Chlorophyll

Chlorophyll is any of several closely related green pigments found in the chloroplasts of plants and algae and in cyanobacteria ^[1]. Its name comes from Greek words meaning pale green and leaf ^[1]. The pigment is the workhorse of photosynthesis: it absorbs sunlight most strongly in the blue and red parts of the spectrum and reflects green light, which is why leaves look green, and it channels the captured energy into the reactions that convert carbon dioxide and water into sugars ^[1]. Within the light-harvesting complexes, chlorophyll molecules both gather light and pass the energy along to reaction centers where charge separation begins ^[1].

Structurally, every chlorophyll is based on a chlorin ring, a large nitrogen-containing ring system related to the porphyrins that also form the core of heme in blood, but with a magnesium ion held at its center instead of iron ^[1]. Most forms carry a long hydrocarbon tail called a phytyl chain that anchors the molecule in cell membranes ^[1]. Several variants exist, the most widespread being chlorophyll a and chlorophyll b, with additional forms labeled c, d, and f occurring in particular organisms ^[1]. The pigment was first isolated and named by the French scientists Pierre Joseph Pelletier and Joseph Bienaime Caventou in 1817, and its magnesium content was established in the early twentieth century ^[1].

For food and supplement use, natural chlorophyll is often replaced by chlorophyllin, a mixture of water-soluble, semisynthetic salts made from chlorophyll, in which the central magnesium is typically exchanged for copper ^[2][3]. Chlorophyll and chlorophyllin are permitted food colorings, listed among the green additives used to tint products such as pasta, drinks, and liqueurs ^[1]. Chlorophyllin has also long been sold as an over-the-counter remedy, historically to control body and fecal odor, and more recently liquid chlorophyll supplements have been marketed for general wellness and skin ^[2].

Scientific interest has centered on chlorophyllin's antioxidant and anticancer, or chemopreventive, properties ^[2][3]. In laboratory and animal studies it acts as an antioxidant and can bind to certain carcinogens, among them aflatoxins, polycyclic aromatic hydrocarbons, and heterocyclic amines, forming complexes that reduce how much of the toxin the body absorbs ^[2][3]. This effect was tested in people in a randomized, placebo-controlled trial in a region of China with high liver-cancer risk from aflatoxin-contaminated food; taking chlorophyllin with meals lowered a urinary marker of aflatoxin damage to DNA by roughly half ^[4]. Reviewers caution, though, that results have sometimes conflicted, that much of the evidence is preclinical, and that broader health claims for chlorophyll supplements are not well established ^[2][3].

Natural chlorophyll is a normal and safe component of green vegetables, and chlorophyllin is regulated as a food additive and as a supplement or over-the-counter product rather than as an approved treatment for disease ^[1][2]. It is generally well tolerated, with the most common effects being harmless green discoloration of the stool or urine and occasional mild digestive upset; sensitivity of the skin to sunlight has also been reported ^[2]. Concentrated supplements have not been shown to deliver the specific benefits often claimed for them ^[2].

Generally safe. It can cause green discoloration of stool and urine, mild GI upset, and occasional diarrhea. High doses aren't well studied. Photosensitivity is a theoretical concern with some chlorophyll derivatives. It's benign for most people at typical doses.