Potential of Chlorella as a Dietary Supplement to Promote Human Health
Tomohiro Bito,1 Eri Okumura,2 Masaki Fujishima,2 and Fumio Watanabe1,*
Author information Article notes Copyright and License information PMC Disclaimer
Abstract
Chlorella is a green unicellular alga that is commercially produced and distributed worldwide as a dietary supplement. Chlorella products contain numerous nutrients and vitamins, including D and B12, that are absent in plant-derived food sources. Chlorella contains larger amounts of folate and iron than other plant-derived foods. Chlorella supplementation to mammals, including humans, has been reported to exhibit various pharmacological activities, including immunomodulatory, antioxidant, antidiabetic, antihypertensive, and antihyperlipidemic activities. Meta-analysis on the effects of Chlorella supplementation on cardiovascular risk factors have suggested that it improves total cholesterol levels, low-density lipoprotein cholesterol levels, systolic blood pressure, diastolic blood pressure, and fasting blood glucose levels but not triglycerides and high-density lipoprotein cholesterol levels. These beneficial effects of Chlorella might be due to synergism between multiple nutrient and antioxidant compounds. However, information regarding the bioactive compounds in Chlorella is limited.
Keywords: antioxidants, Chlorella, dietary fibers, dietary supplements, folate, lutein, vitamin B12, vitamin D2
1. Introduction
Microalgae are primarily found in aquatic ecosystems, living in both seawater and freshwater, and are photosynthetic eukaryotic organisms that contain chloroplasts and nuclei, similar to plants. Microalgae more efficiently yield biomass than land-based plants owing to their higher performance in utilizing sunlight and CO2, leading to their extremely high growth rates [1]. Therefore, microalgae have been used in the food, pharmaceutical, and cosmetic industries, and their pigments, nutrients, bioactive compounds and whole biomass are already in use worldwide. Recently, various bioactive compounds and nutrients have been detected in both seawater and freshwater microalgae, including cyanobacteria. These compounds and nutrients have been reported to promote human health [1,2]. However, there is limited information regarding the bioactive compounds of freshwater-living Chlorella species, which are classified as green algae.
Chlorella species can be mass-cultured, and their dietary supplement products are commercially available worldwide. However, the commercial cultivation of their biomass has started only several years ago. Chlorella vulgaris was discovered and reported in 1890 by Dr. Martinus Willem Beijerinck, a famous microbiologist and botanist [3]. Another Chlorella species, distinguished by the presence pyrenoids in chloroplasts, was identified and accordingly named C. pyrenoidosa in 1903 [4]. Since then, more than 20 Chlorella species have been characterized, with over 100 strains described [5]. At present, Chlorella species are divided into three varieties: C. vulgaris, C. lobophora, and C. sorokiniana [6]. C. sorokiniana is a sub-species first isolated in 1953 by Sorokin and originally thought to be a thermotolerant mutant of C. pyrenoidosa [7,8]. C. pyrenoidosa, the subject of many scientific studies, is now called C. sorokiniana.
Investigations of the dietary value of Chlorella in human health began in the early 1950s, when the use of Chlorella as a food source was initiated in the midst of a global food crisis [9]. Chlorella was first produced and consumed in Asia, mainly in Japan, and then used as a dietary supplement worldwide [10]. Chlorella is produced commercially for use in foods and as a source of its intrinsic compounds. Using large-scale cultivation technology, C. vulgaris and C. pyrenoidosa are prepared as commercial sources for dietary supplements [11]. Studies have shown that Chlorella cells contain a variety of nutrients and bioactive compounds that promote human health and prevent certain diseases [10,12], suggesting that Chlorella-derived natural compounds might provide substitutes for synthetic compounds or drugs. The content of natural compounds in Chlorella differs greatly between culture conditions and Chlorella species [13,14].
Here, we present updated information on the Chlorella content of nutrients and bioactive compounds that promote human health. However, at present, there is limited information available regarding the bioactive compounds responsible for its pharmacological activities, which might be due to the synergistic effects of various nutrients and antioxidant compounds in Chlorella.
2. Nutrients in Commercial Chlorella Products
2.1. Macronutrients
The macronutrient content of 13 commercially available Chlorella products, based on information provided on the packaging label, are summarized in Table 1. Humans cannot digest Chlorella cells in their natural state because their cell walls are made of cellulose. Therefore, Chlorella cell walls are mechanically broken down in most dietary supplements. An animal study has shown that more than 80% of Chlorella proteins are digestible [15].
