Maize (Zea mays L.): A Comprehensive Reference
1. Identity and Botanical Description
Taxonomic Classification and Nomenclature
Zea mays L. (maize) is not only one of the world's most extensively cultivated cereal crops but also a reservoir of pharmacologically active compounds with significant therapeutic potential. The plant belongs to the family Poaceae (Gramineae), the grass family, and is formally designated Zea mays Linnaeus. Common names vary by region and include maize (the internationally preferred scientific and agricultural term), corn (predominant in North America and Australia), Indian corn, and mealie (parts of sub-Saharan Africa). The medicinal preparation derived from the thread-like styles on the female flowers is known as corn silk or Stigma maydis.
Maize (Zea mays L.) with a high grain yield and dry matter production per unit area is a C4 plant and has an important place among the grains that are widely grown and cultivated throughout the world. Therefore, it is considered the "queen of cereals."
Botanical Origin and Domestication
Corn (Zea mays) evolved from wild Balsas teosinte (Zea mays subsp. parviglumis) in modern-day lowland Mexico, where it was brought under cultivation and domesticated beginning around 9,000 years ago. Archaeological remains provide evidence that corn agriculture was brought to the southwestern United States and the Colorado Plateau about 4,000 years ago, and spread to dominate food production systems throughout much of the Americas by the beginning of European colonization in the 15th century.
Anatomical Parts Used
This includes the diverse phytochemical constituents of maize — including polyphenols, phenolic acids (notably ferulic and p-coumaric acid), flavonoids, carotenoids, sterols, and tannins — distributed across its anatomical parts. The primary plant parts used in food, nutrition, and medicine include:
- Kernel (grain): The edible seed, consumed whole, milled into flour (masa, cornmeal), or processed into starch, oil, and fermented products.
- Corn silk (Stigma maydis): Corn silk (Zea mays L.) is the stigma of an annual gramineous plant named corn, which is distributed in many regions worldwide and has a long history of medicinal use.
- Corn stover, cob, bracts: Corn bracts can reduce blood lipid levels; corn silk reduces blood lipids and blood pressure; corn stover has hypoglycemic and antioxidant properties; corn cob can reduce blood sugar and regulate cholesterol levels.
Common Commercial and Supplement Forms
- Whole grain (dried or fresh kernels), cornmeal, masa flour (nixtamalized), corn starch, corn oil
- Corn silk: aqueous decoction (tea), ethanolic extract, encapsulated dry extract, standardized herbal supplement
- Isolated fractions: ferulic acid, lutein/zeaxanthin, resistant starch, soluble corn fiber, corn bran
2. Traditional and Historical Use
Mesoamerican and Indigenous American Traditions
For Native Peoples in Mesoamerica, corn was considered a sacred grain, a gift from the gods, and a source of life. Maize was more than just a staple food but helped inform a rich spiritual and cultural identity that lives on to this day. For generations, Indigenous communities evolved together with corn, hand-selecting for more suitable and adapted traits for human use and consumption, which concurrently shaped their oral histories, spiritual practices, and social structures.
For centuries, some Indigenous Peoples of the Americas planted corn, beans and squash or pumpkins together in mounds, in an intercropping complex known as the Three Sisters. Agriculturally, nutritionally and culturally, these three crops are complementary.
Of the many processing techniques developed by indigenous groups, nixtamalization is of particular importance. Nixtamalization of maize is a chemical process where kernels are cooked in alkaline solutions of lime or wood ash to allow for nutrients in maize to be more easily accessible. By the time of European colonization, Indigenous groups throughout the Americas had bred and adapted maize to a wide variety of environments and a vast number of cultural and culinary uses.
Some varieties of maize were traditionally grown in North America, like Hopi Blue Corn from the Southwest, Cherokee White Eagle from the Southeast, and Seneca Red Stalker from the Northeast.
For many cultures in the Americas, maize fulfills not just nutritional requirements, but also important religious, spiritual, and ceremonial roles.
Fermented and Ritualistic Preparations
One traditional use for maize is to make chicha, an alcoholic beverage made from fermented maize kernels. Chicha played a role in Incan ritual sacrifice, called Capacocha. Chicha is still prepared and consumed in the Andes today.
