses, are available fresh, as drinks, or as supplements.
Green foods have many nutritional and health benefits. For example, chlorella is rich in protein, chlorophyll, carotenoids, and omega fatty acids.[1-3] Chorella contains more chlorophyll than any of the other green foods.
Due to its ability to re-balance disturbed functions of the body, chlorella has been termed, "the great normalizer," due to its ability to re-balance disturbed functions of the body. Based on interpretation of studies conducted mostly in the laboratory and in animals, integrative medicine experts believe that the benefits of chlorella include assisting in the following functions, which may help prevent and aid in overcoming various types of cancers and other medical conditions:[1-6]
Prevent the action of chemicals that could otherwise cause cancer
Inhibit the growth of cancer cells
Boost the immune system
Prevent chemotherapy-induced decrease in white blood cells
Due to enhancement of the immune system, improve length of survival in studies in breast cancer, leukemia, and recipients of chemotherapy
Detoxify the body
Protect the lining of the stomach from side effects of drugs and irritants
Aid digestion of food
Promote the growth of normal flora (microbes) in the intestinal tract
Maintain the health of the liver
Protect DNA in normal cells against damage caused by radiation
Reduce the side effects of the chemotherapy drug, 5-fluorouracil
Speed wound healing and tissue repair via topical application or supplementation in diet
Chlorella's ability to boost the immune system includes:[1-6]
Protecting against chemotherapy-induced decrease in white blood cells
Increasing the amount of natural killer immune cells that fight abnormal cell
Enhancing the action of other T cells in lymph nodes against abnormal cells
Increasing the number of B cells, the antibody-producing cells
Enhancing the amount of macrophages (another type of white blood cell)
Promoting the production of gamma interferon and interleukin-1-alpha
Improving length of survival in studies in breast cancer, leukemia, and recipients of chemotherapy
The ability to bind to and remove heavy metals from fluids or tissues is called chelation. Substances that bind to and remove heavy metals from fluids or tissues are termed chelators or chelating agents.
Chlorophyll and the fibrous part of Chlorella have the ability to remove the following types of harmful chemicals from the blood, spleen, liver, and other tissues:[1-6]
Heavy metals (e.g, mercury, lead, cadmium, and arsenic)
Pesticides (e.g, DDT)
Other chemical toxins (e.g., PCB)
For example, in people taking chlorella supplements to reduce the level of mercury in their bodies, the mercury from tissues enters the intestine and is excreted in the feces. 
See the Q&A on "Benefits of Green Foods" for discussion of use of chlorella for other medical conditions.
Although chlorella has many health benefits, some people using chlorella may experience certain of the following side effects:[1, 6]
Sensitivity to sunlight
Gas, abdominal cramping, constipation, diarrhea, or nausea. Approximately one-third of people taking chlorella supplements do not tolerate it due to these gastrointestinal side effects. However, supplementation with cellulase may aid digestion of chlorella and help reduce these side effects of chlorella.
Fatigue, lethargy, or emotional irritability. These symptoms may be side effects of elimination of heavy metals from the body.
As chlorella and other green foods can stimulate the removal of certain chemicals from the body, it is possible that supplementation with chlorella or other green foods might interfere with the effects of chemotherapy drugs or radiation therapy on cancer cells.
Due to the high content of vitamin K in chlorella, interference with the effects of the anticoagulant, coumadin (warfarin), may occur. If you are taking coumadin, consult your physicians before considering taking chlorella or other green foods.
Before using any green foods including chlorella, consult your oncologists, your integrative medical physician, and your certified clinical nutritionist to determine whether supplementation or topical use is right for you and, if so, to recommend an appropriate dosage. Depending on the medical purpose, recommended doses of chlorella have ranged from 3 grams daily to 30 grams daily.[4, 6]
1. Chlorella. PDR Health. Accessed at www.gettingwell.com/drug_info/nmdrugprofiles/nutsupdrugs/chl_0068.shtml.
2. M. Adams. UCB Wellness Letter authors remain nutritionally illiterate about chlorella, spirulina, and blue-green algae. Accessed at www.newstarget.com/001697.html.
3. Chlorella. Tuberose Natural Healing Store Accessed at www.store.yahoo.com/helthequip-store/nabach.html.
4. Chlorella. Accessed at http://watershed.net/chlorella.htm
5. Chlorella. Troubled Times. Accessed at www.zetatalk.com/food/tfood27t.htm
6. J Mercola. Chlorella: A natural wonder food. Accessed at www.mercola.com/chlorella.