Spinach is famous for iron, and the usual story of why is itself partly a myth. The tale says a chemist put a decimal point in the wrong place and made spinach look ten times richer in iron than it is. A 2014 paper that traced the story to its roots found no evidence that the slip ever happened. Raw spinach has 2.7 mg of iron per 100 g, or 15% of the Daily Value, which is real but not unusual for a green vegetable.
Popeye is not the source of the iron idea: a 1932 strip credits vitamin A, not iron. Spinach also shows how a number on a label can differ from what your body takes in. It is high in oxalate, which binds calcium, and in a trial of 13 adults 5.1% of the calcium in spinach was absorbed against 27.6% from milk. Oxalate seems to matter much less for iron: in a trial in women, adding oxalic acid to a kale meal did not change iron absorption.
What spinach does stand out for is vitamin K, lutein and nitrate. A 100 g serving of raw leaves has 483 µg of vitamin K, which is 402% of the Daily Value, and only 2 of the 96 foods in our database has more per gram. It has 12,198 µg of lutein and zeaxanthin per 100 g, second among the 74 foods that list them. In 18 adults a spinach drink with 800 mg of nitrate raised blood nitrate to nearly the same level as beetroot juice did. On our nutrient density score, which counts 27 nutrients per 100 calories, spinach ranks first of all 143 foods, far above the 200 that counts as high.
Health benefits of spinach
The top findings from 30 studies, strongest evidence first
What the stars mean
- Strong. Several randomized trials, pooled in a meta-analysis, point the same way, or regulators (FDA or EFSA) have approved the claim.
- Moderate. Good randomized trials support it, but there are fewer of them, or their results vary.
- Limited. Small, short or single trials, or mixed results. Promising, but it needs confirmation.
Population and lab studies get no stars: they show a link or a mechanism, not proof.
How we rate evidence →- ★★Nitrate lowered blood pressure in healthy people onlyDietary nitrate, which spinach is rich in, lowered the top number by 2.4 mm Hg in healthy people (19 articles, not spinach alone). In people with raised blood pressure, 5 weeks of nitrate-rich leafy greens did not lower 24-hour pressure.
- ★★Lutein pills did not clearly slow macular degenerationAdding lutein and zeaxanthin to the standard eye vitamin formula did not significantly cut progression to advanced macular degeneration over about 5 years. This was a supplement, not spinach.
- ★Higher blood folate, more from minced spinachEating spinach for 3 weeks raised blood folate. Minced or liquefied spinach raised it more than whole leaves.
- ★Little calcium absorbed from spinachPeople absorbed 5.1% of the calcium in spinach, against 27.6% of the calcium in milk. This was a crossover trial in 13 healthy adults.
- ★Little of spinach’s soluble oxalate absorbedIn 10 volunteers, only about 1.9% of the soluble oxalate in grilled spinach was absorbed over 24 hours. Sour cream and milk lowered it further.
All 30 studies, strongest evidence first
Leafy green vegetables with 300 mg of nitrate a day for 5 weeks did not lower 24-hour blood pressure in people with raised pressure
Randomized trial in 243 people aged 50 to 70 with a clinic systolic pressure of 130 to 159 mm Hg, of whom 231 finished. Ambulatory systolic pressure fell 0.5 mm Hg on leafy greens, 0.6 on placebo and 1.2 on nitrate pills, and the differences were not significant. It tested leafy greens as a group, not spinach alone.
Dietary nitrate, which spinach is rich in, lowered systolic blood pressure by 2.4 mm Hg in healthy people but not in people with high blood pressure
Meta-analysis of 19 articles on randomized trials of dietary inorganic nitrate, not spinach alone. In healthy people diastolic pressure did not change significantly, and in people with hypertension systolic pressure fell only 0.8 mm Hg, which was not significant. The authors say more research is needed.
Adding 10 mg of lutein and 2 mg of zeaxanthin a day to the standard eye vitamin formula did not significantly cut progression to advanced macular degeneration over about 5 years
Randomized, placebo-controlled trial in 4,203 people aged 50 to 85 at risk of advanced macular degeneration. By 5 years 29% of eyes on lutein and zeaxanthin and 31% on placebo had progressed (hazard ratio 0.90, 98.7% confidence interval 0.76 to 1.07). This was a supplement, not spinach, but lutein and zeaxanthin are the main carotenoids in spinach.
A spinach drink with 800 mg of nitrate lowered systolic blood pressure by about 7 mm Hg 5 hours later in healthy adults
Crossover trial in 18 healthy adults (average age 28) who drank spinach, beetroot juice, a rocket salad drink or sodium nitrate, each with 800 mg of nitrate. Blood nitrate peaked at about the same level for all four (584 µmol/L for spinach), while sodium nitrate did not change blood pressure. Spinach lowered systolic pressure from 118 to 111 mm Hg at 300 minutes.
