Chlorella

Chlorella is a genus of microscopic green algae in the division Chlorophyta, made up of roughly a dozen species of single-celled organisms ^[1]. The cells are spherical and only a few micrometers across, lack the whip-like flagella that many algae use to swim, and contain a chloroplast rich in the green pigments chlorophyll a and chlorophyll b ^[1]. The German microbiologist Martinus Beijerinck first described the genus in 1890, and its name combines the Greek word for green with a Latin ending meaning small ^[1].

Chlorella holds a notable place in the history of biology as a laboratory model for studying photosynthesis; researchers including Otto Warburg worked with it, and Melvin Calvin used it in the experiments on carbon dioxide assimilation that won him the Nobel Prize in Chemistry in 1961 ^[1]. After the Second World War, scientists explored Chlorella as a high-protein crop that might help feed a growing world population, since it grows quickly and, when dried, can be about half protein by weight ^[1]. Large-scale cultivation proved more difficult and costly than early enthusiasts predicted, and the grand food projections were never realized, but the alga remains commercially farmed in ponds and tanks ^[1].

As a food and supplement, Chlorella is valued for its dense and varied nutrient content, which includes protein, omega-3 polyunsaturated fatty acids, polysaccharides, vitamins, minerals, carotenoids, and a large amount of chlorophyll ^[2][4]. Because its natural cell wall is tough and hard to digest, supplement makers often process the algae to break or crack the wall and improve the availability of its nutrients ^[1]. It is sold mainly as pressed tablets and powders marketed for general wellness, and it is also used as feed in aquaculture and studied for wastewater treatment and biofuel ^[1][2].

Clinical interest has focused on whether Chlorella supplementation can improve markers of metabolic health ^[2][3]. Some trials suggest it may modestly lower blood lipids and blood sugar and reduce oxidative stress, and reviews have catalogued a range of proposed benefits ^[2]. However, a systematic review of randomized trials in people with obesity-related metabolic disorders found the results inconsistent and the studies generally too small to support firm conclusions ^[3]. Health authorities note that available scientific studies do not establish Chlorella as an effective treatment or preventive for cancer or other diseases in humans ^[1].

Chlorella is regulated as a food or dietary supplement rather than as a medicine, and product quality and nutrient content can vary with the strain and growing conditions ^[1]. It is generally considered safe as a food, but reported issues include digestive upset, especially when first starting it, and sensitivity of the skin to sunlight linked to its pigments ^[1]. Its cell walls contain lipopolysaccharides, bacterial-type endotoxins that can provoke immune responses, and the algae can act as an allergen in some people ^[1].

Generally safe, with common side effects being GI upset, gas, and green stools, especially when starting. It can cause photosensitivity in some people and may contain contaminants if poorly sourced, so quality matters. It is high in vitamin K, which can matter for people on warfarin.