Around the turn of the century, a group of general practitioners in Plymouth ran a trial that would struggle to get past an ethics committee today. Twenty-seven patients with osteoarthritis at the base of the thumb or index finger were asked to press a fresh stinging nettle leaf against the painful joint every day for a week, and to let it sting. Five weeks later, once the skin had settled, they did it again with a look-alike plant that does not sting, the white deadnettle, without being told which was which. Over the twelve weeks of the study the patients scored their pain and disability, and the week of real stings lowered both significantly more than the week of harmless ones [1].
It is a small study, and it measured pain, not cartilage. But it captures something a nutrition table cannot. Nettle is not a delicate herb. It defends itself with a chemical injection, it grows on ground people have disturbed and manured, it is cut with gloves and eaten with respect, and it has been doing so along Baltic farm edges for as long as there have been farms. Every September it does something easy to miss: the plants scythed in June come back as a second flush of young shoots, the last cut before frost. This article is about what is in those shoots, why they sting, and what the trials run in people can and cannot tell us.
A plant that follows people
Nettle grows where nitrogen is: around old farmsteads, along field edges, beside compost heaps and on the sites of houses that fell down a century ago. It is a marker of human settlement, and the relationship runs both ways, because for most of Baltic history nettle was food. A historical review of wild edible plants in Estonia, drawn from twenty-two ethnographic sources covering the 1770s to the 1960s and recording 147 plant species, places Urtica dioica among the most important species of all by diversity of use, alongside caraway and the wild berries [2]. The spring nettle soup of Latvia, Estonia and Lithuania is not a health fashion; it is what you ate in April when the cellar was down to its last cabbage and the first green thing in the yard was nettle.
Folklore also gave the plant a job. In the European herbal tradition nettle has been described since Dioscorides as a tonic, a diuretic and a "blood-purifier" [3]. We report that as folklore, because it is folklore: cleansing the blood is not something a plant does, and no trial has ever measured it. What the tradition was probably noticing is simpler. After a winter of grain, salt meat and stored roots, the first green leaves of the year bring vitamin A, calcium, protein and iron, and people felt better for eating them. The modern work has been to find out how much of each is really there.
What is actually in a leaf
The most careful composition study we have found is a 2013 paper from Virginia State University, in which Laban Rutto and colleagues harvested growing nettle shoots from field plots, separated the leaves, and analysed them raw, blanched and cooked [4]. The numbers are worth reading slowly, because they show how much the same plant varies with the season.
Raw autumn leaves were 89 per cent water and contained 3.7 g of protein, 278 mg of calcium and 1.2 mg of iron per 100 g. Raw spring leaves, from the first flush, were drier at 75 per cent water and contained 6.3 g of protein, 788 mg of calcium and 3.4 mg of iron per 100 g [4]. That is roughly a threefold difference in iron and calcium between two harvests of the same plot. For vitamin A the leaf is genuinely exceptional: the spring samples measured 11,403 IU per 100 g, most of it as beta-carotene, and the authors calculated that 100 g of processed nettle can supply 90 to 100 per cent of a day's vitamin A [4]. Then a surprise. Vitamin C in those samples measured only 0.5 to 1.1 mg per 100 g, close to nothing [4]. Older analyses summarised in the European Medicines Agency's monograph give 36 to 269 mg per 100 g [3], so either the vitamin C is highly variable or it is lost quickly after picking, or both. Either way, nettle is not a vitamin C plant you can rely on, which matters for what follows.
Dried, the leaf concentrates. A 2016 analysis of nettle leaf flour found 33.8 per cent crude protein, 9.1 per cent fibre and 16.2 per cent ash, the mineral fraction, on a dry-weight basis, with 3,497 micrograms of carotenoids per gram [5]. The European monograph gives 107 mg of iron per kilogram of dried leaf, notes that its calcium is more than three times that of peppermint leaf, and lists its carotenoids as lutein, beta-carotene, neoxanthin, violaxanthin and lycopene, with chlorophyll at 0.08 to 0.3 per cent of fresh weight [3]. It is a leafy green with the protein of a legume and the pigments of a carrot, and it grows in the ditch.
