The ingredients in OXYBEET® were chosen for a reason. Here you can explore studies on beetroot, L-citrulline and vitamin C: what they found, the doses used and where to read the original studies.
All figures checked against the original sources. Reviewed in October 2026.
Nitric oxide (NO) is a gas your body produces naturally. Cells in the inner lining of your blood vessels release it, signalling the vessel walls to relax. The vessels widen, allowing blood to flow more freely.1
In a study of 238 healthy people, men's blood vessels maintained their ability to widen until around age 40, after which it declined each year. In women, it began to decline around age 50.2
Italian researchers showed that as we age, the availability of NO in blood vessels decreases and oxidative stress increases.3
Robert F. Furchgott, Louis J. Ignarro and Ferid Murad received the Nobel Prize for their discoveries about the role of nitric oxide (NO) as a signalling molecule in the cardiovascular system. Until then, no one knew that a gas could carry a signal from one cell to another.1
Nobel Prize in Physiology or Medicine
The scientists are not associated with OXYBEET®. The prize was awarded for the discovery of NO, not for any product. Photos: Jzubrovich (CC BY 3.0), Carlos Barretta (CC BY 2.0), Jeff Dahl (CC BY-SA 4.0), Wikimedia Commons.
Beetroot and L-citrulline each help your body make NO in their own way, and vitamin C helps NO form and protects it.
Beetroot contains natural nitrates. Bacteria on your tongue turn them into nitrites, which your body then uses to produce NO. That’s why it starts in the mouth.4
L-citrulline is well absorbed, and your body converts it into L-arginine. Cells in your blood vessels use L-arginine to produce NO. When you take L-arginine, your body breaks down much of it in the gut, so L-citrulline raises blood levels of L-arginine more effectively.11
In a cell study, vitamin C protected a substance from oxidation. Blood vessel cells need this substance to produce NO properly.19
Beetroot nitrates are among the most studied dietary components in vascular and sports research.
Healthy volunteers drank 500 ml of beetroot juice. After about three hours, their blood pressure fell by up to 10.4/8 mmHg. When they spat out their saliva, there was no effect, because bacteria on the tongue process the nitrates first.
Healthy adults · 500 ml of beetroot juice, taken once
Webb AJ et al. · Hypertension · 2008 [4] ↗68 people with high blood pressure drank 250 ml of beetroot juice every day for four weeks. The control group drank the same juice, but without nitrates. In the nitrate group, blood pressure fell by 7.7/2.4 mmHg, the ability of blood vessels to widen improved by about 20%, and arteries became more flexible. There were no changes in the placebo group.
68 participants, aged 18 to 85 · double-blind, placebo-controlled · 4 weeks
Kapil V et al. · Hypertension · 2015 [5] ↗Researchers reviewed 16 randomised trials involving 254 participants. Nitrates and beetroot juice reduced systolic blood pressure by an average of 4.4 mmHg. The higher the nitrate dose, the greater the effect.
Systematic review and meta-analysis · 254 participants
Siervo M et al. · J Nutr · 2013 [6] ↗Twelve healthy people aged 60 to 70 drank concentrated beetroot juice for three days. After drinking beetroot juice, their systolic blood pressure was 115 mmHg, compared with 120 mmHg when taking a placebo. Their bodies adapted more quickly to the effort when they started walking.
12 participants, aged 60 to 70 · double-blind, placebo-controlled · 3 days
Kelly J et al. · Am J Physiol · 2013 [7] ↗Eight men drank 500 ml of beetroot juice a day for six days. They needed 19% less oxygen during moderate exercise. During intense exercise, they lasted 675 seconds, compared with 583 seconds when taking a placebo.
8 men, aged 19 to 38 · double-blind, placebo-controlled · 6 days
Bailey SJ et al. · J Appl Physiol · 2009 [8] ↗In Denmark, 53.150 people were followed for 23 years. Those who consumed around 60 mg of nitrates a day from vegetables had a 15% lower risk of cardiovascular disease than those who consumed the least. That's roughly the amount of nitrates in a cup of leafy greens.
53.150 participants · observed over 23 years
Bondonno CP et al. · Eur J Epidemiol · 2021 [9] ↗An International Olympic Committee expert statement notes that there is good evidence for only a few food supplements: caffeine, creatine, buffering agents and nitrates.