Traditional Medicinal Use of Corn Silk
Corn silk (Stigma maydis) — the thread-like styles found on the ears of Zea mays L. — has been widely used in traditional medicine by cultures across the world, including Native American, Chinese, Turkish, and European communities. Traditionally, corn silk tea has been valued for its diuretic and healing properties and used to manage various ailments such as urinary tract infections, kidney stones, diabetes, hypertension, and inflammation.
Corn silk is composed of the style and stigma of Zea mays L. Its medical value was first reported in "Southern Yunnan Materia Medica" in the Ming Dynasty. It was considered to be a heat-clearing and diuretic drug. In "Zhejiang Folk Herbal Medicine," the following has been reported: "Corn silk needs one liang. Decoction in water can cure diabetes." Recent studies have shown that corn silk can lower blood sugar levels.
It is used for the treatment of cystitis, edema, kidney stones, as a diuretic, for prostate disorder, urinary infections, bedwetting, and obesity. It soothes and relaxes the lining of the bladder and urinary tubules, hence reducing irritation and increasing urine secretion. It is also used as traditional medicine in many parts of the world such as Turkey, United States, and France.
3. Key Constituents and Active Compounds
Macronutrient Composition of the Grain
Maize (Zea mays L.), a key crop in the world's agriculture and nutrition, is desired for its high content of macronutrients such as carbohydrates, proteins, and lipids. Some varieties are very rich in protein (up to 14.34 g/100 g), while the highest fat content observed was 7.22 g/100 g; the highest carbohydrate contents ranged from approximately 79–80.64 g/100 g depending on variety. Glutamic acid is the predominant amino acid, while the least abundant is methionine.
Biofortified varieties, including Quality Protein Maize (QPM), provide enhanced levels of lysine, tryptophan, and provitamin A. Maize also supplies essential B vitamins and minerals such as iron, zinc, and magnesium; however, their bioavailability is reduced by antinutrients like phytates.
Sweet and flour maize were comparatively the best sources of micronutrients. Sweet maize yielded the highest values of potassium, thiamin, and magnesium, and flour kernels had the highest riboflavin and niacin content.
Phytochemical Constituents of the Grain
Maize is rich in phytochemicals, including ferulic acid, flavonoids, and carotenoids, which exhibit antioxidant and therapeutic properties.
The phytochemical constituents of maize include polyphenols, phenolic acids (notably ferulic and p-coumaric acid), flavonoids, carotenoids, sterols, and tannins distributed across its anatomical parts. Ferulic acid, a key secondary metabolite biosynthesized via the phenylpropanoid pathway, exhibits broad-spectrum bioactivity including antioxidant, anti-inflammatory, antidiabetic, and anticancer effects.
Beyond its nutritional value, Zea mays (corn) has a wide range of phytochemicals with proven anti-inflammatory properties, including flavonoids, anthocyanins, phenolic acids, and carotenoids.
Carotenoids present in maize grain include lutein and zeaxanthin, which are concentrated in the yellow endosperm. Marigold flowers, egg yolks, corn, and leafy green vegetables with dark green leaves like kale and spinach contain lutein. Zeaxanthin can be found in higher concentrations in foods that are yellow or orange, including egg yolks, corn, orange capsicums, tangerines, persimmons, mandarins, and oranges.
Phytochemical Constituents of Corn Silk
Phytochemistry studies have shown that the main bioactive components in corn silk include flavonoids, polyphenols, phenolic acids, fatty acids, and terpenoids. Pharmacological studies have shown that corn silk extract has various pharmacological effects, such as reducing blood lipids, lowering blood pressure, regulating blood sugar levels, anti-inflammatory effects, and anti-oxidation effects.
Corn silk extract contains a large amount of maysin, a type of flavonoid specific to corn. Maysin in corn silk extract is a flavone glycoside containing luteolin, a biologically active substance known to have high antioxidant and anticancer activities. Previous studies on maysin have evaluated its antiobesity, anti-cancer, anti-allergy, anti-oxidant, anti-asthma, and anti-dementia effects.