Eating spinach soup with 845 mg of nitrate a day for 7 days lowered brachial systolic blood pressure by 3.5 mm Hg 3 hours after the meal, compared with a low-nitrate soup
Placebo-controlled crossover trial in 27 healthy adults, using asparagus soup as the low-nitrate comparison. Central systolic pressure fell 3.4 mm Hg and diastolic 2.6 mm Hg, and the pressure drops showed after 7 days only. It was small, short and in healthy people.
A single spinach meal raised blood nitrite from 35 to 99 nmol/L and improved artery widening in healthy adults
Randomized crossover trial in 30 healthy men and women who received a control, apple, spinach, or apple plus spinach meal on separate days. Spinach also raised other nitric oxide markers, improved flow-mediated dilatation of the brachial artery and lowered systolic pressure, but not diastolic. Apple and spinach together did not add up to more than each alone.
Eating at least 300 mg more nitrate a day from green leafy vegetables for 7 days did not change blood pressure or artery stiffness in people with high-normal pressure
Randomized crossover trial in 38 adults aged 30 to 70 with a systolic pressure of 120 to 139 mm Hg. Nitrate and nitrite in saliva and blood rose at least fourfold, but ambulatory, home and office pressure and artery stiffness did not differ from the low-nitrate diet. It tested leafy greens as a group, and the authors doubt it works as a short-term strategy for this group.
Eating 50 g of high-lutein spinach 5 times a week for 12 weeks raised blood lutein by 33% and the density of the eye’s macular pigment
Two groups of 10 volunteers ate either a high-lutein or a low-lutein spinach variety. Blood lutein rose 22% on the low-lutein spinach, which was not significant, and macular pigment density rose only in the high-lutein group (from 0.343 to 0.374 at one measuring point). Small groups, no non-spinach control group.
Eating spinach powder for 8 weeks did not change macular pigment in healthy volunteers
Pilot study in 52 people who got carrot juice or a lutein-rich spinach powder at random. Macular pigment and blood markers of inflammation and oxidation did not change. Among people eating the lutein-rich food, those whose blood lutein rose the most tended to gain more macular pigment (r = 0.40).
Whole-leaf spinach gave about 5% of the beta-carotene but 45% of the lutein that a supplement gave
Three-week trial with groups of 12 people eating whole-leaf, minced or liquefied spinach, or taking a carotenoid supplement. Breaking up the leaf raised beta-carotene absorption to 6.4% (minced) and 9.5% (liquefied) of the supplement, while lutein stayed at 45 to 55% whatever the form.
The lutein in spinach was absorbed no better than from supplements and less well than from lutein-enriched eggs
Crossover trial in 10 healthy men who took 6 mg of lutein for 9 days as a supplement, a lutein ester supplement, spinach or lutein-enriched eggs. Blood lutein was higher after eggs than after the other three, which did not differ from each other.
Eating spinach for 3 weeks raised blood folate, and minced or liquefied spinach raised it more than whole leaves
Controlled trial in 28 men and 42 women split into six groups, five of them eating whole-leaf, minced or liquefied spinach (one with added fiber) or taking a carotenoid supplement on top of a control diet. The blood folate response was higher for spinach than for the control diet, and higher for minced and liquefied than for whole leaves (P = 0.03). The carotenoid supplement had no effect.
People absorbed 5.1% of the calcium in spinach against 27.6% of the calcium in milk
Randomized crossover trial in 13 healthy adults using meals with 200 mg of isotope-labeled calcium. The spinach had a slight excess of oxalate over calcium, so nearly all of its calcium was likely bound. The authors conclude spinach calcium is much less available than milk calcium.
Adding oxalic acid to a kale meal did not change iron absorption (10.7% versus 11.5%)
Two randomized crossover isotope studies in 16 women, 13 of whom finished both, using wheat rolls with 150 g of spinach, 150 g of kale, or kale plus potassium oxalate. Iron absorption from the spinach meal was 24% lower than from the kale meal, but not significantly so. The authors say oxalic acid in vegetables matters little for iron.
Only about 1.9% of the soluble oxalate in grilled spinach was absorbed over 24 hours, and dairy lowered it further
Randomized trial in 10 volunteers who ate 100 g of grilled frozen spinach alone or with cottage cheese, sour cream, sour cream plus milk, or olive oil. The spinach held 736.6 mg of soluble oxalate per 100 g. Sour cream and milk cut the amount absorbed significantly. Small trial, one type of spinach.
