Editor’s Note: Each month, HerbalEGram highlights a conventional food and
briefly explores its history, traditional uses, nutritional profile, and modern
medicinal research. With each article, we also feature a nutritious recipe for
an easy-to-prepare dish to encourage readers to experience the extensive
benefits of these whole foods. With this series, we hope our readers will gain
a new appreciation for the foods they see at the supermarket and frequently
include in their diets.
The basic materials for this series were compiled
through the American Botanical Council’s (ABC’s) Dietetic Internship Program. We would like to acknowledge ABC Chief Science Officer
Stefan Gafner, PhD, for his contributions to this project.
By Hannah
Baumana and Jenny Perezb
a HerbalGram Associate Editor
b ABC Education
Coordinator
Overview
Urtica dioica (Urticaceae) is
commonly known as nettle, common nettle, or stinging nettle. The species is an
herbaceous perennial with a spreading growth habit. Growing 4-6 feet tall,
stinging nettle produces numerous erect and wiry stems that hold up its
opposite, roughly textured, serrated leaves.1-4 It produces small,
inconspicuous greenish-brownish flowers that emerge as axillary inflorescences.2
The stems and undersides of leaves are covered with hairs called
trichomes. When touched, these stinging trichomes inject a chemical cocktail
that typically causes localized skin irritation as well as a painful, tingling
sting from which the species has derived its most common name, stinging nettle.1,5
The
Urticaceae family contains about 500 known species, distributed mainly in tropical
areas.1 The genus Urtica, whose
name comes from the Latin uro (to
burn) and urere (to sting), consists
of both annual and perennial herbaceous plants known for the burning properties
of the stinging hairs of their leaves and stems.1,2,6 (Nettle
is the Anglo-Saxon word for “needle.”) Urtica
urentissima, a species found in Java, produces burning effects that can
last an entire year and reportedly can even cause death. Urtica dioica is, comparatively, a more docile species that has a
long history of use as a food and medicine.1,2,7 It is widely
distributed in temperate climates of Europe, Asia, northern Africa, and North
America.1 In North America, U.
dioica has become naturalized in every state except Hawaii.1 There
are at least six subspecies of U. dioica,
some of which formerly were classified as separate Urtica species. Urtica dioica
subsp. galeopsifolia is the only one
of the six subspecies that does not have stinging hairs.1
Phytochemicals and Constituents
Stinging
nettle is a perennial edible whose leaves are a relatively good source of
caloric energy, protein, fiber, and an array of health-promoting bioactive
compounds.7 These include vitamins A, C, and K; fatty acids
(α-linoleic acid and linoleic acid); and minerals including iron, manganese,
potassium, and calcium.2,7,8 Notably, stinging nettle leaves contain
nine carotenoids, including lutein and lutein isomers, β-carotene, and
β-carotene isomers.2 Other phytochemicals in nettle leaf include B
vitamins, vitamin E, coumarins, flavonoids, phenolic acids, tannins, organic
acids, water-soluble silicates, and chlorophyll.8,9 The therapeutic
benefit of stinging nettle is attributed to its abundant phenolic compound
content, which includes caffeic acid, ferulic acid, esculetin, scopoletin, kaempferol,
quercetin, quercitrin, rutin, and glycoproteins.2 Stinging nettle
leaves can be cooked like spinach (Spinacia
oleracea, Chenopodiaceae) and are safe for consumption, as heat deactivates
the stinging compounds.10 Nettle leaf has higher levels of all
essential amino acids, except leucine and lysine, than spinach.11
When
harvested at a length of four to six inches, young nettle leaves are most
tender, sting less, and are higher in iron and manganese than mature leaves.5
However, nettle plants that are two years old or more contain higher levels of
chlorophyll and carotenoids than younger plants. Young leaves harvested in
early spring also can be dried for use in teas, soups, and baked goods. Nettle
leaf retains a significant portion of vitamins, minerals, and essential nutrients
even after leaves are blanched or cooked/boiled prior to freezer storage. To
prepare a nettle infusion that retains the highest level of vitamin C, a study
confirmed that the most efficient steeping time is 10 minutes at a temperature
of 140°F (60°C).8 Further consideration should be given to the
processing and selling of stinging nettle leaf as a functional and nutritive
food.
Historical and Commercial Uses
Some
consider stinging nettle a bothersome weed, but its long history of use tells a
different story. Stinging nettle has been used as a source of fiber (stem), dye
(leaf and rhizome), food/fodder (leaf), and medicine (leaf, rhizome/root, and
seed).2,8
Since
ancient times, stinging nettle has been used as a fiber crop substitute for
flax (Linum usitatissimum, Linaceae).