Iron is the hard part
Iron is the claim most often made for nettle, and the one that needs the most care. The iron in a leaf is non-haem iron, the plant form, and the body handles it very differently from the haem iron in meat. Richard Hurrell and Ines Egli, reviewing the isotope studies in 2010, put the bioavailability of dietary iron at 14 to 18 per cent for mixed diets and 5 to 12 per cent for vegetarian diets in people with no iron stores [6]. The background paper on iron for the 2023 Nordic Nutrition Recommendations notes that absorption from a given meal can range from under 2 to 50 per cent depending on the person's iron status and what else is on the plate [7]. What pushes it towards the low end is familiar: polyphenols, the tannins that make tea astringent, and phytate, the storage form of phosphorus in grains and seeds, both of which bind iron in the gut in a dose-dependent way [7][8].
What pushes it back up is ascorbic acid. Leif Hallberg's group in Gothenburg showed in 1989 that vitamin C in a meal counteracts the dose-dependent inhibition by phytate [8], and the Nordic paper summarises the wider literature the same way: ascorbic acid prevents the inhibitory effects of polyphenols and phytates on non-haem iron absorption [7]. This is well enough established that the European Union has written it into law. Under Regulation 432/2012 the authorised claim wordings include "Vitamin C increases iron absorption", "Iron contributes to normal formation of red blood cells and haemoglobin" and "Iron contributes to the reduction of tiredness and fatigue", each usable only on a food that is at least a source of the nutrient [9]. We wrote about the rest of that vitamin's work in Vitamin C: Beyond Immunity.
Two honest sentences follow. A bowl of nettle soup from spring leaves carries a useful amount of iron, a bowl from autumn leaves about a third as much, and in either case most of it will pass through unless there is vitamin C in the same meal. And we have not found a single clinical trial of nettle, as leaf, soup, tea or juice, for iron-deficiency anaemia. The plant's reputation as a blood-builder rests on its composition and on tradition, not on a study in people with low haemoglobin, and we would rather say so than imply otherwise.
The silica question
The second mineral in nettle's reputation is silica, and here the numbers are clearer than the meaning. The dried leaf contains 1 to 4 per cent silicon dioxide, part of it as water-soluble silicates, and silica appears again as 2.16 per cent of the ash [3]. Much of it is structural: it stiffens cell walls and forms the hardened, glass-like tip of the stinging hair, which is why the hair snaps cleanly when brushed. Whether the silicon in nettle is absorbed in a useful form, and whether it does anything for hair, nails or bone, has not been tested in a human trial we could find. Nettle is a rich source of silica in the analytical sense; that is as far as the evidence goes.
Why it stings
The sting is the most studied thing about nettle, and the story has changed in twenty years. Each stinging hair is a single elongated cell with a brittle silicified tip. Touch it and the tip breaks off along a preformed line, leaving a bevelled point like a hypodermic needle, and the pressure of your skin against the bulb at the base injects the contents. The classical account of those contents, repeated in the European monograph, is small amounts of histamine, acetylcholine, serotonin and formic acid, with some leukotrienes [3]. Histamine explains the wheal; acetylcholine and serotonin were assumed to explain the pain; formic acid, the ant's weapon, was the folk explanation for the burn.
In 2006 a Taiwanese group tested that account in a related species, Urtica thunbergiana, by washing the contents out of the hairs and separating them by chromatography [10]. The major constituents were histamine, oxalic acid and tartaric acid; serotonin and formic acid were present only at low concentration. Injected into rats, 2 per cent oxalic acid and 10 per cent tartaric acid produced persistent pain behaviour, while 10 per cent formic acid and 2 per cent serotonin produced only moderate pain for the first ten minutes, and histamine and acetylcholine produced no significant pain response at all [10]. The long, dull ache of a nettle sting is mostly two plant acids, not formic acid.
