Fennel Seeds Are a Potent Booster of Nitric Oxide

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Story at-a-glance -

  • Nitric oxide is vital to your health because it is produced by nearly every type of cell in your body and is necessary for healthy blood vessels; fennel seeds increase your body’s production of nitric oxide
  • Popular as a post-meal mouth freshener, fennel seeds have significant free radical scavenging potential and oxidative DNA damage preventive activity that may protect you from Alzheimer’s and Parkinson’s disease
  • Because they boost your vascular health, fennel seeds are a convenient, cheap and portable source of nitrates for nearly anyone, including athletes
  • If you are able to tolerate them, I highly recommend fennel seeds as an easy way to increase your nitric oxide levels; I love fennel seeds and eat them as part of my breakfast

By Dr. Mercola

If, like me, you’re a fan of fennel, you may already know about some of its health benefits. I love fennel because it’s easy to grow — I affectionately refer to the section of my property where it is established as the “fennel forest.” Beginning with a single plant, I have watched fennel steadily multiply across my yard as volunteers.

Because I have access to an abundant supply, I eat 1-2 tablespoons of fennel seeds soaked overnight daily. I soak them overnight for use in my breakfast the next morning. There are particular health benefits attributed to the seeds, which are actually a fruit, not a seed. That said, I’ll continue to refer to them as seeds in this article since that is how they are commonly known.

If you have not yet tried fennel seeds, you may be interested to know they are an excellent, cheap and convenient source of healthy nitrates. Fennel seeds are able to increase nitric oxide in your body, which has several distinct health benefits.

What Is Nitric Oxide and Why Is It Important to Your Health?

Nitric oxide is vital to your health because it is produced by nearly every type of cell in your body. It is one of the most important molecules needed for healthy blood vessels. While you often hear about the negative effects of free radicals, your body actually needs some to be healthy.

Nitric oxide is a free radical that acts as a vasodilator, which means it causes your blood vessels to expand and dilate, promoting blood flow and lowering your blood pressure. It also improves your immune function, stimulates the thinning of your blood and decreases blood viscosity, which in turn decreases platelet aggregation.

As such, nitric oxide helps reduce your risk of developing a life-threatening blood clot. Another benefit of nitric oxide is that it's a powerful anabolic stimulus known to help increase your lean body mass. When you increase your muscle mass, your body is more easily able to burn fat for fuel.

Burning fat for fuel remains a concept that escapes many people. It is a state of health so radically life-changing that you really must try it to fully appreciate its benefits.

Anyway, the increased presence of free radicals such as nitric oxide signals your body to create more mitochondria — a process called mitochondrial biogenesis, which is necessary to keep up with the heightened energy requirement.

Your mitochondria are the energy storehouses of your cells and are also the energy source for your skeletal muscles. Mitochondrial changes can have a positive impact on your skeletal muscle, fat tissue and even your liver, brain and kidneys.

A 2013 study published in the British Journal of Clinical Pharmacology1 underscores the positive vascular effects of dietary nitrates via the nitrate-nitrite-nitric oxide pathway. The study authors stated:2

“Dietary nitrate has been demonstrated to have a range of beneficial vascular effects, including reducing blood pressure, inhibiting platelet aggregation, preserving or improving endothelial dysfunction [and] enhancing exercise performance in healthy individuals and patients with peripheral arterial disease.

Preclinical studies with nitrates or nitrites also show the potential to protect against ischemia-reperfusion injury and reduce arterial stiffness, inflammation and intimal thickness.”

Are You Familiar With Fennel?

Fennel (Foeniculum vulgare) is a perennial belonging to the carrot family — home to several aromatic plants with hollow stems, including celery, cilantro, dill and parsley.

About fennel, National Geographic says, “Unlike its graceful relatives, however, fennel is clunky and funny-looking. It has a bulbous, crunchy, white stem topped with green stems and feathery leaves. Like anything with a fat bottom and a scrawny top, it inevitably invites jokes.”3

Fennel has a mild but distinctive licorice flavor that is sometimes confused with anise. While anise has a pungent taste reminiscent of black licorice, fennel, which some refer to as "sweet anise," has a sweeter, more delicate flavor.4 Unlike other vegetables and herbs, almost every part of the fennel plant including the base, stalks, leaves and seeds is edible.

Fennel is well-regarded as an essential oil. The characteristic anise-like odor of fennel, which results from its essential oil, gives it wide appeal as a flavoring agent in alcoholic beverages, baked goods, fish and meat dishes and even ice cream.5

Even though it is classified as an herb, many chefs use the lower part of the fennel plant, or the bulb, as a vegetable, adding it to salads, soups and stews.