IOC consensus statement · 2018
Maughan RJ et al. · Br J Sports Med · 2018 [10] ↗L-citrulline is an amino acid named after Citrullus, the Latin name for watermelon. Studies have found that it increases L-arginine levels in the blood. The body uses L-arginine to produce NO.
20 healthy volunteers took L-citrulline, L-arginine or a placebo for one week. L-citrulline increased blood levels of L-arginine more effectively than L-arginine itself. At the highest dose (3 g twice daily), the L-arginine to ADMA ratio increased from 186 to 278. ADMA is a substance that slows NO production. Urine tests showed more signs of NO production.
20 participants · double-blind, placebo-controlled · 1 week
Schwedhelm E et al. · Br J Clin Pharmacol · 2008 [11] ↗10 healthy men took 6 g of L-citrulline a day for seven days. During strenuous exercise, they lasted 661 seconds, compared with 589 seconds when taking a placebo. Mean arterial pressure was lower. The same dose of L-arginine had no effect.
10 men · placebo-controlled · 7 days
Bailey SJ et al. · J Appl Physiol · 2015 [12] ↗Eight healthy men received a single dose of 2, 5, 10 or 15 g of L-citrulline. There were no side effects at any of these doses, and blood L-arginine levels increased with the dose. The authors concluded that short-term use is safe and well tolerated.
8 men · 4 single doses
Moinard C et al. · Br J Nutr · 2008 [13] ↗A review of 13 randomised studies involving 206 participants concluded that citrulline taken before exercise reduced perceived exertion and muscle soreness 24 hours after exercise.
Systematic review and meta-analysis · 206 participants
Rhim HC et al. · J Sport Health Sci · 2020 [14] ↗41 men received 8 g of citrulline malate (L-citrulline combined with malic acid) or a placebo before exercise. When taking citrulline, they did 52.9% more repetitions in the final set, and muscle soreness was 40% lower at 24 and 48 hours after exercise.
41 men · double-blind, placebo-controlled · 1 workout
Pérez-Guisado J, Jakeman PM · J Strength Cond Res · 2010 [15] ↗For one month, 24 healthy people aged 60 to 70 drank either a placebo or a drink containing 520 mg of nitrates and 6 g of L-citrulline every day. Half the participants were women. Mean arterial pressure fell by 3.3 mmHg. During light exercise, heart rate and oxygen consumption were lower, and peak power on an exercise bike increased by 5.2%.
24 participants · double-blind, placebo-controlled · 1 month
Le Roux-Mallouf T et al. · Aging · 2019 [16] ↗One scoop of OXYBEET® contains 500 mg of vitamin C. That is 625% of the nutrient reference value.20
A review of 44 randomised studies found that vitamin C improved the function of the inner lining of blood vessels, known as the endothelium. The effect was greater in people at higher risk of cardiovascular disease and increased with the dose.
Systematic review and meta-analysis · 44 studies
Ashor AW et al. · Atherosclerosis · 2014 [17] ↗In people with high blood pressure, vitamin C administered directly into an artery improved blood vessels' ability to widen. When researchers blocked NO production, the effect disappeared.
49 participants · vitamin C administered into an artery
Taddei S et al. · Circulation · 1998 [18] ↗In blood vessel cells, vitamin C increased levels of tetrahydrobiopterin to as much as three times their original level. Without this substance, the enzyme that produces NO cannot work properly.
Laboratory study in cells
Heller R et al. · J Biol Chem · 2001 [19] ↗| Ingredient | In studies | In one scoop of OXYBEET® |
|---|---|---|
| L-citrulline | 6 g a day for 1 to 4 weeks.11,12,16 No side effects were reported after a single dose of 2 to 15 g.13 | 4500 mg |
| Beetroot | 70 to 500 ml of beetroot juice a day, approximately 350 to 600 mg of nitrates.7,8,16 | 4780 mg of beetroot juice concentrate powder |
| Vitamin C | The EU nutrient reference value is 80 mg a day.20 | 500 mg625% of the reference value |
You can find each study on PubMed or the publisher's website.
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