There is a third layer. In 2022 a team at the University of Queensland working on the New Zealand tree nettle, Urtica ferox, found that the persistent pain of its sting is driven by small neurotoxic and cytotoxic peptides acting on the sodium channels of sensory nerves [11]. The same group reported similar sequences in transcriptome data from ordinary Urtica dioica, and when a high-quality genome of the common nettle was published in 2025, the authors found two copies of a gene putatively encoding one of those peptides, urthionin, with an 86 per cent match to the tree-nettle toxin [12]. Our garden nettle carries a milder version of a real venom. All of it is disarmed by heat or drying: a minute in boiling water collapses the hairs and destroys the peptides, which is why soup, tea and blanched leaf have never hurt anyone, and why the Plymouth trial is the only study here in which the sting was the point.
What the blood sugar trials found
Set aside the folklore, and the best human evidence for nettle leaf is in a place the folklore never mentioned: blood sugar. In 2013 Saeed Kianbakht and colleagues in Tehran ran a randomised, double-blind, placebo-controlled trial in 92 patients with advanced type 2 diabetes already on conventional oral drugs. Half took a 500 mg capsule of nettle leaf extract every eight hours for three months; half took placebo. At the end, fasting glucose, two-hour post-meal glucose and HbA1c were all significantly lower in the nettle group, with p-values of less than 0.001, 0.009 and 0.006, and there was no effect on kidney or liver markers or on blood pressure [13].
One trial is one trial, so it helps that the question has since been pooled. A 2020 meta-analysis in Phytotherapy Research gathered eight randomised controlled trials of nettle supplementation in type 2 diabetes, 401 participants in all. Fasting blood glucose fell by a mean of 18 mg/dL against control, a real but modest change, while the reduction in HbA1c, 0.77 percentage points, did not reach statistical significance [14]. The authors concluded that nettle may help with fasting glucose and that better trials are needed. We would add that these were extract capsules taken alongside medication, not soup, and that 401 people across eight trials is a small literature for a plant this common.
Hay fever and the prostate, briefly
Two other trials are quoted so often that they belong here, mostly so that their size is on the record. In 1990 Paul Mittman in Oregon randomised 98 people with hay fever to 300 mg of freeze-dried nettle leaf or placebo; 69 finished, 31 on nettle and 38 on placebo. Of the nettle group, 58 per cent rated the treatment moderately or highly effective, against 37 per cent on placebo, a difference that reached significance on a global rating but was much smaller on the symptom diaries, and there was no objective measure at all [15]. It is a weak result from a small trial, and it has not been convincingly repeated. The other is a 2005 Iranian trial of nettle root, not leaf, in 620 men with symptoms of benign prostate enlargement over six months, in which 81 per cent of treated men reported improvement against 16 per cent on placebo, with a fall in symptom score and a modest fall in prostate volume [16]. That is a large study, but it concerns a root extract taken for a specific complaint, and it says nothing about the leaf in your soup.
What to do this week
September is the second flush, and the last one, so the practical advice starts outdoors.
Cut the young tops. With gloves and scissors, take the top four to six leaves of the regrowth since the summer cut; ignore anything that has flowered or seeded, which is stringy and bitter. A minute in boiling water takes out the sting entirely, and blanched leaf freezes well.
Make the soup the old way, plus one thing. Potato, onion, a handful of blanched nettle, stock, and sour cream at the end is the Baltic template. The addition the research argues for is vitamin C in the same meal, because that is what turns the leaf's non-haem iron into iron you can absorb [7][8][9]. A small glass of a sharp, vitamin C-rich juice alongside is the easiest way. Pure rosehip is the obvious partner; ours is Nordic Petal, and we told that fruit's story in The Wild Rose Secret. Sunthorn, 100% sea buckthorn, does the same job with a different flavour, and Go Berry, aronia with a quarter sea buckthorn, is the single-serve option if you want the berry polyphenols too.