Table 1
Nutrient content of 13 commercially available Chlorella products.
| Macronutrients (Per 100 g Dry Weight) | A | B | C | D | E | F | G | H | I | J | K | L | M |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Proteins (g) | 50–65 | 61 | 63 | 65 | 57 | 50 | 56–72 | 50–67 | 50–70 | 62 | 60 | 58 | 57 |
| Fats (g) | 7–14 | 10 | 13 | 12 | 11 | 7–20 | 5–15 | 8–15 | 11 | 10 | 10 | 12 | |
| Carbohydrates (g) | 15 | 11 | 5–23 | 8–42 | 8–20 | 20 | 18 | ||||||
| Sugars (g) | 5–21 | 7 | 5 | 0–1 | 0–5 | 2–23 | 1–10 | 11 | |||||
| Dietary fibers (g) | 7–14 | 11 | 10 | 11 | 11 | 5–18 | 7–18 | 8–16 | 10 | ||||
| Remarks | *1 *2 78% | *1 *4 | *2 | *2 | *1 *2 77–82% *3 | *2 75–85% *3 | *1 *2 83% *3 | *2 82% *3 | *4 | *1 *3 *4 |
*1 Cell walls disrupted; *2 digestibility of proteins; *3 contains Chlorella extract; *4 C. pyrenoidosa.
These Chlorella products contain a large amount of proteins (approximately 59% based on dry weight), coinciding with the analytical data of the protein contents of C. pyrenoidosa (57%) [16] and C. vulgaris (51–58%) [17]. This protein content is higher than that of soybeans (approximately 33%, dry weight). The amino acid composition of Chlorella products C and M are shown in Table 2. These amino acid profiles indicate that all essential amino acids for humans (isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine, and histidine) are present in substantial concentrations in these products. According to the essential amino acid index (EAAI) used to evaluate protein quality for human nutrition, the quality of C. pyrenoidosa (EAAI, 1.35) [18] and a commercially available Chlorella product (EAAI, 0.92) [19] are higher than that of soybean protein (EAAI, 0.66) [18]. These results indicate that proteins in Chlorella products are of high or good quality. Notably, Chlorella products contain a considerable amount of arginine (approximately 3200 mg/100 g dry weight), which serves as a substrate for the production of NO, a potent intracellular signaling molecule that influences every mammalian system [20]. Arginine also serves as a potent modulator of immune functions [21].
Table 2
Amino acid content of commercially available Chlorella products C and M.
| Amino Acids (mg/100 g Dry Weight) | C | M |
|---|---|---|
| Essential | ||
| Isoleucine | 1820 | 2030 |
| Leucine | 4180 | 4480 |
| Lysine | 4659 | 3140 |
| Methionine | 1009 | 1240 |
| Phenylalanine | 2230 | 2580 |
| Threonine | 2209 | 2490 |
| Tryptophan | 1030 | 1090 |
| Valine | 2780 | 3090 |
| Histidine | 1141 | 1040 |
| Non-essential | ||
| Tyrosine | 1720 | 1940 |
| Cystine | 659 | 650 |
| Aspartic acid | 4469 | 4710 |
| Serine | 1930 | 2120 |
| Glutamic acid | 6209 | 6030 |
| Proline | 2320 | 2560 |
| Glycine | 2859 | 2990 |
| Alanine | 4009 | 4170 |
| Arginine | 3109 | 3260 |
Approximately 17% (dry weight) of carbohydrates are found in the commercially available Chlorella products. Similar results have been reported for C. vulgaris [17]. As shown in Table 1, more than 65% of the carbohydrate is dietary fiber, which appears to be derived from the Chlorella cell wall. Various polysaccharides have been extracted and characterized [22,23,24,25]. Chlorella polysaccharides exhibited a variety of biologically active compounds, including antioxidants [24] and stimulators of plant growth [25]. Tabarsa et al. [26] characterized an immune-enhancing water-soluble α-glucan prepared from C. vulgaris.
Commercially available Chlorella products contain a small amount of fats (approximately 11%, dry weight) (Table 1), which coincides with the analytical data of the fat content of C. vulgaris (14–22%) [17]. Chlorella products contain α-linolenic acid (approximately 10–16% of total fatty acids) and linoleic acid (approximately 18% of total fatty acids) but not eicosapentaenoic acid, docosahexenoic acid, or arachidonic acid [19,27]. Approximately 65–70% of the total fatty acids found in commercially available Chlorella products are derived from polyunsaturated fatty acids [19,27].
Different growth conditions, such as temperature, nutrient composition, and light availability, can readily alter the levels of biomass, macro- and micronutrients, and other valuable bioactive compounds, including antioxidants, in Chlorella cells [28,29,30].
