#154 - Sleep and Cortisol

Matt Walker (0:02)

Hi there, and welcome back to the podcast, it's Matt here. Today, I want you to imagine a little plastic tube, about four inches long, and inside the tube is a swab. And the directions for using it are pretty specific. When you first wake up, stick it in your mouth, let it soak, put it back in, and write down the time. 30 minutes later, do another sample. Then a third sample at 45 minutes. It has to be exact, because if not, you've broken the protocol. These tubes are given to thousands of research subjects across the globe because a vial of saliva upon waking up is a common way for us to measure our levels of stress hormones. And currently, this hormone is the villain on social media for many things, from weight gain, to a puffy face, late night awakenings and more. And now you can buy Cortisol detox products, Cortisol face videos, Cortisol lowering supplements, etc. So maybe the most straightforward question to ask is, is Cortisol bad for you? Well, the answer is more complicated than the Internet suggests. And if the allegations against this chemical are to be believed, they deserve to be addressed. So let's investigate the benefits and the drawbacks of Cortisol. We will hear the case for and against, and after we will issue a verdict. Not a split decision either, because the truth is actually fairly clear on the matter, and it's not what the Internet would lead you to believe. The first point to consider is something that rarely comes up online. You need Cortisol to survive. When the body cannot make enough of it, the result is a condition known as adrenal insufficiency. Or when the adrenal glands themselves are the thing that has failed, Addison's disease. It is life-threatening, and the endocrinology literature is consistent on the point that early recognition and treatment are what prevent serious harm and death. And how does a person treat Addison's? By providing them with the missing hormone. The Endocrine Society has published an entire set of guidelines on how to replace Cortisol in patients suffering from the disease. Cortisol's usual functions, as it happens, have surprisingly little to do with panic. In normal background amounts, it acts permissively. It helps keep metabolism, blood pressure regulation, and immunity running smoothly, maintaining a supply of glucose, and general readiness to act.

So, what about the release schedule? Imagine a small office with two telephones feeding in, and one secretary taking both calls. On a regular daily basis, regardless of whether there is any news, the first phone rings. The second phone only rings whenever something actually happens. The secretary answers both, and relays the same message either way. That office is the HPA axis, or Hypothalamic Pituitary Adrenal Axis, which is the main system your body uses to react to stress. And much of this trial depends on it having precisely those two inputs. One line is a clock, the biological rhythm that causes the daily cycle of cortisol release, regardless of whether anything stressful ever happens. The other line is an alarm, stress response, calling upon the system to secrete more cortisol on demand. The message is always the same. Mobilize resources to meet the need, whether the need is real or anticipated. One final opening point for the defense. Cortisol receptors exist in numerous organs and tissues throughout the body, and via them, the hormone alters the functioning of many systems in the interest of keeping the internal environment stable. In effect, it acts as a master signal for the whole body. Incidentally, this is the prosecution's strongest piece of evidence. A signal that so many things respond to is exactly the type of molecule whose lack and whose permanent overproduction would both cause problems everywhere at once. And here is the defense's star witness. The shape of your day.

If you plot cortisol levels during the course of a day, you get one of the most robust rhythms in human biology. Low levels in the evening and the first part of the night, rising through the latter half of the night, peaking around the time you normally wake, with a last push in the half hour after you get up. This daily pattern was mapped in fine detail more than 50 years ago when researchers took blood samples every 20 minutes round the clock and saw the same regular rhythm playing out again and again. Healthy men were equipped with a sampler that reads Cortisol continuously. The data showed the Cortisol trough aligns with sleep onset, and the Cortisol peak aligns with waking in everyone. Put the wearable version on 214 volunteers, and you see the same pattern again, only sampled in the tissues of the body. And this isn't something that sleep generates en route. Mistime a person's sleep experimentally, and the plasma Cortisol rhythm largely stays where it was, running to the clock rather than to the sleep. During the first 30 to 45 minutes after waking, Cortisol rises steeply again, and that rise is distinct enough that it's got its own name. The Cortisol Awakening Response and its own guidelines for measurement, which is why there are the three timed spit tubes. Most of the days Cortisol in healthy people is secreted in the hours either side of morning awakening. Take a minute to digest that. If this is damage, your body is doing a good deal of it to itself over breakfast. The more plausible explanation is that the rise is preparatory.