If you would rather drink the leaf. We press nettle too. Evergreen is 100% organic cold-pressed nettle juice, nothing added, taken as a 50 ml measure before a meal, and it tastes exactly like what it is: green, herbal, slightly tart. With one of the juices above, it is the pairing this article has been describing. The Green Restart set puts Evergreen alongside aloe and celery root if you want the whole green shelf at once.
| Juice | What is in it | Best for |
|---|---|---|
| Evergreen | 100% organic cold-pressed nettle juice | The leaf itself, as a daily 50 ml measure when there is no fresh nettle to cut |
| Nordic Petal | 100% organic rosehip juice | The vitamin C partner for nettle soup or Evergreen; the most direct route to better iron absorption |
| Sunthorn | 100% organic sea buckthorn juice | Vitamin C with the berry's oils and carotenoids, for those who prefer sea buckthorn's sharper taste |
| Go Berry | 75% organic aronia, 25% organic sea buckthorn | A single-serve glass that brings vitamin C and aronia polyphenols to the same meal |
Keep the tea for what it is. Dried nettle makes a pleasant, faintly grassy infusion, and the European monograph accepts it as a traditional remedy for minor joint pain and for flushing the urinary tract [3]. It is not a meaningful source of iron; most of the minerals stay in the leaf. Drink it because you like it.
One line of caution: nettle is a mild diuretic and the extract trials ran alongside diabetes medication, so if you take water tablets, blood-pressure or blood-sugar drugs, have a word with your pharmacist before adding it daily.
Nettle, in short
Nettle leaf is rich in calcium, vitamin A as beta-carotene, protein and non-haem iron, though the iron varies about threefold with season. Plant iron is poorly absorbed without vitamin C in the same meal. Trials show extract capsules lower fasting glucose in type 2 diabetes; there are no trials of nettle for anaemia.
Back to the thumb
The Plymouth patients were asked to do something their grandmothers might have done without a protocol: press a nettle to a sore joint and let it burn. We now know more about the burn than they did. It is two plant acids and a small peptide toxin, injected through a silica needle, and it does the joint no harm. We also know more about the leaf. It is measurably one of the most nutrient-dense things growing in a Baltic ditch, most valuable in spring, still worth cutting in September, and best eaten with something sour beside it.
What we do not know is whether any of that shows up on a blood test in a person who eats nettle soup every week, because nobody has run the trial. The plant has fed people here for a very long time on the strength of ordinary observation. That is old Baltic sense, and it turns out to have been reasonably good chemistry.
Frequently asked questions
Is nettle a good source of iron?
It contains iron, but the amount varies: a 2013 analysis found 1.2 mg per 100 g in autumn leaves and 3.4 mg in spring leaves [4]. It is non-haem iron, absorbed at roughly 5 to 18 per cent depending on the meal [6], and vitamin C in the same meal raises absorption [7][9]. No trial has tested nettle for anaemia.
Does nettle lower blood sugar?
In a 2013 trial, 92 people with type 2 diabetes took 500 mg of nettle leaf extract three times a day for three months alongside their usual drugs; fasting glucose, post-meal glucose and HbA1c fell against placebo [13]. A meta-analysis of eight trials, 401 people, found fasting glucose fell by 18 mg/dL while HbA1c did not change significantly [14].
Why does a nettle sting hurt for so long?
The hair injects histamine, which makes the wheal, but the persistent ache comes mainly from oxalic and tartaric acid: in rat tests, 2 per cent oxalic and 10 per cent tartaric acid caused long-lasting pain while formic acid and serotonin did not [10]. Small neurotoxic peptides, first found in the tree nettle, add to it [11][12].
Does nettle help hay fever?
The evidence is thin. The only widely cited trial, from 1990, randomised 98 people to 300 mg of freeze-dried nettle or placebo; 69 finished, and 58 per cent on nettle rated it effective against 37 per cent on placebo, with no objective measures and a 30 per cent dropout [15]. It has not been convincingly repeated.
