New research this week
This week: what a smart ring can and cannot tell about anxiety, how accurate the heart rate variability on your wrist is, a light-guided breathing session tested against a dark room, how intense fast breathwork really is, and twelve trials of magnesium for sleep.
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Stimulation and devices
People with more anxiety slept a little differently on a smart ring, by margins far too small to tell one person from another
Smart rings turn your overnight pulse and movement into sleep stages and a heart rate variability score, and there is growing interest in whether those numbers could flag anxiety or depression. Researchers in Finland asked 1,290 people in their mid-thirties, drawn from a study that has followed everyone born in one region in 1986, to wear an Oura Ring for two weeks and fill in standard anxiety and depression questionnaires. On average, people with moderate to severe anxiety got about 11 minutes less deep sleep a night, 9 minutes less dream sleep and a heart rate two beats higher, though the heart rate gap disappeared at weekends. Each difference accounted for less than one percent of how much people varied.
What it means. A night of less deep sleep on your ring is not a sign that you are anxious. These differences are real across a crowd of a thousand people and far too small to read off one person's numbers. And because everything was measured at once, nobody can say which way it runs, whether anxiety disturbs sleep or poor sleep feeds anxiety.
Worth knowing. The summary at the top of the paper says the group with depression and anxiety also had lower heart rate variability. The paper's own table shows that difference was not statistically reliable, on weekdays or at weekends.
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Measurement
The heart rate variability on a watch or ring comes close to a medical recording when you sit still, and this review could not say how it does the rest of the time
Watches and rings read your pulse by shining light into the skin and measuring what comes back, rather than picking up the heart's electrical signal the way a hospital recording with chest electrodes does. Researchers gathered 43 studies that compared the two in healthy people, and ten reported enough to be combined. At rest, the wearable readings landed close to the chest recording on average, off by about a fifth of the usual difference between one person and the next, and one of the two common measures tended to read slightly high.
What it means. The number on your wrist is measuring something real, not inventing it. But the reviewers say plainly that their result does not carry over to sleep, exercise, stress or ordinary daily life, which are the conditions most people wear a device in. Most of the studies also left out the figures needed to say how far off a single reading can be.
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Breathing
Fifteen minutes of light-guided slow breathing left people less stressed than lying in the dark, without moving the heart measure it is meant to work on
Coherent breathing means breathing slowly, five or six breaths a minute, and it is usually promoted on the grounds that it raises heart rate variability, a sign that the body's calming branch is active. Twenty-nine young adults in France were put through a standard stress test (cold water, mental arithmetic, being judged), then spent fifteen minutes either breathing in time with pulses of blue light and sound from a commercial device or lying in a dark room; three weeks later they did the other. Stress was rated about 30 percent higher after the dark room, and after the device people felt less sleepy and in a better mood. Their heart rate variability and brain recordings did not differ.
What it means. Paced slow breathing after something stressful left people feeling better than plain rest did, at least in the minutes afterwards. The reason usually given, that it shifts your heart rhythm, is not what showed up here. And with light, sound and breathing delivered together, the study cannot say whether the device added anything to the breathing.
Worth knowing. The company that makes the device employed four of the authors, ran the study in its own lab and recruited partly from its own staff. People also always knew which session they were in, so the comparison is with a dark room, not with a convincing fake.
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Breathing
Half an hour of fast breathing produced altered states in the range reported for moderate psychedelic doses, in 48 therapists who tried it
Fast, deep, connected breathing, taught under names like conscious connected breathing or holotropic breathwork, lowers the carbon dioxide in your blood and commonly brings tingling, light-headedness and cramping. Researchers in Berlin put 48 psychiatrists and psychotherapists through a four-hour workshop built around thirty minutes of it, then asked what they had felt and who they thought it could help or harm. Their scores on a standard altered-states questionnaire fell in the range other studies report for moderate doses of LSD or psilocybin, muscle cramps were the strongest physical effect, and they named psychosis, dissociative disorders and bipolar disorder as reasons not to do it.
What it means. A breathwork class can be a far stronger experience than the word "breathing" suggests. This study did not test whether it helps anyone. What it adds is a sense of what kind of experience it is, and that the professionals who tried it singled out people prone to dissociation, and ranked post-traumatic stress lower than other anxiety, when asked who it suits.
Worth knowing. There was no comparison group, about half the therapists had done this kind of breathwork before, and the comparison with psychedelics is drawn against other people's studies rather than tested here.
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Environment and inputs
Twelve trials of magnesium for sleep disagree with each other, and the reviewers rate the evidence low
Magnesium is one of the most common supplements taken for sleep. This review gathered the randomised trials that tested magnesium on its own for sleep in adults, twelve in all, using different doses, forms and lengths of treatment. Results were inconsistent whether sleep was measured by asking people, by brain recordings or by wrist devices, and the reviewers rated their confidence in the evidence as low to very low.
What it means. The reviewers' own conclusion is that the evidence does not support magnesium as a routine treatment for insomnia, though some people in some trials reported modest benefits. If it seems to help you, this does not say otherwise. It says the trials have not shown it reliably.