Scientific Name(s): Spinacia oleracea L. Family: Chenopodiaceae
Common Name(s): Spinach
Many of the reported actions of spinach are related to its antioxidant properties. It may play a role in the prevention of cancer, cardiovascular disease, age-related macular degeneration, and the degeneration of the immune and neurological systems.
There is no clinical evidence to support a specific therapeutic dosage of spinach. As a food, spinach has US Food and Drug Administration (FDA) generally recognized as safe (GRAS) status.
Contraindications have not been identified.
GRAS when used as food. Avoid dosages above those found in food because safety and efficacy are unproven.
Bioavailability of vitamin K from spinach is limited. While a simple meal containing spinach can result in a statistically significant reduction in the international normalized ratio (INR), the decrease is not likely to be clinically important. Absorption of magnesium, calcium, and zinc, but not nonheme iron, may be decreased by concurrent consumption of oxalates in spinach.
Allergic reactions to spinach are rare. Gout may be precipitated in predisposed individuals because of the purine content. Consumption of spinach in infants younger than 4 months is not recommended because of the potential for reduced calcium absorption. Contamination with Escherichia coli has resulted in outbreaks of food-borne illness.
Research reveals little or no information regarding toxicology with the use of spinach.
The Chenopodiaceae family consists of 100 species of evergreen or semievergreen annuals, perennials, and shrubs. Other members of this group include beet and chard. In temperate climates, spinach reaches edible maturity quickly (37 to 45 days) and thrives best during the cool, moist seasons of the year. There are a number of varieties of spinach, all of which have large, dark-green leaves on upright plants. The leaves are the most frequently used part of spinach. 1 , 2
Spinach contains a number of antioxidants, including carotenoids, polyphenols, 3 , 4 and flavonoids (quercetin). 5 The carotenoids are composed of 2 main classes, carotenes (beta-carotene) and xanthophylls (lutein). 6 Glycolipids (sulfoquinovosyl diacylglycerol) are found in the chloroplast membrane. 7 Spinach is regarded as a valuable dietary source of vitamin A, nonheme iron, folate, and lutein. Studies show much intrinsic variation in the bioavailability of these substances and variations caused by cooking methods. 8 , 9 , 10 , 11 , 12 Spinach also contains oxalates and nitrates that may have negative effects. 13 , 14 , 15 , 16
Uses and Pharmacology
Activity of spinach has mostly been attributed to its antioxidant mechanisms. 6 , 17 , 18 , 19 Although consumption of spinach increases the levels of plasma lutein, nonsignificant changes in plasma beta-carotene, retinol, and the metabolite retinoic acid have been noted, while the antioxidant capacity of plasma has not been shown to increase. 20 , 21Cancer
Several epidemiological studies suggest an association between spinach consumption and the inhibition of cancer. 5 , 22 , 23 , 24 , 25 , 26 In vitro experiments and clinical studies evaluating the potential role of spinach and/or spinach extracts in cancer are limited. 7 , 27Animal data
An antioxidant extract derived from spinach leaves reduced the multiplicity of papillomas in a mouse model ( P < 0.01). 28 This same extract has been used in several experiments demonstrating a dose-dependent inhibitory effect on human prostate cancer cell proliferation. 4 , 23 , 27 , 29 Certain fractions of spinach extracts exert a suppressive effect on gastric cancer cell cycle proliferation. 7 , 30 , 31 Spinach glycoglycerolipids have been shown to inhibit angiogenesis in human cell lines and in mouse tumor models. 32Clinical data
Tomatoes, carrots, and spinach powder given daily to healthy volunteers for a 2-week period suppressed DNA strand breaks. It has been proposed that these plant products exert their cancer-protective effect via a decrease in oxidative and other damage to human DNA. 3Cardiovascular disease
Analysis of the landmark Framingham Heart Study showed that an increased consumption of fruits and vegetables, the dominant source of folate in the human diet, was associated with higher levels of plasma folate, lower levels of plasma homocysteine, and a reduced risk of cardiovascular disease. Spinach consumption can increase plasma folate concentration 33 ; however, spinach is only one of many potential dietary factors.CNS effects