The fronds that grow on the top of the plant may be used in salads or as a garnish, much like dill. You’ll get the most benefit if you grow your own fennel plants. Personally, I have not had much success in growing fennel as a bulb. My fennel bulbs are typically small and thin. For that reason, I mainly appreciate fennel for its seeds.

As mentioned, I have a veritable forest of fennel in my yard. I planted it once and since it is self-propagating, it continues to multiply. Because it is so productive, you may see fennel growing wild along roadsides, in nature preserves and open pastures. Fennel seeds are often used as post-meal mouth fresheners across the Indian subcontinent and elsewhere.

For maximum freshness, fennel seeds are harvested just as the flowers are beginning to dry out and turn brown. I simply clip the tops of the stalks containing flower heads and store them in a dark place for a week or two until they are fully dried. At this point, the seeds easily fall out of the flower heads and can be separated from the dried plant debris.

The Many Health Benefits of Fennel

The use of fennel dates back to ancient Rome, where it was used as a contraceptive. In addition, Pliny the Elder was said to have recommended fennel for epilepsy, gout, mange, scorpion stings and snakebite.6 According to the California College of Ayurveda, fennel is one of the best digestive herbs.7

They suggest adding it to your cooking, ingesting it in capsule form or drinking fennel tea. Furthermore, they note, “Some of the other marvelous features of fennel include: It dispels gas, it’s a diuretic, great for children’s colic, calming to the nerves, clears phlegm, increases the flow of milk in lactating mothers and aids in menstruation.”8

Authors of a 2014 study9 published in the journal BioMed Research International assert fennel has been used in traditional medicine to treat digestive, endocrine, reproductive and respiratory ailments, as well as a galactagogue agent for breastfeeding mothers. The researchers stated:10

“Findings based on its traditional uses and scientific evaluation indicate [fennel] remains the most widely used herbal plant. It has been used for more than 40 types of disorders. Phytochemical studies have shown the presence of numerous valuable compounds, such as volatile compounds, flavonoids, phenolic compounds, fatty acids and amino acids.

Compiled data indicate [fennel’s] efficacy … as antimicrobial, antiviral, anti-inflammatory, antimutagenic, antinociceptive, antipyretic, antispasmodic, antithrombotic, apoptotic, cardiovascular, chemomodulatory, antitumor, hepatoprotective, hypoglycemic, hypolipidemic and memory-enhancing.”

The polyphenols found in fennel include coumarins, flavonoids, furanocoumarins, phenolic acids and tannins, as well as common constituents like caffeic acid, chlorogenic acid, cinnamic acid, ferulic acid, quercetin and rutin.11 Upon analyzing 23 fennel samples, the study authors concluded:12

  • Apigenin and quercetin were the most abundant flavonoids
  • Phenolic compounds promote increased antibacterial activity
  • Samples with higher antioxidant activity revealed higher antiglycative activity (glycation relates to damage from high blood sugar)
  • Seed extracts showed moderate to good inhibitory activities against three foodborne pathogens

Prevent Free Radical Damage With Fennel Seeds

In addition, fennel has been shown to have significant free radical scavenging potential and oxidative DNA damage preventive activity.13,14 One study, published in the journal BioMed Research International,15 screened the free radical scavenging activity of fennel seeds and carom seeds (another aromatic seed used in India, most especially in the state of Gujarat16).

Notably, both seed extracts were shown to mitigate oxidative damage in calf thymus DNA. The study authors said, “These plant extracts can be considered as significant source of natural antioxidants that can withstand the deleterious effects of many diseases such as cancer, atherosclerosis, diabetes, inflammation and aging.”17

Fennel Seeds Promote Vascular Health

A 2012 study from India18 suggests fennel seeds promote healthy vascular function mainly due to their high level of nitrites and nitrates. The researchers noted:

“Results from our study show that fennel seeds contain significantly higher amount of nitrites when compared to other commonly used post-meal seeds.

Furthermore, our study confirmed the functional effects of fennel derived-nitrites … that describe the promotion of angiogenesis (the formation of new blood vessels from pre‐existing ones), cell migration and vasorelaxation (dilation of blood vessels).

We also showed that chewing fennel seeds enhanced nitrite content of saliva. Thus, our study indicates the potential role of fennel derived-nitrites on the vascular system.”

Boost Your Athletic Performance With Fennel Seeds

If you are an athlete looking to boost your performance and would like a convenient alternative to consuming nitrate-rich vegetables like beetroot, celery, spinach and Swiss chard, consider fennel. By eating fennel seeds, you can get a significant bump in nitric oxide production, which will, in turn, open up your blood vessels and positively impact your workout.