In Denmark, burial shrouds made from nettle fiber were discovered that date
back to the Bronze Age (3000–2000 BCE). Early Europeans and indigenous
Americans used the strong nettle fiber to make sailcloth, sackcloth,
cordage/rope, and fishing nets.1 In Scotland, nettle stalk was
cultivated for fiber and also used for small-scale papermaking. Nettle fiber
also was used during both World Wars when other crops like cotton (Gossypium hirsutum, Malvaceae) were scarce.
Stinging nettle fiber has a cellulose content similar to that of flax and hemp
(Cannabis spp., Cannabaceae), and it
is much stronger than both flax and cotton, while being comparable in strength
to ramie (Boehmeria nivea,
Urticaceae) fiber.12
In
periods of food shortage during both World Wars, stinging nettle was used
fresh, dried, milled, or as silage for feeding poultry, cattle, horses, and
pigs.12 Ranchers used nettle in livestock feed as a nutritious way
to supplement the animals’ diets. By adding stinging nettle leaf into poultry
feed, vitamin A intake increased by about 60-70% and protein intake by about 15-20%,
reducing overall feeding requirements by about 30%. Hens supplemented with
nettle feed typically lay eggs with brighter yellow carotenoid-rich yolks.12
Considered
a nutritive food and medicine for thousands of years among numerous cultures,
stinging nettle leaves have been used traditionally for scurvy, anemia,
arthritis, seasonal allergies, wound healing, and general fatigue, and as a
diuretic and to stimulate pancreatic secretion.1,9 Stinging nettle
tea has been used historically as a cleansing spring tonic and blood purifier.1,3
The juice of nettle leaf has been used as a hair rinse to control dandruff and
to stimulate hair growth, and is a functional ingredient in modern European
hair-care formulations. It is used as a vegetarian source of rennet in
cheese-making and is still included among Passover herbs.1
Nettle
leaf has been used safely in large food-like doses (up to 100g daily) for
thousands of years.5 Ancient Egyptians reportedly used nettle
infusions to relieve arthritis and lower back pain.7 Hippocrates
(460-ca. 377 BCE) and other early Greek physicians used nettle for more than 60
ailments. In the first and second centuries CE, Greek physicians Dioscorides
and Galen reported the use of stinging nettle leaf for its diuretic and
laxative properties and for the treatment of asthma, pleurisy, and spleen
illnesses.3 The 16th-century herbalist John Gerard used nettle leaf
as an antidote for poison.1 In the 19th century, the classification
of stinging nettle as a diuretic was documented in Greek medical literature.5
It is
thought that nettle leaf’s high chlorophyll content gives it detoxifying and anti-infective
properties. In his 2nd-century book De
Simplicibus Medicaminibus, Galen
recommended nettle for dog bites, gangrenous wounds, swellings, nosebleeds,
mouth sores, and tinea (fungal infections caused by ringworm). Seventeenth-century
English herbalist Nicholas Culpeper recommended a nettle-honey preparation for wounds
and skin infections, worms in children, as an antidote to venomous stings, and as
a gargle for throat and mouth infections.1 Modern research on
chlorophyll indicates that it has some detoxifying, anti-carcinogenic
properties and may ameliorate the side effects of some drugs.2 Nettle
leaves also are used as a source of chlorophyll for commercial supplements.13
Additionally, nettle’s vitamin K-rich leaves were powdered and used as a
styptic for nosebleeds, and used internally for excessive menstruation, and
internal bleeding.1,3
The
season for nettle leaf medicine is spring, when it traditionally is harvested
and used fresh or dried for its ability to deliver bountiful nutrients.1
Many North American tribes consider nettle tea safe and appropriate to use as a
gynecological aid for those with anemia or malnourishment.1
Stinging
nettle is a very popular wild edible plant (WEP) in several developing
countries, where it is used in soups, curries, or as a cooked vegetable. Vinegar
or lemon (Citrus limon, Rutaceae) juice often is added to cooked nettle
preparations to improve flavor and enhance mineral absorption.14 In the
Caucasus country of Georgia, a meal of boiled nettle greens seasoned with
walnuts (Juglans spp., Juglandaceae) is
common. In many cases, these WEPs contribute to community food security and,
potentially, to local economies.7
Nettle
leaf powder/flour has been incorporated into breads and pastas and is used as a
protein-rich supplement in starchy diets. In one analysis, the protein content
of ground wheat (Triticum aestivum,
Poaceae), barley (Hordeum vulgare,
Poaceae), and stinging nettle was found to be 10.6%, 11.8%, and 33.8%,
respectively, indicating that the nettle powder contained about three times more
protein per serving than the cereal crops. 7
A low-carbohydrate,
high-fiber diet can support good digestive health. Nettle powder has low
carbohydrate content with high levels of protein, minerals, fat, and fiber.