An improvement in delayed eye-blink conditioning (an Alzheimer disease model) has been demonstrated in rats fed spinach. 36 Mechanisms by which spinach might act are related to modulation of age-related increases in inflammatory response. 36 , 37Clinical data
There are no clinical data regarding the use of spinach for neurological dysfunction.Ophthalmic effects
Studies in the 1940s and 1950s showed that xanthophylls improved night vision and adaptation to dusk. Lutein and zeaxanthin, abundant in green leafy vegetables such as spinach, are highly concentrated in the macula of the eye and are believed to limit tissue damage by absorbing blue light.Animal data
There are no animal data regarding the use of spinach for age-related macular degeneration.Clinical data
Studies have shown that diets rich in lutein and zeaxanthin may lower the risk for age-related macular degeneration and could have a role in cataract prevention. Inhibition of lipid peroxidation and its chemical oxidation by free radicals is the suggested mechanism of action. 6 , 17 , 18Other
An epidemiological study among young Japanese women found an association between low bone mass and reduced daily intake of yellow and green vegetables. 38Immune system effects
Spinach is a dietary source of the carotenoid antioxidants beta-carotene and lutein, and thus, is postulated to help maintain immune cell integrity by reducing reactive oxygen species. 19Satiety
Membrane proteins (thylakoids) from the leaves of spinach have been evaluated in rats and healthy adults for effect on satiety. In rats, hydrolysis of triacylglycerols suppressed food intake, and reductions in body weight gain have been observed. In adults, satiety hormones cholecystokinin and leptin were reduced and the hunger hormone ghrelin was reduced after a single meal enriched with thylakoids. 39Vaccine
There is no clinical evidence to a support a specific therapeutic dosage of spinach. As a food, spinach has GRAS status; however, overconsumption may pose a potential risk because of the presence of nitrates in the vegetable. 27
GRAS when used as food. Avoid dosages above those found in food because safety and efficacy have not been established.
Warfarin interferes with the hepatic synthesis of vitamin K-dependent coagulation factors. Fluctuations in vitamin K intake can cause changes in anticoagulant response. Because spinach has a high vitamin K content, it can decrease the INR in patients taking oral anticoagulants 42 ; however, bioavailability of the vitamin K content is low. Studies in patients receiving warfarin with single meals of spinach resulted in a statistically significant, but not clinically important, reduction in the INR. 43 , 44 , 45
Absorption of magnesium, calcium, and zinc may be decreased by concurrent consumption of oxalates. Decreases in magnesium absorption have been demonstrated in healthy adults, but this is likely to be offset by the magnesium content of spinach. No decrease in nonheme iron absorption by oxalates has been shown in experiments. 14 , 46 , 47
Allergic reactions to spinach are rare, with very few case reports in the literature. 47 Immunoglobulin E–mediated allergy to spinach 47 and sensitization to spinach powder 48 have been reported. Crossreactivity to molds, mushrooms, and latex have been described, making it difficult to implicate spinach. 48 , 49 , 50 , 51 Additionally, spinach contains histamine, which can cause pseudoallergic reactions. 48 Because uric acid is a product of purine catabolism and spinach contains moderate amounts of purines, dietary reduction of purine intake may be appropriate in individuals predisposed to gout. 52 , 53 Spinach is not recommended in infants younger than 4 months because the oxalate content could reduce calcium absorption. 13 , 14 , 15 Methemoglobin formation is also possible through the plant's nitrate content. 16 Spinach has been implicated in outbreaks of E. coli food poisoning, including the fall 2006 outbreak in the United States that resulted in approximately 100 hospitalizations and 3 deaths. Contamination may occur via organic fertilizers or irrigation water or in postharvesting processing and bagging. 54 , 55 , 56
There is little or no information regarding toxicology with the use of whole spinach leaves. An antioxidant extract derived from spinach leaves was nonmutagenic. Toxicological studies performed on this extract in mice, rats, and rabbits showed no toxicity, adverse reactions, or abnormalities. 27
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