Mechanisms of Action
Antioxidant activity: The upper parts of corn silk were found to have the highest total antioxidant capacity (2.735 mg/g GA equivalents) and highest DPPH scavenging activity (IC₅₀ = 0.704 mg/mL). This is due to the accumulation of flavonoids and other phenolic compounds to protect maize DNA from the induction of ultraviolet damage.
ACE inhibition (antihypertensive): Proteomics and bioinformatics approaches were applied to identify corn silk bioactive peptides (CSBPs) that target angiotensin-converting enzyme (ACE) from the boiling water extract of corn silk (CSE). CSE significantly reduced systolic blood pressure levels in spontaneously hypertensive rats and inhibited ACE activity. A novel ACE inhibitory peptide, CSBp5, was identified; it significantly inhibited ACE activity and decreased systolic blood pressure in a dose-dependent manner. Docking analysis showed that CSBp5 occupied the substrate-binding channel of ACE and interacted with ACE via hydrogen bonds.
Anti-inflammatory activity (in vitro): In the course of screening marketed European anti-inflammatory herbal drugs for TNF antagonistic activity, a crude ethanolic extract of corn silk exhibited significant activity. The extract at concentrations of 9–250 µg/mL effectively inhibited the TNF- and LPS-induced adhesiveness of endothelial cells to monocytic cells. Similar concentration ranges of corn silk extract also blocked the TNF- and LPS-induced ICAM-1 expression on the endothelial cell surface.
Hypoglycemic mechanisms: Corn silk effectively improved blood glucose levels, regulated glucose and lipid metabolism by suppressing gene expression in the steroid biosynthesis pathway, and ameliorated hyperglycemia.
Lutein and zeaxanthin — macular protection: Lutein and zeaxanthin constitute the main macular pigments found in the yellow spot of the human retina, which protect the macula from damage by blue light, improve visual acuity, and scavenge harmful reactive oxygen species. They have also been linked with reducing the risk of age-related macular degeneration (AMD) and age-related cataracts. They may also enhance visual performance by decreasing chromatic aberration and enhancing contrast sensitivity.
4. Scientific Evidence by Area of Use
4.1 Ocular Health: Age-Related Macular Degeneration and Cataracts
Maize is one of the key dietary sources of lutein and zeaxanthin, which are the subjects of a substantial body of clinical research relevant to eye health.
Observational studies have reported that increased dietary intake and higher serum levels of lutein and zeaxanthin are associated with lower risk of age-related macular degeneration (AMD), especially late AMD. Randomized, placebo-controlled clinical trials have demonstrated that xanthophyll supplementation increases macular pigment levels, improves visual function, and decreases the risk of progression to late AMD, especially neovascular AMD. Current publications on the preventive and therapeutic effects of lutein and zeaxanthin on cataracts, diabetic retinopathy, and retinopathy of prematurity have reported encouraging results.
Lutein and zeaxanthin have potential health effects by preventing free radical formation, exhibiting protective properties against oxidative damage and reducing oxidative stress. These compounds have neuroprotective, cardioprotective properties, among others. These compounds have neuroprotective, cardioprotective, ophthalmological, antioxidant, anti-inflammatory, anti-cancer, anti-osteoporosis, anti-diabetic, anti-obesity, and antimicrobial effects.
Evidence strength: The link between lutein/zeaxanthin intake and AMD is supported by both epidemiological data and randomized controlled trials. However, the evidence relates to these isolated carotenoids as dietary supplements; trials using maize-derived lutein specifically as a food-based intervention are less common. The overall body of evidence is considered moderate-to-strong for supplement use in AMD but less definitive for food sources alone.
4.2 Blood Pressure (Hypertension)
Corn silk, a traditional Chinese medicine, has been found to exert an antihypertensive effect in clinical practice and trials. A systematic review and meta-analysis was conducted, with a systematic literature search through popular electronic databases up to October 2018. Randomized controlled trials (RCTs) comparing corn silk tea plus conventional antihypertensive drugs with conventional antihypertensive drugs alone were included, with the main outcome being total blood pressure-lowering efficacy. Five RCTs involving 567 participants were included.