Given their availability, affordability (especially if you grow your own fennel) and portability, fennel seeds are a lightweight, nonperishable source of nitrates that is ideal for gym rats, outdoorsmen and high-performance athletes.

As mentioned in the featured video, it’s possible chewing fennel seeds may help mountain climbers maintain oxygen levels at high altitudes and aid in preventing high altitude pulmonary edema (HAPE) — the most common cause of death resulting from exposure to high altitude.19

Fennel Shown Effective as a Treatment for Sun Damage

In a 2016 study,20 Korean researchers sought to determine if fennel could be useful to alleviate ultraviolet B (UVB)-induced photoaging. The study authors suggested fennel offers photoprotective benefits for preventing and treating sun damage to your skin, further stating:21

“Fennel significantly increased the production of collagen, elastin and transforming growth factor-beta 1 (TGF-beta 1) levels, while blocking matrix metalloproteinases (MMPs) production in UVB irradiation-induced hairless mice, which were consistent with the result in normal human dermal fibroblasts (NHDFs).

Furthermore, fennel dose-dependently decreased the production of reactive oxygen species (ROS) and lactate dehydrogenase (LDH) by promoting the nuclear amount of Nrf2 and enhancing the expression of cytoprotective antioxidants such as glutathione (GSH).

Fennel also significantly quenched UVB-induced phosphorylation of extracellular signal-regulated kinase (ERK) and p38 in NHDFs. Based on our present results, we suggest the potential of [fennel] for the prevention of skin damage caused by solar radiation.”

Fennel Shown to Counteract Lead Toxicity; Minimizes Neuronal Toxicity Associated With Alzheimer’s and Parkinson’s

Fennel also appears to be useful for ameliorating the effects of lead toxicity. While lead exposure has been greatly reduced in recent decades, it continues to be an issue in certain areas, especially impoverished urban areas.

A 2018 study published in the journal Drug and Chemical Toxicology22 evaluated the neuroprotective effects of fennel seed extract on lead-induced neurotoxicity in the brains of lab mice.

Nine groups of mice were administered with 0.1 percent lead and 75 percent and 100 percent ethanol extracts of fennel seeds at doses of 200 milligrams (mg) per kilogram(kg) per day and 20 mg/kg/day. The researchers noted the maximum antioxidant effect was found in the 75 percent ethanol extract.

Based on their measurement of the gene expression levels of oxidative stress markers, including superoxide dismutase 1 (SOD1) and peroxiredoxin 6 (Prdx6), as well as the three isoforms of amyloid precursor protein (APP), including APP common, 770 and 695, in the cortex and hippocampus of the various mice groups, they commented:23

“[A] significant increase in APP 770 expression level [was observed] while a substantial decrease was observed for SOD1, Prdx6 and APP 695 expression in the lead-treated groups.

Interestingly, the deranged expression levels were significantly normalized by the treatment with ethanol extracts of fennel seeds (specifically at dose of 200 mg/kg/day). Furthermore, the lead-induced morphological deterioration of cortical neurons was significantly improved by the ethanol extracts of fennel seeds.

In conclusion, the present findings highlight the promising therapeutic potential of fennel seeds to minimize neuronal toxicity by normalizing the expression levels of APP isoforms and oxidative stress markers.”

By way of explanation, lead exposure normally reduces brain cortical and hippocampal expression levels of SOD, whereas in this study scientists demonstrated fennel seeds restored protective levels of SOD in the lab mice exposed to lead.

Research has linked mutations in the SOD gene to familial amyotrophic lateral sclerosis (ALS)24 and also asserts it as a major target of oxidative damage in brains affected by Alzheimer’s and Parkinson’s disease.25 Due to their potential to restore SOD levels, it’s possible fennel seeds could be helpful in preventing these diseases.

When to Avoid Fennel

In most cases, you should be able to tolerate fennel seeds when eating them in moderation. If you have a sensitivity to other members of the carrot family, you should avoid fennel seeds and other fennel preparations.

At least one study associated the drinking of fennel tea with early onset puberty in girls.26 For this and other reasons, fennel is not recommended for children under age 18 unless approved by a doctor.

On a positive note, fennel has been shown to possess antihirsutism activity, helping to combat excessive facial hair growth in a study involving 38 women who successfully applied a 1 percent fennel cream.27

In closing, if you are able to tolerate them, I highly recommend fennel seeds as an easy way to increase your nitric oxide levels and boost your vascular health.