A single 5 g dose of spinach thylakoid extract reduced hunger and longing for food over 2 hours in overweight people
Double-blind crossover trial in 60 overweight or obese people. Compared with placebo, the extract (membranes from spinach leaves) did not change plasma lipids or energy eaten at dinner, and blood glucose after lunch was higher. It was a concentrated extract, not spinach leaves.
A thylakoid-rich spinach extract before breakfast reduced hunger by 21% and cravings for sweets by 38% in overweight women
Randomized placebo-controlled trial of a single dose. Satiety rose 14%, but food intake was not significantly changed. Like the study above, it used a concentrated extract and measured feelings, not weight.
About 200 g a day of vitamin K-rich leafy greens for 4 weeks lowered undercarboxylated osteocalcin by 31%, a blood marker tied to vitamin K use in bone
Randomized crossover trial in 30 adults (average age 62) with greens giving 164 µg a day of vitamin K1. Total osteocalcin fell 14% and the ratio of undercarboxylated to total osteocalcin 19% compared with control. It measured blood markers, not fractures, and tested leafy greens as a group.
Eating spinach 8 or more times a month went with a 30% higher risk of kidney stones in men and a 34% higher risk in older women, compared with less than once a month
Three US cohorts of 45,985 men, 92,872 older women and 101,824 younger women, with 4,605 stones over 44 combined years of follow-up. Spinach supplied more than 40% of the oxalate people ate, and it was not linked to stones in younger women. The authors say the data do not make dietary oxalate a major risk factor.
People who ate spinach or collard greens more often had a substantially lower risk of advanced macular degeneration
Case-control study of 356 people with advanced disease and 520 controls aged 55 to 80. The top fifth for carotenoid intake had a 43% lower risk (odds ratio 0.57), and lutein and zeaxanthin were the carotenoids most strongly linked. Diet was self-reported, and a link cannot prove cause.
About 1.3 servings a day of green leafy vegetables went with slower decline in thinking skills, equal to being 11 years younger
Prospective study of 960 people aged 58 to 99 who were followed for an average of 4.7 years. Higher intakes of vitamin K, lutein, nitrate, folate, kaempferol and alpha-tocopherol were each linked to slower decline, but beta-carotene was not clearly linked. It covered leafy greens as a group and cannot show cause.
Eating 1.45 or more servings a day of green leafy vegetables went with an 18% lower risk of open-angle glaucoma than 0.31 servings a day
Two US cohorts of 63,893 women and 41,094 men followed for up to 28 years, with 1,483 glaucoma cases. People in the top fifth for dietary nitrate had a 21% lower risk (rate ratio 0.79), and leafy greens made up 56.7% of the variation in nitrate intake. It cannot show that nitrate itself is the reason.
Eating more vegetables, with green leafy ones among the best, went with a 6% lower risk of cardiovascular disease
Meta-analysis of 81 cohorts with 4,031,896 people and 125,112 cardiovascular events. The risk ratio for vegetables was 0.94 for cardiovascular disease and 0.88 for stroke. Green leafy vegetables were among the sources with the greatest benefit, none showed harm, and the certainty of the evidence ranged from very low to moderate.
Higher dietary lutein and zeaxanthin went with a 26% lower risk of late macular degeneration but not of early disease
Meta-analysis of 6 cohort studies. The risk ratio for late disease was 0.74 (95% confidence interval 0.57 to 0.97) and for the wet form 0.68, while early disease showed 0.96, no real change. The authors say more studies are needed.
More green leafy vegetables went with a 14% lower risk of type 2 diabetes, while other vegetables and fruit showed no clear benefit
Meta-analysis of 6 cohort studies, 4 of which reported green leafy vegetables separately (hazard ratio 0.86, 95% confidence interval 0.77 to 0.97). The authors say leafy greens should be investigated further.
In 45,411 Singapore Chinese adults, dark green leafy vegetables were not clearly linked to type 2 diabetes (hazard ratio 1.05)
There were 5,207 new cases over 494,741 person-years. An updated meta-analysis of 11 studies with 754,729 people found a borderline link for green leafy vegetables (risk ratio 0.91, 95% confidence interval 0.84 to 1.00) with moderate-to-high heterogeneity, and the authors call the evidence not convincing.
In a human gut-cell model, lutein from spinach was taken up best from raw spinach rather than boiled or microwaved, whether fresh, frozen or canned
Lab study using simulated digestion and Caco-2 intestinal cells. Cooking did not change how well lutein went into micelles, the packages that carry it to the gut lining, but the cells took up less of it. This was a cell model, not people.
