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Cortisol has earned a reputation as a, well, “stress hormone.” 

But cortisol itself is just misunderstood. Sure, too much of it certainly has negative effects — it can,  for example, hamper our immune system and raise our blood pressure — but the hormone is an important tool for our bodies to prepare for and deal with stress. What’s more, its effects on our metabolism and ability to boost blood sugar make it an energizing chemical. Quite simply, it gives us pep.

This is important, because the release of cortisol is tied to our circadian rhythm, with the hormone’s levels naturally jumping when we wake up in the morning. This is the so-called Cortisol Awakening Response (or CAR) — an important and often-overlooked part of waking up.

“It’s likely there to prepare you for the challenges of the coming day and to give you a boost of energy,” says Luis de Lecea, Ph.D., a professor of psychiatry and behavioral sciences at Stanford University. “This is a natural response that peaks about 30 minutes after waking up.”

If you have a big day ahead of you (maybe there’s something you’re looking forward to?) and find it particularly easy to wake up that day, the CAR could be partially responsible. But the CAR—like almost anything involving hormones—is also a highly fragile process. If your morning cortisol levels are too high, you could be at risk for high blood pressure or diabetes. But if they go too low, you’ll likely face a host of other problems.

“People with a deficient CAR may have deficient levels of energy—or may not even be able to wake up at all,” says Raj Dasgupta, MD, an associate professor of sleep medicine at the University of Southern California and a fellow of the American Academy of Sleep Medicine.

It’s also a highly influenceable process, with research suggesting that numerous factors—including many that are well within our control—can impact whether or not we have a healthy CAR. For example, waking up early in the morning tends to result in an increased CAR, while sleeping in the presence of pervasive low-frequency noises (think: traffic and other sounds of the city) can seriously dampen it. Other factors that have been shown to dampen CAR include fatigue and sleeping while in pain, while wakening in sun-like light as opposed to pitch black — is associated with an increased CAR.

According to Dr. Dasgupta, the hormonal shifts that can result from such ambient and environmental factors suggest that many people are looking at healthy sleep the wrong way. In particular, people are often concerned about how to fall asleep, but neglect the factors that are important to maintaining high-quality rest once they’ve fallen asleep.

“Me and you could each sleep eight hours, but is that eight hours of quality sleep?” says Dr. Dasgupta.

“When people ask me if you can die from poor sleep, I say that of course you can die. You can have a car accident, but there are also the long-term effects: Heart attack, diabetes, high blood pressure. And your cortisol levels are an important marker for these.”

And while the CAR is an important factor in our ability to wake up with energy, it’s also important to view cortisol as part of a larger hormonal machine.

“There are literally hundreds of signals in brain that put you in alert, and cortisol is just one piece in a very complex puzzle,” says de Lecea.

But if you constantly wake up feeling groggy, trying to influence it through changes to lighting, noise and wake times can be a good place to start.