References
- Randall C, Randall H, Dobbs F, Hutton C, Sanders H. Randomized controlled trial of nettle sting for treatment of base-of-thumb pain. J R Soc Med. 2000;93(6):305–309. doi:10.1177/014107680009300607
- Kalle R, Sõukand R. Historical ethnobotanical review of wild edible plants of Estonia (1770s–1960s). Acta Soc Bot Pol. 2012;81(4):271–281. doi:10.5586/asbp.2012.033
- European Medicines Agency, Committee on Herbal Medicinal Products. Assessment report on Urtica dioica L., Urtica urens L., folium. EMA/HMPC/508013/2007. London; 14 January 2010.
- Rutto LK, Xu Y, Ramirez E, Brandt M. Mineral properties and dietary value of raw and processed stinging nettle (Urtica dioica L.). Int J Food Sci. 2013;2013:857120. doi:10.1155/2013/857120
- Adhikari BM, Bajracharya A, Shrestha AK. Comparison of nutritional properties of stinging nettle (Urtica dioica) flour with wheat and barley flours. Food Sci Nutr. 2016;4(1):119–124. doi:10.1002/fsn3.259
- Hurrell R, Egli I. Iron bioavailability and dietary reference values. Am J Clin Nutr. 2010;91(5):1461S–1467S. doi:10.3945/ajcn.2010.28674F
- Domellöf M, Sjöberg A. Iron – a background article for the Nordic Nutrition Recommendations 2023. Food Nutr Res. 2024;68:10451. doi:10.29219/fnr.v68.10451
- Hallberg L, Brune M, Rossander L. Iron absorption in man: ascorbic acid and dose-dependent inhibition by phytate. Am J Clin Nutr. 1989;49(1):140–144. doi:10.1093/ajcn/49.1.140
- Commission Regulation (EU) No 432/2012 of 16 May 2012 establishing a list of permitted health claims made on foods, other than those referring to the reduction of disease risk and to children's development and health. OJ L 136, 25.5.2012, p. 1–40.
- Fu HY, Chen SJ, Chen RF, Ding WH, Kuo-Huang LL, Huang RN. Identification of oxalic acid and tartaric acid as major persistent pain-inducing toxins in the stinging hairs of the nettle, Urtica thunbergiana. Ann Bot. 2006;98(1):57–65. doi:10.1093/aob/mcl089
- Xie J, Robinson SD, Gilding EK, et al. Neurotoxic and cytotoxic peptides underlie the painful stings of the tree nettle Urtica ferox. J Biol Chem. 2022;298(8):102218. doi:10.1016/j.jbc.2022.102218
- Hirabayashi K, Dumigan CR, Kučka M, et al. A high-quality phased genome assembly of stinging nettle (Urtica dioica ssp. dioica). Plants. 2025;14(1):124. doi:10.3390/plants14010124
- Kianbakht S, Khalighi-Sigaroodi F, Dabaghian FH. Improved glycemic control in patients with advanced type 2 diabetes mellitus taking Urtica dioica leaf extract: a randomized double-blind placebo-controlled clinical trial. Clin Lab. 2013;59(9–10):1071–1076. doi:10.7754/Clin.Lab.2012.121019
- Ziaei R, Foshati S, Hadi A, et al. The effect of nettle (Urtica dioica) supplementation on the glycemic control of patients with type 2 diabetes mellitus: a systematic review and meta-analysis. Phytother Res. 2020;34(2):282–294. doi:10.1002/ptr.6535
- Mittman P. Randomized, double-blind study of freeze-dried Urtica dioica in the treatment of allergic rhinitis. Planta Med. 1990;56(1):44–47. doi:10.1055/s-2006-960881
- Safarinejad MR. Urtica dioica for treatment of benign prostatic hyperplasia: a prospective, randomized, double-blind, placebo-controlled, crossover study. J Herb Pharmacother. 2005;5(4):1–11. doi:10.1080/J157v05n04_01
This article is educational and is not medical advice. If you are pregnant, breastfeeding, taking prescribed medication or managing a diagnosed condition, speak to your doctor or pharmacist before making changes.
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