Rats fed spinach thylakoids for 10 days ate less food and had lower insulin after a glucose test
Rats on a thylakoid-enriched diet were compared with rats on a control diet. Blood glucose did not differ, and the thylakoid rats had more lactobacilli on the lining of the lower small intestine. Thylakoids are leaf membranes; this was an animal study.
Fats from spinach leaf membranes blocked inflammation signals in human vein cells exposed to a bacterial toxin
Lab study on cultured human umbilical vein cells. The spinach glycolipids lowered several inflammation markers and monocyte sticking, and raised nitric oxide production. Cells in a dish say nothing yet about what eating spinach does.
A water extract of spinach leaves eased gut damage in mice and rats with chemically induced colitis
Three animal models, with doses of 250 to 1,000 mg/kg. The extract reduced diarrhea and lesions in all three, most at the top dose, and the authors credit its flavonoids. It was an extract in animals, not spinach eaten by people.
Who should be careful with spinach
Most people can eat spinach freely. Take a little care if one of these applies:
- Warfarin. Raw spinach has 483 µg of vitamin K per 100 g, and vitamin K can change how this blood thinner works. You do not need to avoid it; keep the amount steady from week to week and check with your clinic before big changes.
- Kidney stones. Spinach is high in oxalate, and in three US cohorts eating it 8 or more times a month went with a 30% higher stone risk in men and 34% in older women. If you have had calcium oxalate stones, ask your doctor or dietitian.
- Relying on it for iron or calcium. Only 5.1% of the calcium in spinach was absorbed in one trial, and in people with no iron stores about 5 to 12% of iron is absorbed on vegetarian diets against 14 to 18% on mixed diets. Spinach helps, but pair it with other sources.
How to choose, store and eat spinach
- Raw: in a human gut-cell model, lutein was taken up best from uncooked spinach, whether it was fresh, frozen or canned.
- Boiled: boiling cut soluble oxalate in vegetables by 30 to 87% in a lab test, and the oxalate ended up in the cooking water, so pour it off.
- With fat or dairy: in 7 people eating a salad that included spinach, almost no carotenoids were absorbed with fat-free dressing and far more with a dressing made with 28 g of oil, and dairy lowered oxalate absorption from grilled spinach.
Choose spinach with fresh green leaves and skip limp, damaged or spotted bunches. Wrap it loosely in a damp paper towel in a bag, keep it in the fridge for up to five days, and rinse it just before use. In USDA tests of 707 spinach samples in 2016, 16 had a residue above the legal limit, the most of any food tested that year. The lab washed the samples first, so rinse leaves before eating.
Sources
- Dietary advice for patients taking warfarin. Cambridge University Hospitals NHS Foundation Trust.
- Anticoagulant medicines: considerations. NHS.
- Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr. 2010.
- Makkapati S, D’Agati VD, Balsam L. “Green smoothie cleanse” causing acute oxalate nephropathy. Am J Kidney Dis. 2018.
- Noonan SC, Savage GP. Oxalate content of foods and its effect on humans. Asia Pac J Clin Nutr. 1999.
- Chai W, Liebman M. Effect of different cooking methods on vegetable oxalate content. J Agric Food Chem. 2005.
- Brown MJ, Ferruzzi MG, Nguyen ML, et al. Carotenoid bioavailability is higher from salads ingested with full-fat than with fat-reduced salad dressings as measured with electrochemical detection. Am J Clin Nutr. 2004.
- Spinach. University of Nebraska-Lincoln Extension.
- Pesticide Data Program annual summary, calendar year 2016. USDA Agricultural Marketing Service.
History of spinach
Spinach, Spinacia oleracea, carries its route in its name. The English word came through Old French and Andalusian Arabic from the Persian aspānāḵ. A 2017 genome study of 120 spinach lines found that a wild species, Spinacia turkestanica, is likely the direct ancestor of the cultivated plant.
From there it spread along trade routes. Chinese records say spinach reached the Tang court from Nepal in the 7th century. Arabs are said to have brought it to Sicily in 827, and by the late 12th century it was grown in Spain, where the agricultural writer Ibn al-ʻAwwām called it the chieftain of leafy greens. It reached England and France in the 14th century, and the English cookbook The Forme of Cury, from 1390, calls it spinnedge.
Popeye first appeared on January 17, 1929, in E. C. Segar’s comic strip Thimble Theatre. His strength was first tied to spinach in 1931, and the animated cartoons later made canned spinach his trademark. A 2005 history of American child nutrition argues that the link between spinach and strength grew out of 1920s campaigns against child malnutrition.