These trials mainly studied the total blood pressure-lowering efficacy of corn silk tea plus conventional antihypertensive drugs compared with conventional antihypertensive drugs alone. The review could not provide valid evidence that corn silk tea improves edema, urine protein, and homocysteine, though a few trials revealed the beneficial role of corn silk tea combined with antihypertensive drugs on them clinically.
Although corn silk has been used as an aqueous decoction for anti-hypertensive healthcare in folk medicine, there are few reported studies on the certification of anti-hypertensive effects and mechanisms of corn silk in human subjects or animal models.
Evidence strength: Preliminary. The existing clinical evidence derives largely from small RCTs conducted in China using corn silk as an adjunct to pharmaceutical antihypertensives. Study quality is variable, and results cannot yet be generalized. More rigorous independent trials are needed before confident conclusions can be drawn about corn silk tea as a standalone antihypertensive intervention.
4.3 Blood Glucose Regulation and Diabetes
The female flower of Zea mays has an extended stigma that has historically been used to treat diabetes mellitus. Research has indicated that corn silk extracts enhance insulin sensitivity, decrease the level of fasting glucose, and decrease hyperglycemia in animal and human models.
Its bioactive substances, such as flavonoids and saponins, can stimulate the pancreatic activity and regulate the glucose metabolism, which makes it have a positive effect on the glycemic regulation and the prevention of the diabetes-related complications.
Corn silk (CS), an abundant, readily available, and affordable waste product of corn cultivation, has extensive therapeutic applications against various diseases including type 2 diabetes mellitus. Although the antidiabetic potential of CS is well-established in preclinical studies, the understanding of the mechanism of action behind its reported antidiabetic potentials is lacking.
With respect to whole-grain maize intake and glycemic outcomes, evidence is available from trials of whole grains as a category. Using random effects models, consuming 48–80 g whole grain per day (3–5 servings per day) was associated with approximately a 26% lower risk of type 2 diabetes compared with never or rare consumers of whole grains. However, this estimate applies to whole grains collectively and is not maize-specific.
Results from medium- and long-term trials showed no statistically significant difference in HOMA-IR, fasting plasma glucose, and insulin levels after whole grain compared to refined grain meals in healthy subjects.
Evidence strength: For corn silk specifically in diabetes, the evidence is predominantly preclinical (animal and in vitro) with limited human data of variable quality. For whole-grain consumption and T2D prevention, prospective cohort evidence is moderately strong, but direct causal evidence from maize-specific RCTs is limited.
4.4 Diuretic and Urinary Tract Effects
Corn silk is used for the treatment of cystitis, edema, kidney stones, as a diuretic, for prostate disorder, and urinary infections as well as bedwetting and obesity. It soothes and relaxes the lining of the bladder and urinary tubules, hence reducing irritation and increasing urine secretion.
However, direct human clinical evidence for the diuretic effect is conflicting. One study showed no significant difference in urine, sodium, and potassium excretion when corn silk (600 mL water extract) was tested on 38 volunteers for one week. Therefore, more clinical studies need to be carried out to substantiate the diuretic claim of corn silk, and there is a possibility that the dosage is too low to be effective.
Evidence strength: Weak for the diuretic claim in humans. The mechanistic rationale (high potassium content, flavonoid content) is established, but one of the few controlled human studies found no significant effect on urine output at the dose tested. The evidence is insufficient to support a definitive clinical claim.
4.5 Lipid Metabolism and Cardiovascular Health
Pharmacological studies have shown that corn silk extract has various pharmacological effects, such as reducing blood lipids, lowering blood pressure, regulating blood sugar levels, anti-inflammatory effects, and anti-oxidation effects.
At the level of whole-grain intake, epidemiological evidence supports an association with cardiovascular health. The cardiovascular benefits of fiber and, especially, cereal fiber, have been well documented: cereal fiber is strongly associated with a reduced risk of myocardial infarction, total and ischemic stroke, and incident cardiovascular disease. β-glucan from oats or barley, or a combination of whole oats and barley, and soluble fiber from psyllium reduce the risk of coronary heart disease; arabinoxylan and resistant starch may improve glycemic control. Note that this research applies to cereal fibers generally and is not exclusive to maize.