Nettle powder is considered a low-glycemic food. Whole grains alone can provide
much needed fiber to the diet. However, grain products enriched with nettle
powder can provide extra fiber, in addition to an array of healthful nutrients.
When combining nettle powder with barley flour into items like biscuits,
noodles, and breakfast cereals, the protein, mineral, fiber, and bioactive
compound content increased while overall caloric value decreased, according to
an analysis. 7
A practice
called “urtification” is perhaps the most ancient medicinal use of the plant. In
this process, fresh nettle, with its stinging compounds, was applied externally
as a rubefacient to stimulate circulation and bring warmth to joints and
extremities of paralytic, rheumatic, or stiff limbs.5,7 This induced,
localized irritation stimulates an immune response and pain relief after the
stinging subsides. This was considered standard practice for treating chronic
rheumatism, lethargy, coma, paralysis, and even typhus and cholera.1,5
Ironically, nettle leaves often were prepared as syrup or tincture to treat
urticaria, or the rash they produce upon contact with the skin.1
The
root of stinging nettle is a rich source of phytosterols and has been used to
reduce prostate gland inflammation and to treat rheumatic gout, nettle rash,
and chickenpox.3,10 In 1986, the German Commission E approved the
use of stinging nettle root, taken orally, as a nonprescription medicine to
treat urinary difficulties associated with stages I and II of Benign Prostatic
Hyperplasia (BPH).14,15 The European Medicines Agency’s 2012 monograph
on nettle root indicates its safe use to relieve lower urinary tract symptoms
(LUTS) related to BPH.16
Modern Research
Based
on published evidence, U. dioica and
its phytoconstituents have both hypoglycemic and anti-inflammatory activities.3
Nettle leaf, whether used orally or topically, has been shown to be able to inhibit
pro-inflammatory enzymes.2 This indicates that nettle leaf may be a
potential aid in treating chronic, inflammatory disease processes. Promising
evidence suggests that nettle can help control inflammation associated with
diabetes mellitus, rheumatoid and osteoarthritis, allergic rhinitis (hay fever),
and BPH.12
Diabetes Mellitus
Type
2 diabetes mellitus has become one of the most common preventable diseases
globally. Hyperglycemia, the relative or absolute deficiency of insulin at the
cellular level, is one of the predisposing factors for oxidative stress in the
body.17 Oxidative stress — often indicated by elevated levels of low-density lipoprotein (LDL) cholesterol and glutamic pyruvic transaminase (SGPT), and low levels
of nitric oxide — increases the incidence of cardiovascular risk factors and
contributes to diabetic macro- and micro-vascular complications. Moreover, high
blood glucose causes fat deposits in the liver. Stinging nettle leaf extracts have demonstrated natriuretic
(stimulating sodium excretion via urine), diuretic, and hypotensive effects.
Nettle leaf offers a therapeutic dietary option for patients with digestive and
kidney diseases or injuries after renal transplantation, as well as those with
diabetes.2
Stinging
nettle leaf extract acts on the pancreas to increase insulin secretion by the
Islets of Langerhans and has an inhibitory effect on alpha-glucosidase.
Theoretically, stinging nettle leaf extract’s polyphenols may protect beta
cells in the pancreas and stabilize lipid peroxidation.17 Its
effects on blood pressure are tied directly to stinging nettle’s ability to
increase serum nitric oxide levels, which opens potassium channels and has relaxant
effects on blood vessel walls.
A
2015 clinical study found that supplementation with U. dioica hydroethanolic aerial parts extract for eight weeks helped
improve markers of cardiovascular disease and oxidative stress in diabetic
patients.17 At the end of the study, participants in the nettle
extract group experienced a statistically significant reduction in fasting
blood glucose, lower triglyceride levels, increased high-density lipoprotein (HDL)
cholesterol levels, decreased SGPT levels, increased nitric oxide levels, and
increased superoxide dismutase (SOD) over baseline, indicating an overall
reduction in oxidative stress. The only change in the placebo group was an
increase in triglyceride levels. Researchers suggest these results encourage
the use of U. dioica as an additional
therapy in those with type 2 diabetes.
