Newsletter #297

Over the past year, you might have seen some videos on Tik Tok talking about nose breathing, and supposed mind-blowing benefits that people have observed from taping their mouths shut at night.

A lot of this is probably overstated, obviously. But this fad may not be not wholly unfounded.

For one thing, it has been speculated for some time that breathing through your nose might lead to lower blood pressure. This may be mediated in large part through nitric oxide. Nitric oxide relaxes and widens the walls of your blood vessels. This, in turn, enhances blood flow and vascular function, and lowers blood pressure.

We've discussed, in previous newsletters, the key role of the oral microbiome in the nitric oxide pathway, and how certain antiseptic mouthwashes may promote higher blood pressure by demolishing bacteria in the mouth that help generate nitric oxide. But emerging evidence suggests that the nose may be just as critical in this respect. For one thing, the paranasal sinuses produce four times as much nitric oxide as the mouth. These empty spaces in the head have historically been perceived as a bit of an anatomical enigma, lacking an obvious physiological function, but it has recently been hypothesized that nitric oxide synthesis could be the primary function of the paranasal sinuses.

So, it’s biologically plausible that nasal breathing could improve endothelial function, and in turn lower cardiovascular risk. However, there hadn’t been any trials that directly tested this potential benefit of nose breathing in human trials…until very recently.

To examine how different routes of breathing might influence blood pressure, researchers at Florida State University recruited 20 healthy young adults and had them participate in a series of breathing experiments.

To begin, participants sat quietly at the lab and breathed freely for five minutes, in order to establish their preferred breathing rate. Then, in random order, they were asked to engage in five minutes of nasal breathing, with their mouth closed, as well as five minutes of exclusively mouth breathing (nose clipped).

When the researchers compared the data, they found that mean blood pressure and diastolic blood pressure were significantly lower when participants engaged in nasal breathing, compared to mouth breathing.

Notably, this was accompanied by improvements in heart rate variability (HRV).

Heart rate variability simply refers to the variation in the time interval between heartbeats, and it has emerged as a useful surrogate measure of the balance of the autonomic nervous system. One way that scientists can measure HRV is by looking at the wave structure of the heart rhythm, and the ratio of the various categories of waves. Certain frequency bands are associated with differences in autonomic activity.

In this study, the researchers found that nasal breathing led to an increase in the high-frequency contribution to HRV in these subjects, as well as a decrease in the ratio of low-frequency to high-frequency bands. Both are indicative of parasympathetic dominance.

Taken together, this suggests that nasal breathing was shifting the balance of the autonomic nervous system more toward parasympathetic activity, which is relevant because sympathetic dominance dramatically increases as we get older, and is thought to play a pivotal role in age-related hypertension.

To put the findings into perspective, the improvement in blood pressure at rest observed here was fairly small (~4 mm Hg). However, it's pretty impressive when you consider that this impact was elicited in healthy 18-year-old subjects with just five minutes of nose breathing. Furthermore, BP reductions at around that magnitude have been shown to result in significantly decreased risk of heart attack and stroke, even in people with normal blood pressure values.

In the future, it would be helpful to see the impact of nasal breathing on blood pressure and autonomic control in people with cardiovascular risk factors, as well as longer-term nasal breathing interventions.

👾  For decades, there have been reports of a pervasive low-frequency sound, known as “The Hum.”

The Hum has been reported around the world, but is only perceptible to a relatively small percentage of the population.

Now, whether this hum is actually a physical sound with a single unified cause is…debatable at best (although it sounds like a good premise for a sci-fi film). As the article suggests, it’s probably attributable to tinnitus or other auditory issues, or maybe local noise emitting mechanical devices.

Apparently, one example of The Hum was ultimately determined to be due to a mating call from a very loud fish.

Despite the name, the primary ingredient in Lemon Zinger is not citrus — it’s actually hibiscus leaves. And this is relevant for our discussion today because hibiscus has been shown to lower blood pressure, perhaps by increasing nitric oxide production.

In one trial, volunteers who drank hibiscus tea observed a 7.2 mm Hg decrease in their systolic blood pressure, with even more dramatic reductions in individuals who entered the study with hypertension. One thing that jumped out at me about this study: The researchers acquired the hibiscus flowers used for the tea from Celestial Seasonings, so ostensibly they are a pretty legit source.

This course takes a deep dive into the various classes of phytochemicals in plants, where they are found, their powerful health effects, and how intelligently-devised smoothies can help optimize our intake of these compounds.

For more practical information on using smoothies to enhance nutrition, please refer to our How-to Guide for smoothies.

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