A long nap can make it harder to fall asleep at night. Naps reduce sleep pressure, which can delay sleep onset, even if your circadian rhythm is promoting it. Sleep regulation is a complex interaction between circadian, sleep pressure, and prior sleep.

Exercise increases the rate of sleep pressure build up. This is part of why you may want to go to bed earlier after a hard training day.

We’re in a scientific age of 2nd (+) order consequences. It’s no longer just A impacts B, but rather how much impact and when.

Sleep and circadian rhythms respond to different inputs. Sleep pressure builds with time awake and can be relieved by sleep or naps. Circadian rhythms respond to light. Optimizing means using both inputs to align your physiology.

Sleep and circadian rhythms are connected, but not the same. While sleep timing and architecture can be influenced by circadian, homeostatic pressure is the main lever. Recognizing the difference helps explain jet lag, shift work, and why good sleep isn’t just about duration.

It’s solstice week. The longest stretch of daylight of the year happens in the Northern Hemisphere this Friday. At 7:42 PM PT, the sun reaches its maximum northern declination, marking the summer solstice.

Around the solstice, the sun’s position at solar noon barely changes day to day. Early observers noticed this and aptly named it solstice, from the sun (𝘴𝘰𝘭) standing still (𝘴𝘪𝘴𝘵𝘦𝘳𝘦).

The solstice does not always align with the earliest sunrise and latest sunset of the year. This year in Palo Alto, earliest sunrise was on June 13th and the latest sunsets will be on June 26th & 27th, but the solstice is on June 20th.

It’s solstice day. The more north you are, the more unsettling it is. Some regions don’t even have night. Remember, the key to circadian alignment is balance between phase advance and phase delay. Not pure duration of exposure. Stay aligned folks.

New moon tonight 0% illuminance but keep your shades shut bc other sources of light pollution can still impact sleep

Out today in PNAS, we explore how sleep habits – and nightly changes in sleep – may link to next-day physical activity. In two large-scale wearable sensor studies (~6.5 million nights from ~26,000 individuals), we found: 1. Longer sleep duration and later sleep timing were

I’m pretty skeptical of language encoding enough info to produce AGI. There’s so much processing in other hidden signals of the body that contribute to the human experience and intelligence. Language has reduced dimensionality.

I'm thrilled to share our new study out in Nature Medicine! We show that a blood test can estimate how aged or youthful one’s organs are and that these organ ages predict future disease and lifespan. Final paper from my PhD in the Tony Wyss-Coray lab. 🧵1/12 🔗 nature.com/articles/s4159…

Daylight savings time and time policy are at peak antimemetic state rn

Your chronotype impacts your life beyond your preferred behavioral timing. It can influence assortative mating. You might meet (and mate) with someone with a similar chronotype simply because there is more temporal overlap.

In reality, this would not “skip” jet lag. Launching into space is independent of the changes in light diet that trigger jet lag.

Jet lag can disrupt the menstrual cycle. We don't know exactly how this occurs, but don't be surprised if your cycle is a little longer or shorter than normal following travel.

Big opportunity here for airlines to implement circadian lighting based on flight timing, duration, and time zones between destinations. We have the science/engineering to support at this point.

Love this diurnal clock representation. Next let’s do the circadian clock.

Even if we could collect all of these simultaneously, which would take a lot of power for a wearable, the bottleneck is not in collection. It’s in the interpretation.