Rheumatoid Arthritis and Osteoarthritis
According
to the US Centers for Disease Control and Prevention (CDC), the most common
form of arthritis is osteoarthritis. Other common rheumatic conditions include
gout, fibromyalgia, and rheumatoid arthritis.18 In clinical trials
that tested the effectiveness of nettle extract or capsules against the common
NSAID diclofenac for the treatment of rheumatoid arthritis, osteoarthritis, and
fibromyalgia, stinging nettle preparations alone provided moderate pain relief and
had fewer side effects than diclofenac.5 The use of stinging nettle
in addition to diclofenac provided the greatest amount of pain relief, and
subjects used lower doses of diclofenac to achieve pain relief.
The
use of fresh nettle topically to control pain and inflammation works in the
same manner as topical capsaicin cream: the histamine released upon contact
causes a counterirritant effect resulting in localized irritation that blocks
afferent sensory nerves from carrying pain signals away from the area of
urtication.5,19 Three different clinical trials have investigated topical
nettle leaf application for the treatment of pain associated with
osteoarthritis. Participants in these trials reported a significant reduction
in pain as well as the use of NSAIDs for pain management.5 Other
studies have investigated pain relief with a cream from a stinging nettle
extract in an oil-in-water emulsion, a more practical way to integrate modified
“urtification” treatment in a clinical setting.19
One
small clinical study with 23 osteoarthritis patients used nettle cream topically
twice daily for two weeks. After the study concluded, not only was there a mean
reduction in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC)
scores for those using the stinging nettle leaf cream, but many of the
participants requested continuance of the nettle cream treatment to alleviate
pain and improve physical function.19
Allergic Rhinitis
Allergic
rhinitis, or seasonal allergies, is a major risk factor for developing asthma.20
Common over-the-counter (OTC) drugs for seasonal allergy symptoms often are
associated with adverse side effects, including drowsiness, dry mouth, and headache.
Freeze-dried stinging nettle leaves have been used to treat symptoms of
allergic rhinitis. Freezing the fresh leaves or their extracts preserves the
bioactive amines including histamine and acetylcholine.5 Nettle leaf
prevents the release of pro-inflammatory mediators that cause allergic symptoms
such as sneezing, nasal congestion, or itchy, watery eyes.2
In a
clinical trial, patients with seasonal allergies received 300 mg of
freeze-dried stinging nettle root extract daily for one week. Subjects in this
trial rated the nettle preparation’s effectiveness higher than placebo and
previous allergy medications.5 However, outcomes of a 2017 clinical
trial using freeze-dried nettle root (a proprietary product commercially known
as Urtidin [Barij Essence Pharmaceutical Co.; Kashan, Iran]) for seasonal
allergy relief showed only a small improvement in the treatment group, who
received Urtidin (one 150-mg tablet given four times daily; 600mg total) in
addition to 10 mg loratadine (a common antihistamine) and nasal saline rinses
over a one-month period.20 Despite the safety profile and low
toxicity associated with the use of freeze-dried nettle root, additional,
higher quality clinical trials are needed to further assess the efficacy of freeze-dried
nettle preparations to relieve symptoms associated with seasonal allergies.
Benign Prostatic Hyperplasia
BPH
is a common condition that occurs in aging men and eventually leads to LUTS, such
as pain and difficulty with urination, urine storage, and post-urination (post-micturition)
symptoms including dribbling and feeling of incomplete emptying.21 Standard
medical treatments for LUTS include α1-blockers and 5α-reductase inhibitors,
but both have undesirable side effects (postural hypotension and sexual
dysfunction, respectively).
There
is growing evidence that stinging nettle root is a safe and effective treatment
for BPH.21 A 2016 meta-analysis of the clinical use of stinging
nettle root extract for LUTS and BPH confirm that daily doses of 300-600 mg of
stinging nettle root were superior to active controls (i.e., α1-blocker and
5α-reductase inhibitor pharmaceutical drugs). No randomized controlled trials evaluated
reported any serious adverse side effects in patients who received stinging
nettle root extract.