The iron story has a history of its own. The earliest source one researcher found is a 1972 lecture saying spinach’s fame might have grown from a misplaced decimal point. A 1981 BMJ article by the hematologist Terence Hamblin spread the tale widely, and when asked later he could not recall where he had read it. The 2014 paper found no evidence that the error ever happened, and it reports the view that old iron figures were inflated by sample contamination or by mixing up fresh and dried spinach.
Spinach also has a food-safety chapter. In August and September 2006 an E. coli O157:H7 outbreak across several US states was linked to packaged spinach, and in Wisconsin eating spinach was strongly tied to illness before a voluntary recall. Today China grows about 92% of the world’s spinach, around 31 million tonnes in 2024 according to FAO data.
Sources
- Xu C, Jiao C, Sun H, et al. Draft genome of spinach and transcriptome diversity of 120 Spinacia accessions. Nat Commun. 2017.
- Rekdal OB. Academic urban legends. Soc Stud Sci. 2014. Full text.
- Hamblin TJ. Fake. Br Med J (Clin Res Ed). 1981.
- Lovett L. The Popeye principle: selling child health in the first nutrition crisis. J Health Polit Policy Law. 2005.
- Wendel AM, Johnson DH, Sharapov U, et al. Multistate outbreak of Escherichia coli O157:H7 infection associated with consumption of packaged spinach, August-September 2006: the Wisconsin investigation. Clin Infect Dis. 2009.
- Spinach. Wikipedia.
- Popeye. Wikipedia.
- When Nepal gifted spinach to China. The Kathmandu Post. 2023.
Frequently asked questions about spinach
Is spinach good for you?
For most people, yes. Raw spinach has 23 calories per 100 g and gives 402% of the Daily Value for vitamin K, 49% for folate and 52% for vitamin A. Large cohorts link green leafy vegetables to slower mental decline and a lower risk of glaucoma, but those are links, not proof, and no spinach finding here reaches strong evidence.
Does spinach have a lot of iron?
Not unusually. Raw spinach has 2.7 mg of iron per 100 g, 15% of the Daily Value, and the decimal point error behind the myth was never shown to have happened. It is plant iron, and in people with no iron stores about 5 to 12% of iron is absorbed on vegetarian diets against 14 to 18% on mixed diets. In 16 women, iron absorption from a spinach meal was 24% lower than from a kale meal, though not significantly.
Is raw or cooked spinach healthier?
Neither is clearly better. Lutein was taken up best from raw spinach in a gut-cell model, but in people, mincing or liquefying the leaves raised beta-carotene absorption from 5.1% to 9.5% of a supplement’s and raised blood folate more than whole leaves did. Boiling also cut soluble oxalate in vegetables by 30 to 87% in a lab test.
How much spinach should you eat a day?
No study here sets an ideal amount. Trials used 50 g five times a week for 12 weeks and a soup with 845 mg of nitrate a day for 7 days, and cohorts linked about 1.3 servings a day of green leafy vegetables to slower mental decline. One cup of raw spinach (30 g) has 7 calories and 121% of the Daily Value for vitamin K, so keep the amount steady if you take warfarin.
Can you eat too much spinach?
It is possible if you are prone to kidney stones. Frozen spinach had 736.6 mg of soluble oxalate per 100 g in one test, and in three US cohorts eating it 8 or more times a month went with 30% more stones in men and 34% in older women, but not in younger women. A case report linked a juice cleanse of oxalate-rich greens to kidney failure in a woman with other risk factors. For most people the risk is small, and eating spinach with dairy lowered oxalate absorption in a small trial.
Is spinach high in protein?
Not high, but it has some. Raw spinach has 2.9 g of protein per 100 g, or 0.9 g in a cup (30 g), which is close to half of its 23 calories. It scores 100 out of 100 for essential amino acids, so no essential amino acid is short.
Is spinach good for your eyes?
Possibly, through lutein, but the proof is thin. Spinach has 12,198 µg of lutein and zeaxanthin per 100 g, and eating it more often went with a lower risk of advanced macular degeneration in a case-control study. Yet a trial of 4,203 people found 10 mg of lutein plus 2 mg of zeaxanthin a day did not significantly cut progression, and 8 weeks of spinach powder did not change macular pigment in 52 healthy volunteers.
Does spinach help you lose weight?
No study here tested weight loss with spinach leaves. Spinach has 23 calories and 2.2 g of fiber per 100 g, so it fills a plate cheaply, but that is a swap effect, not a proven one. A spinach thylakoid extract reduced hunger in two small trials, though energy eaten did not change significantly, and it was a concentrated extract, not leaves.