Evidence strength: For corn silk's lipid-lowering effects, the evidence remains largely preclinical. For cereal fiber and cardiovascular outcomes more broadly, the evidence is well established, but maize-specific fiber (as distinct from oat or barley fiber) has a considerably smaller dedicated evidence base.
4.6 Gut Health and Resistant Starch
Nixtamalization — cooking and steeping dried maize kernels in an alkaline solution made with water and lime or wood ash — provides several nutritional and sanitary benefits, including: increased niacin and iron bioavailability, increased calcium and resistant starch content, and decreased mycotoxin contamination.
Processing corn kernels with calcium hydroxide may increase resistant starch in products like corn tortillas and tamales. Resistant starch is a type of carbohydrate that resists digestion, instead fermenting and feeding healthy gut bacteria. Resistant starch may help manage blood sugar, promote gut health, and decrease cholesterol.
Whole grains are a good source of dietary fibres, vitamins, antioxidants, and phytochemicals, such as phenolic compounds (including ferulic acids and cinnamic), beta-glucan, and lignans, which have been reported to play a protective role in many metabolic diseases such as type 2 diabetes, obesity, and cardiovascular diseases.
Dietary fiber is associated with reduced risk of obesity, cardiovascular disease, type 2 diabetes, and colon cancer, yet nearly 95% of Americans fail to meet recommended intake levels. Dietary fiber also provides a primary substrate for microbes residing in the gastrointestinal tract, shaping ecological community diversity and metabolic capacity.
Evidence strength: Moderate for the prebiotic and gut health effects of cereal resistant starch from observational and mechanistic studies. Specific maize-derived resistant starch trials in humans are limited compared to those for oat fiber or other sources.
4.7 Niacin Bioavailability and Pellagra Prevention
Maize is typically rich in niacin, but most of it is not bioavailable for human use. Nixtamalization releases the previously bound niacin, making it easier for the body to absorb.
Maize-dependent diets that do not incorporate nixtamalization have historically contributed to outbreaks of pellagra and other nutrient deficiency-driven health problems.
The tryptophan in corn proteins is made more available for human absorption through nixtamalization, thus helping to prevent niacin deficiency (pellagra). Tryptophan is the metabolic precursor of endogenous niacin (Vitamin B3). Humans can convert tryptophan into niacin, thus helping to prevent pellagra.
Societies that have relied on corn as a staple but skipped nixtamalization have faced very high rates of pellagra (a niacin-deficiency disease), but this was never the case in Latin America, where nixtamalization was the norm.
Evidence strength: Strong and historically well-established. The relationship between non-nixtamalized maize diets and pellagra is one of the best-documented nutritional observations in the history of public health.
5. Body Systems and Health Areas
- Renal and urinary system: Traditional diuretic use of corn silk; preclinical evidence for reduction in urolithiasis; human evidence is limited and mixed.
- Cardiovascular system: Corn silk ACE inhibition and antihypertensive potential (mainly preclinical and small RCTs); whole-grain fiber intake linked to reduced CVD risk in prospective studies.
- Endocrine / metabolic system: Hypoglycemic effects of corn silk in preclinical models; whole-grain consumption inversely associated with T2D risk in cohort studies.
- Ocular system: Lutein and zeaxanthin from maize grain are closely associated with macular pigment density, AMD risk, and visual function through multiple RCTs and epidemiological studies.
- Gastrointestinal system: Dietary fiber, resistant starch, and prebiotic effects on gut microbiota; nixtamalized maize fiber as a source of short-chain fatty acid precursors.
- Antioxidant and anti-inflammatory: Ferulic acid, flavonoids, and anthocyanins provide broad-spectrum antioxidant and anti-inflammatory capacity demonstrated primarily in vitro.
- Neurological: 66 to 77% of the total carotenoid content in human brain tissue is made up of lutein and zeaxanthin. There is growing interest in the neuroprotective benefits of lutein and zeaxanthin, since they have been found in the hippocampus, cerebellum, frontal, occipital, and temporal cortices, and they also have potent antioxidant and anti-inflammatory capacities.