Consumer Considerations
The
use of stinging nettle leaf as a vegetable poses some challenges. The main challenge
is urticaria: the immediate burning, stinging sensation upon contact with
nettle leaves, which is followed by a short-lived, blanching rash.4 Those
harvesting fresh nettle leaves must be cautious and avoid direct skin contact
by wearing long sleeves and gloves. Once harvested, leaves should be cooked or
steamed for 10-15 minutes before ingesting to deactivate nettle’s stinging
compounds.14 The mechanism of action behind nettle’s sting is both
biochemical and mechanical. Biochemically, nettle hairs release histamine,
serotonin, acetylcholine, and leukotrienes B4 and C4. Mechanical irritation is
induced when some of the trichomes remain in the skin after contact with the
stems or leaves.4 For fresh nettle rash or stings, a poultice of the
leaves of dock (Rumex spp.,
Polygonaceae), which generally grows near nettle patches, is a traditional
remedy.1
An
additional concern is the plant’s ability to bioaccumulate minerals like
chromium, as well as heavy metals like arsenic and lead.22 Nettle
patches are common on farmlands and orchards where soils may have been treated by
agricultural pollutants, which make them contaminated substrates for plants
like stinging nettle. Studies on stinging nettle leaf grown in contaminated
orchard soils indicated significantly higher concentrations of arsenic and lead
than those harvested from wild stands. Based on these findings, soils need to
be tested for heavy metals and other contaminants prior to commercial
cultivation and production of stinging nettle leaves. This will help to ensure
stinging nettle grown for food and medicine maintains its quality and safety.
Nutrient Profile23
Macronutrient Profile: (Per 1 cup stinging
nettle leaves, blanched [approx. 89 grams])
37 calories
2.4 g
protein
6.7 g
carbohydrate
0.1 g
fat
Secondary Metabolites: (Per 1 cup stinging
nettle leaves, blanched [approx. 89 grams])
Excellent source of:
Vitamin
K: 443.8 mcg (369.8% DV)
Vitamin
C: 243 mg (270% DV)
Vitamin
A: 1790 IU (35.8% DV)
Calcium:
428 mg (32.9% DV)
Manganese:
0.7 mg (30.4% DV)
Dietary
Fiber: 6.1 g (20.3% DV)
Very good source of:
Magnesium:
51 mg (12.1% DV)
Riboflavin:
0.14 mg (10.8% DV)
Iron:
1.5 mg (8.3% DV)
Potassium:
297 mg (6.3% DV)
Vitamin
B6: 0.09 mg (5.3% DV)
Phosphorus:
63 mg (5% DV)
Also provides:
Folate:
14 mcg (3.5% DV)
Niacin:
0.35 mg (2.2% DV)
Trace amounts:
Thiamin:
0.01 mg (0.8% DV)
DV =
Daily Value as established by the US Food and Drug Administration, based on a
2,000-calorie diet.
Recipe: Stinging
Nettle Spanakopita
Adapted from Jen
Farr24
Wear gloves while handling raw, fresh
nettle leaves and stems. Wash leaves in cool water, then dry thoroughly.
Check the source website for a photo tutorial on preparing the phyllo
packets.
Ingredients:
- 6
sheets frozen phyllo pastry, thawed
- 2
teaspoons melted butter
- 2
tablespoons extra virgin olive oil
- 2
cloves of garlic, minced
- 1
shallot, finely chopped (to learn more about the benefits of shallot, click here25)
- 8
cups stinging nettle leaves and thin stems
- 1
tablespoon lemon juice
- 6
ounces feta cheese, crumbled
- 1
cup ricotta cheese
- Salt
and pepper to taste
Directions:
- Heat
oil in large skillet over medium heat. Add shallot and garlic and cook,
stirring often, until softened, approximately 1-3 minutes.
- Use
tongs to add nettle leaves to skillet in batches, adding more as each
addition cooks down and wilts. Add lemon juice, salt, and pepper and stir to
combine. The nettles are now safe to eat and handle.
- Transfer
the nettle mixture to a cutting board and chop finely with a sharp knife. In
a large bowl, combine the nettle mixture, cheeses, and more salt and pepper
as needed.
- Heat
oven to 350°F. While working with phyllo, prepare one sheet at a time and
keep the rest underneath a damp paper towel to stay cool and workable. Lay
one piece of phyllo pastry on a cutting board and brush with melted butter.
Lay a second piece of pastry on top, then cut the pastry sheet into thirds,
resulting in three long rectangles of pastry.
- Arrange
the first rectangle with the short end toward you, then place one tablespoon
of filling onto the end. Fold a corner up and to the left, covering the
filling and creating a small triangle. Continue triangle-folding the entire
length of the pastry.
- Brush
the outside of the completed triangle-shaped pocket with more melted butter
and set on a parchment paper-lined baking sheet. Continue creating pockets
until all the filling and pastry has been used.
- Bake
spanakopita for 15-20 minutes, or until golden brown and warmed through. Let
rest for five minutes before serving.
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Image credits (top to bottom): Stinging nettle leaves ©2018 Steven Foster
Stinging nettle patch ©2018 Steven Foster
Botanical illustration from 'Wildflowers of the British Isles' Vol. II by Harriet Isabelle Adams; 1910
Stinging nettle root ©2018 Steven Foster References
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