Why Some Cities Can't Wind Down

Ask most people what they know about cortisol, and you'll get some version of the same answer: high cortisol is bad. It means you're stressed. You should try to lower it.

That framing is understandable—it has been especially prevalent in our culture recently—but it's missing something important. When we looked at a year's worth of cortisol data across 15 US and Canadian cities,¹ the picture that emerged was more nuanced, and more interesting, than the simple "high cortisol = stressed" mindset many of us have been operating under.

The cities with the highest morning cortisol often recovered best. The cities with the flattest curves didn't. 

Here's what the data showed—and what it means for how you think about your own stress response.

Key takeaways

• A strong morning cortisol spike is healthy: it indicates your nervous system is well-regulated.²

• The diurnal ratio matters more than one number alone: the difference between your morning peak and your evening floor tells you whether your stress system is recovering. A healthy range is roughly 1.5× to 3.0×.³

• Among the 15 cities sampled, Tucson had the strongest recovery curve (3.10×) and New York had the flattest (1.32×).

• Environmental factors like sunlight, light pollution, commute time, noise, and access to nature may help explain why some cities recover and others struggle to.

What your cortisol is actually supposed to do

Cortisol follows a rhythm. Every morning, within 30 to 60 minutes of waking, your body produces a sharp spike in cortisol called the Cortisol Awakening Response (CAR). This isn't a stress reaction—it's a preparation signal: your body mobilizing energy, sharpening focus, and stabilizing blood sugar so you're ready for the demands of the day.

A strong morning spike is a good thing. It indicates your HPA axis (the hypothalamic-pituitary-adrenal system that governs your stress response) is working the way it should.

But you can't gauge how well you're recover from morning cortisol alone.  What happens next is equally important.

After peaking in the morning, cortisol should gradually decline through the day, reaching a low floor by evening. That decline—from morning peak to evening floor—is called your diurnal ratio. Research shows that in healthy individuals, cortisol typically drops 70–80% from morning to evening. When this pattern is disrupted and the curve starts to flatten, your stress system never gets the signal that the day is over. 

A healthy diurnal ratio sits in the range of roughly 1.5× to 3.0×. A flat curve, where morning and evening cortisol are nearly equal, may be a more meaningful early signal of chronic dysregulation than a high morning reading alone.

What we found across 15 cities

We analyzed morning and evening cortisol readings across 15 major cities in the US and Canada, filtering the sample size to at least n ≥ 30 and applying a 5% trimmed mean to both ends to reduce the effect of extreme values.

One pattern came through clearly: some cities wind down at night. Others stay wired.


 

At the top of the dataset, Tucson led with a diurnal ratio of 3.10×—a strong morning peak that fell sharply by evening. Close behind were San Francisco (2.39×), Oakland (2.29×), Austin (2.20×), and Calgary (2.10×), which all showed healthy morning-to-evening drops well within the 1.5–3.0× range. The middle of the pack included Los Angeles, San Diego, Montreal, Houston, Toronto, and Seattle, which ranged from 1.53× to 1.71×, indicating moderate recovery. Chicago and Miami tied at 1.41×. At the bottom sat Brooklyn (1.37×) and New York (1.32×), the flattest curves in the dataset with cortisol that barely declined between morning and night.

The counterintuitive finding

Here's what surprised us most: the cities with the highest morning cortisol were often the ones with the strongest recovery curves.

Tucson and Calgary both showed elevated morning cortisol: Tucson at 3.42 ng/mL and Calgary at 3.40 ng/mL, but their evening levels fell sharply to 1.05 and 1.54 respectively, producing strong diurnal ratios. New York and Brooklyn, by contrast, showed moderate morning cortisol of 2.76 and 2.25 ng/mL that barely declined by evening. They landed at 1.98 and 1.57 respectively.

Among the values in this dataset, a high morning cortisol reading wasn't the yellow flag, but a flat curve was.

Why do these cities differ?

We can't draw conclusions from this observational dataset alone, but independent research points to several factors known to influence cortisol rhythms—and they differ meaningfully between a city like Tucson and one like New York.

• Sunlight exposure → Tucson averages over 300 sunny days per year, which is well above the U.S average of 205. Morning sunlight is one of the strongest biological cues for a healthy Cortisol Awakening Response.⁴ In dense urban environments, factors like subway commutes, lots of indoor time, and overcast winters limit that exposure from the start of the day.

• Artificial light at night → Research links nighttime light pollution to disrupted cortisol rhythms and flatter diurnal curves.⁵ New York's 24/7 ambient glow can keep the nervous system in a state of low-level activation well into the night. Tucson, in comparison, is surrounded by designated dark-sky areas, which can help the body to properly downshift.

• Commute time and load → New York City commuters spend an average of 40.6 minutes each way in transit, the longest of any US city (and nearly double Tucson's 21.7-minute average.)⁶ Commuting in crowded, unpredictable, high-stimulation environments is a documented cortisol trigger⁷ that can keep the nervous system in alert mode well into the evening.

• Noise at night → Environmental noise activates the HPA axis and elevates cortisol.⁸ An estimated 2.65 million New York City adults report noise-disrupted sleep at least once per week, which can come from subways, sirens, and street traffic.⁹ Tucson's lower density means most residents sleep in genuine quiet, allowing cortisol to fall to a proper floor overnight.

• Access to nature → Tucson is flanked by Saguaro National Park and hundreds of miles of accessible trails. Research shows that as little as 20 to 30 minutes in a natural setting is associated with reductions in cortisol levels.¹⁰ For most New Yorkers, that kind of access requires intentional planning—making it a weekly event at best, rather than a daily reset.

These are plausible contributing factors supported by independent research, not conclusions drawn from Eli's dataset alone.

What this means for your cortisol

Wherever you live, the takeaway from this data is a simple question:

Does my cortisol actually come back down?

A flat curve where morning and evening levels that barely differ may be a more meaningful early signal of chronic cortisol disruption, rather than a high morning reading alone.

Your environment is working on your hormones, whether you notice it or not. Your commute, your exposure to morning light, the darkness of your bedroom, the noise outside your window aren't minor lifestyle variables. They're biological inputs that shape the rhythm your body runs on every day.

Eli's Hormometer™ lets you measures your personal cortisol curve so you get the full picture, not just a snapshot. Understanding your diurnal ratio is one of the most direct ways to examine whether your body's stress system is actually recovering.