Newsletter #300

Depressive disorders are the sixth most costly health condition in the US, costing an estimated $71 billion, And it is not an easy problem to solve, as a huge percentage of people with depression are unresponsive to antidepressant drugs.

Part of the challenge is that we still don’t fully understand the biological underpinnings of low mood, though we have made some progress in this area. As you might recall, we have previously discussed in this newsletter how inflammation and depression often seem to accompany one another. And some longitudinal research suggests that the former may drive the latter. For instance, British civil servants who started out with higher CRP levels were more likely to go on to be diagnosed with depression 12 years later, while those who entered the study with depression were not prone to experiencing elevations in inflammatory markers. Furthermore, a number of trials have shown that anti-inflammatory treatments, as well as omega-3 fatty acids, may improve depressive symptoms in some patients.

Now, this month, researchers at UCSF published an intriguing analysis suggesting that elevated body temperature (within a normal range) may be linked to depression. To learn more, and what we might be able to do about it, scroll down 👇🏽

Prior research has suggested that depression is linked to alterations in body temperature. A small cross-sectional study comparing outpatients with depression to normal controls found that temperature readings could often identify the depressed subjects, and participants with a temperature above 98.3° F were 2.6-fold more likely to belong in the depressed group.

To examine this association in a much larger cohort, researchers affiliated with UCSF cleverly took advantage of data from the TemPredict Study, a large-scale global study that started back in March 2020. You might remember hearing about this one back when it was being conducted. This study collected data from Oura Ring users, and followed participants over time to see if changes in body temperature could predict the onset of COVID-19.

Anyway, for this study, the researchers looked at skin temperature data from more than 21,000 Oura Ring users. Participants also completed monthly surveys related to symptoms of depression. In addition, another sample group of around 21,000 people took their temperature orally every day, and reported the results through an online survey. This group also provided monthly reports on depressive symptoms.

So, needless to say, this is a ton of data points to look at, compared to previous research in this area! Furthermore, because Oura Rings can take temperature readings every minute, the researchers were able to analyze that data to see if variation in body temperature throughout the day (and night) influenced depressive symptoms.

Indeed, the researchers determined that in both groups, higher body temperature was correlated with higher scores in the depression inventory (shown on this graph in their average PROMIS T-score). This association remained even after adjusting for demographic factors that can predictably influence body temperature.

Moreover, the Oura Ring data revealed that individuals with severe depressive symptoms exhibited less difference in their body temperatures from when they were awake versus when they were asleep. Normally, your body temperature fluctuates throughout the day in alignment with your circadian rhythm, but this natural oscillation seemed to be attenuated in individuals experiencing more depressive symptoms.

So what can be done about this?

It's sort of hard to say, because we don't necessarily know what is eliciting this change in body temperature. Could it be due to a rise in heat production due to metabolic processes (like fighting an infection or some other source of inflammation)? Or, on the opposite end, is it an issue with the body's natural cooling responses?

But one way that you can rapidly target the thermoregulatory systems of the body is through exposing the body to high heat, which triggers cooling processes in the body that lead to a rebound effect, wherein body temperature actually drops lower than before.

Notably, this effect has been demonstrated clinically in some small trials — whole-body hyperthermia treatment using infrared lamps was found to reduce depressive symptoms, with larger antidepressant effects in individuals who entered the trial with higher body temperatures. Other ways to achieve this effect, of course, might include warm baths, hot showers, hot yoga, exercising in the heat, etc.

Finally, timing may be relevant here. You can imagine that heat exposure later in the day, or even shortly before bed, might have greater benefits with respect to biological rhythms, as well as enhancing sleep quality as we’ve addressed previously on the podcast.

Limpets are fairly unassuming-looking molluscs that happen to be equipped with the strongest teeth in the animal kingdom. Indeed, these teeth seem to be among the toughest materials in the entire world.

Previously, spider silk ranked at the top of natural materials, in terms of tensile strength. But when researchers tested how much force that limpet teeth can sustain without breaking, the snail came out on top. These critters apparently use their teeth to literally scrape rocks for tasty bits of algae, so I guess they need to be extra tough in order for them to survive.

Given that these teeth surpass the strength of Kevlar, you can imagine that an effective duplication of this material could be quite useful.

Photo: University of Portsmouth

Supplemental melatonin is fantastic for helping realign your circadian rhythm, especially if you’re battling jet lag or adjusting to time changes (Daylight Saving Time is less than a month away!). But it’s important to source melatonin carefully, because quality control for over-the-counter supplements can be really questionable.

In one study, researchers systematically analyzed the actual melatonin content in 31 supplements purchased from groceries and pharmacies, and they found that melatonin content varied from −83% to +478% of labeled melatonin, and 70% had a melatonin concentration that was ≤ 10% of what was claimed!

That’s why you want to make sure to get a supplement that is independently lab-tested, like Nature Made. As an added bonus, this brand is super easy to find in stores.

This guide addresses five main categories for sleep optimization:

The key takeaway from this guide is that what you do during the day may be just as important as your nighttime routine for establishing healthy sleep.

And we capture some research-based strategies for coaxing your body to fall asleep, which take advantage of some of the thermoregulatory mechanisms that we alluded to earlier. For example, did you know that making your feet warm can help? Believe it or not, participants who wore socks to bed fell asleep 7.5 minutes faster and slept 32 more minutes, compared to controls who had bare feet.

Wishing you the best,

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