Nitrates in Arugula: Should You Be Worried?

Naturally rich in nitrates, green leafy vegetables such as arugula and spinach are a major source of dietary nitrates. These controversial compounds can be converted into nitrites and further into harmful nitrosamines, but they may also provide a variety of health benefits. Read on to get the full scoop on arugula and nitrates.

Nitrate Content of Arugula

When it comes to foods that are rich in nitrates, arugula is right there on top of the list. On average, arugula contains even more nitrates than spinach and beetroot, both of which are frequently cited as examples of high-nitrate vegetables. According to a study published in Nutrition Research Reviews, the nitrate content of arugula has been found to range from 25 to 118 mmol/kg (5th and 95th percentile). For the sake of comparison, the nitrate content of spinach ranges from 1 to 40 mmol/kg. (1)

It is also worth noting that the nitrate content of arugula grown in winter is typically much higher than the nitrate content of arugula grown in summer, and that in general, organically grown leafy green vegetables contain lower levels of nitrates than their conventionally grown counterparts. What's more, baby arugula has been found to accumulate significantly less nitrates than more mature leaves. (2, 3) This is consistent with other studies that have found significantly lower levels of nitrates in microgreens and baby greens than their mature counterparts.

Arugula, Nitrates and Cancer

Despite being rich in nitrates, arugula as part of a balanced diet probably won't increase your risk of developing cancer (4). In fact, there is some evidence that green vegetables might do just the opposite, and actually provide protection against cancer. A systematic review of existing studies on nitrate/nitrite intake and gastric cancer concluded that a high intake of nitrates is associated with a weak but statistically significant reduced the risk of gastric cancer. A high intake of nitrites, by contrast, appeared to increase the risk of gastric cancer (5).

As you may know, many plant-based foods, especially green leafy vegetables like arugula, are rich in nitrates, while processed meat products are typically rich in nitrites. Right after harvest, plant foods like arugula generally contain little or no nitrite, but nitrates can be converted into nitrites later by certain microorganisms. (6, 7)

Now, despite the fact that nitrates can be converted into nitrites and further into carcinogenic nitrosamines in the human body, dark green leafy vegetables in general are not thought to cause cancer but rather to protect against it. Why? Because green leafy vegetables also contain a wide range of beneficial compounds (4).

For example, the vitamin C in green leafy vegetables like arugula may help inhibit the conversion of nitrites into nitrosamines (8), and phytochemicals found in green leafy vegetables may help fight cancer through multiple mechanisms. In particular, Brassica vegetables like arugula (and its more famous cousins, kale and broccoli) have been found to contain phytochemicals called glucosinolates. While glucosinolates themselves are relatively inert, they can be converted into isothiocyanates, such as erucin, which have been shown to inhibit the proliferation of cancerous cells and to promote their self-destruction in laboratory studies (9, 10).

However, the debate over the link between nitrates and cancer continues, and in some countries authorities have taken pre-cautionary measures to limit the nitrate levels in some vegetables. The European Union, for example, has set a maximum level for nitrate in arugula and a handful of other high-nitrate vegetables (11).

Cardiovascular Benefits

Interestingly, while some people may still worry about the nitrates in green leafy vegetables, there is evidence that nitrates from vegetables like arugula may actually offer some health benefits because they can act as precursors to nitric oxide (12). Nitric oxide is one of the most important molecules in the body and is involved in a wide range of physiological processes. One of its most important roles is its ability to make blood vessels bigger, and a growing body of evidence suggests that it may play a pivotal role in keeping the cardiovascular system healthy.

Indeed, a review published in 2013 concluded that overall, studies suggest that dietary nitrate acutely lowers blood pressure in healthy humans, but noted that more research was needed, especially in individuals with hypertension and at risk of CVD (1). Since the publication of this review, further studies have been conducted, and there is now more convincing evidence that dietary nitrate can also provide benefits for people with hypertension (13).

Other Potential Benefits

Research suggests that dietary nitrate can also increase the efficiency of the mitochondria that power our cells, which essentially means that the body can do more work with the same amount of oxygen (14). This is precisely the reason why so many runners and other athletes swear by beetroot juice as a natural performance enhancer (beetroot is packed with nitrates, though it does not contain quite as much nitrates as arugula).

Because of their ability to boost cellular efficiency, dietary nitrates from foods like arugula could also prove to be beneficial for people living at high altitudes, where oxygen is limited, and for people suffering from certain lung diseases and sleep disorders that are characterized by low oxygen. However, more research is still needed.

The Bottom Line

Not only do nitrates from whole food sources like arugula seem to be remarkably safe for healthy adults, they may also offer some cardiovascular benefits as well as other health benefits. However, some caution is in order. A report by The American Academy of Pediatrics points out that dietary nitrates can cause infant methemoglobinemia, colloquially known as 'blue baby syndrome', which is why it is recommended that foods with naturally occurring nitrates be avoided before three months of age (15).

Finally, don't forget that moderation is key. So, while you don't need to be too worried about the nitrates in arugula, you should also not overdo it.

References

1. D. Hobbs et al (2013). The effects of dietary nitrate on blood pressure and endothelial function: a review of human intervention studies. Nutrition Research Reviews, 26: 210-222.
2. A. Ferrante at al (2002). Preharvest and postharvest strategies for reducing nitrate content in rocket (Eruca sativa). ISHS Acta Horticulturae 628.
3. C. Colla et al (2018). Nitrate in fruits and vegetables. Scientia Horticulturae, 237, 221-238.
4. Marina Cavaiuolo and Antonio Ferrante (2014). Nitrates and Glucosinolates as Strong Determinants of the Nutritional Quality in Rocket Leafy Salads. Nutrients, 6(4): 1519-1538.
5. P. Song et al (2015). Dietary Nitrates, Nitrites, and Nitrosamines Intake and the Risk of Gastric Cancer: A Meta-Analysis. Nutrients, 7(12): 9872-9895.
6. J. Hsu et al (2009). Nitrate and nitrite quantification from cured meat and vegetables and their estimated dietary intake in Australians. Food Chemistry, 115 (1): 334-339.
7. A. Gorenjak (2013). Nitrate in vegetables and their impact on human health. A review. Acta Alimentaria, 42 (2)(2):158-172.
8. Q. Zhan et al (2012). Esophageal Carcinoma. Recent Advances in Cancer Research and Therapy, p. 493-534
9. X. Wu et al (2009). Are isothiocyanates potential anti-cancer drugs? Acta Pharmacol Sin., 30(5): 501-512.
10. O. Azarenko et al (2014). Erucin, the major isothiocyanate in arugula (Eruca sativa), inhibits proliferation of MCF7 tumor cells by suppressing microtubule dynamics. PLoS One, 9(6):e100599.
11. Commission Regulation (EU) No 1258/2011 of 2 December 2011 amending Regulation (EC) No 1881/2006 as regards maximum levels for nitrates in foodstuffs.
12. A. Torregrossa et al (2011). Nitric oxide and geriatrics: Implications in diagnostics and treatment of the elderly. Journal of Geriatric Cardiology, 8(4): 230-242.
13. C. Kerley et al (2018). Dietary nitrate lowers ambulatory blood pressure in treated, uncontrolled hypertension: a 7-d, double-blind, randomised, placebo-controlled, cross-over trial. The British Journal of Nutrition, 119(6), 658-663.
14. F. Larsen et al (2011). Dietary Inorganic Nitrate Improves Mitochondrial Efficiency in Humans. Cell Metabolism, 13(2), 149-159.
15. American Academy of Pediatrics (2005). Infant methemoglobinemia: the role of dietary nitrate in food and water. Pediatrics, 116(3):784-6.