Vegetable Nitrates to Help Fight Respiratory Tract Infections

Nitric oxide (not to be confused with nitrous oxide, laughing gas) is a gaseous compound best known as the “open sesame” molecule released by our artery lining to enable our blood vessels to dilate. But it also has broad spectrum antifungal, antiviral, and antibacterial properties. It’s secreted into our airways as a first line of defense against respiratory infection, shooting up by more than 500 percent over baseline.

If you infect people with rhinovirus (the most common cause of the common cold), you can correlate the levels the exhaled nitric oxide the body is able to generate with the speed of symptom resolution. How can we boost levels even higher? By eating nitrate-rich vegetables.

To improve performance, some athletes dope with beet juice, which can also lower blood pressures in people with hypertension. The nitrate in beets and green leafy vegetables can be converted by the body into nitric oxide. So, can they be used to help clear infections? Perhaps it’s no coincidence that an infusion of spinach leaves has evidently been used since ancient times to treat respiratory symptoms. Within 45 minutes of drinking a double shot of beet juice, nitric oxide levels in our breath go up by 80 percent and stay elevated for at least three hours. So, researchers decided to test whether it could actually prevent infections.

Psychological stress, such as struggling through final exam week, appears to lower exhaled nitric oxide, but starting out with higher levels was associated with a lower likelihood of developing acute respiratory tract infection symptoms 5 to 10 days later. The question is, if you give students more vegetables, could they stave off infection? College students were randomized to “seven daily doses of beetroot juice” during their final exams. I wondered if they meant seven doses per day, but no, they just got one 70 ml shot every morning for a week, which is about a third of a cup (~80 ml) a day. In the beet group, exhaled nitric oxide went up and cold symptoms went down. Unfortunately, the control group didn’t drink anything special; so, one can’t discount the placebo effect. It would be interesting to see a double-blinded trial that used as its placebo a beet juice from which nitrate has been removed to nail down cause-and-effect, but, until then, it can’t hurt to eat more salads. Nearly all of the top twenty most concentrated nitrate sources are leafy greens, topped by arugula, which has about three times as much as beets (by weight) and more than twice as much as spinach.

This whole beetroot rabbit hole led me to a paper published in the American Journal of Respiratory and Critical Care Medicine entitled “Humming Greatly Increases Nasal Nitric Oxide.” A pair of Swedish researchers discovered that humming immediately caused a whopping 15-fold increase in exhaled nitric oxide. They suggested that perhaps “daily periods of humming can reduce the risk for sinusitis.” They even did a follow-up study to find the optimal humming frequency—130 hertz beat out 150 or 450.

So, they gave it a shot: A 64-year-old man suffering from severe rhinosinusitis constantly hacking up post-nasal drainage with severe headache and pressure around the clock leading to a month of severe sleep loss. His doctors tried steroid shots, antibiotics, guaifenesin, aspirin, zinc acetate, intranasal antihistamines, and oral decongestants, all to no avail. So, they told the guy to hum for an hour (but not so strongly or frequently to cause dizziness). The next day, he awoke with a clear nose, breathing easily for the first time in more than a month. The researchers mused that when yogis are clearing their heads chanting “Ommmm,” perhaps that humming is literally clearing their heads!