6. Dosage Forms and Reported Dosages
The following dosages are reported in the scientific literature and do not represent recommendations:
- Corn silk aqueous extract (diuretic study): 600 mL water extract tested on 38 volunteers for one week showed no significant difference in urine, sodium, and potassium excretion.
- Corn silk aqueous extract (antihypertensive, animal): Intravenous injection of 1.342 mg/kg boiling dialysate of corn silk decreased diastolic blood pressure by 63.8% ± 33.6% in normotensive anesthetized dogs. Oral administration of 260 mg/kg corn silk aqueous extract reduced intraocular pressure in eyes with ocular hypertension and lowered blood pressure in hypertensive subjects in one report.
- Corn silk powder (human diabetes study): Human male subjects were divided into groups receiving dosages of 1 g and 2 g of corn silk powder, respectively. The effect on blood sugar levels was checked every 7th day for 2 months, and HbA1c was measured before and after 60 days.
- Whole grain intake (epidemiological association): Consuming 48–80 g whole grain per day (3–5 servings per day) was associated with approximately a 26% lower risk of T2D.
- Nixtamalized maize (tortillas): The consumption of 150 g of tortilla (five tortillas) with 42% moisture provides about 350 kcal.
7. Safety Considerations and Interactions
General Safety of Corn Silk
Pharmacological studies (in vitro and in vivo) have shown corn silk's remarkable bioactivities as antioxidant, hyperglycemia reduction, anti-depressant, anti-fatigue, and effective diuretic agent. Some of the studies have confirmed the earlier findings and new research discoveries have proven that corn silk is safe and non-toxic. With the claims in healthcare potential, it is important to carry out clinical evaluations to substantiate the claims and further enhance the confidence in its beneficial therapeutic effects for human consumption.
When corn silk extract is consumed in excess, there are some side effects such as allergic reactions and stimulation of uterine contraction in rabbits due to unknown toxic substances.
Potential Interaction with Anticoagulants (Warfarin)
Corn silk contains large amounts of vitamin K. Vitamin K is used by the body to help blood clot. Warfarin (Coumadin) is used to slow blood clotting. By helping the blood clot, corn silk might decrease the effectiveness of warfarin (Coumadin).
Interaction with Diuretic Drugs
Corn silk seems to work like "water pills" (diuretics). Corn silk and "water pills" might cause the body to get rid of potassium along with water. The high potassium content observed in corn silk extract, and diuretic and uricosuric properties discovered in corn silk, suggest that the fall in blood pressure by corn silk may result from the diuretic activity or direct vasodilatation.
Mycotoxin Contamination — A Critical Safety Concern for Maize
Maize (Zea mays L.) stands as a vital staple food globally, holding significant nutritional and economic value. However, its susceptibility to mycotoxin contamination under stressful environmental conditions poses a considerable concern.
Maize is frequently contaminated with multiple mycotoxins, especially those produced by Aspergillus flavus and Fusarium verticillioides. As mycotoxin contamination is a critical factor that destabilizes global food safety, an updated overview of the co-occurrence of aflatoxin B1 (AFB1) and fumonisin B1 (FB1) in maize is essential.
Aflatoxins have the highest acute and chronic toxicity of all mycotoxins; hence, the maximal concentration in agricultural food and feed products and their commodities is regulated worldwide.
Nixtamalized corn has several benefits over unprocessed grain: it is more easily ground, its nutritional value is increased, flavor and aroma are improved, and mycotoxins are reduced by up to 97–100% (for aflatoxins).
Emerging evidence emphasizes the potential for herb–drug interactions, which may pose serious risks to patient health, particularly among elderly individuals and those with chronic diseases. In light of the increasing use of herbal remedies worldwide, potential interactions between conventional drugs and commonly used medicinal plants including maize-derived preparations warrant attention.
Potential Interaction with Antidiabetic Drugs
Given the documented hypoglycemic properties of corn silk in preclinical and limited human research, the potential for additive glucose-lowering effects when corn silk is used alongside insulin or oral hypoglycemics should be noted. This is a theoretical but mechanistically plausible interaction, particularly for preparations used at higher doses.
References
Go back