Sleep, stress, and blood pressure: what WHOOP is studying now

Originally published on April 17, 2024

Sleep, stress, and blood pressure are tightly linked, and this article explains how WHOOP is studying that connection at scale. In Episode 268 of the WHOOP Podcast, Dr. Kristen Holmes, Global Head of Human Performance, Principal Scientist at WHOOP, joins Emily Capodilupo, Senior Vice President of Research, Algorithms, and Data at WHOOP, to break down a new member study that combines overnight physiology, morning blood pressure readings, and subjective stress reporting.

The conversation focuses on four questions: why blood pressure is central to the study, how the at-home protocol works, what the two-way relationship between sleep and stress looks like, and how WHOOP may use the results to separate circadian sleep issues from sleep anxiety.

To listen to episode 268 in full, head to the WHOOP Podcast on YouTube.

Why is WHOOP studying sleep, stress, and blood pressure together?

WHOOP is studying these three variables together because stress and sleep work in both directions, and blood pressure adds an objective signal that can help interpret what is happening overnight. Capodilupo explained that sleep can raise or lower your stress tolerance, while stress can change how easily you fall asleep and how your body moves through the night.

That framing starts with a public health problem. Capodilupo pointed to [National Institutes of Health stress resources and a long-running concern from the World Health Organization that chronic stress has become a major issue, yet many people still treat feeling stressed as normal background noise. Holmes and Capodilupo argue that this normalization is part of the problem. If stress is everywhere, people stop asking whether the level is appropriate for the situation.

WHOOP already measures several signals that can reflect how your body is responding to pressure, including overnight sleep patterns and daily stress trends. This study adds blood pressure because it gives the research team a practical way to compare subjective stress, wearable data, and a well-established physiological marker in the same protocol. That combination matters if the goal is to move beyond broad advice and toward coaching that fits the actual source of the problem.

The team also wants the study to be useful for participants, not only for future product development. Members who complete the protocol are expected to receive a personalized report on how their sleep and stress data related during the study window. That member-level feedback is a major reason this project sits naturally alongside Digital WHOOP Labs.

Capodilupo gave the clearest summary of the study premise when she said:

“Sleep impacts stress and is impacted by stress.”

That short line is what makes the design coherent. WHOOP is not treating sleep as a standalone behavior or stress as a standalone feeling. The study is designed to show how overnight physiology, morning blood pressure, and perceived stress can clarify one another. For related context on how WHOOP has examined stress and cognition before, see Episode 131 on stress, sleep, and cognitive functioning.

What you should take away

• WHOOP is pairing overnight wearable data with morning blood pressure readings to study stress from more than one angle.
• Blood pressure is included because it gives the study an objective marker that can be compared with sleep data and self-reported stress.
• The core research question is bidirectional: sleep can change stress, and stress can change sleep.
• Participants are expected to receive individualized feedback, not only contribute to a population-level analysis.

If you want to hear Capodilupo unpack why WHOOP chose blood pressure as the study’s primary endpoint, listen to the full episode on Youtube.

How does the WHOOP study protocol work for members at home?

Once the study goal is clear, the next question is practical. WHOOP built the protocol so eligible members can complete it at home in a short window, without visiting a physical lab. The basic design is three nighttime and morning pairs, usually spaced about a week apart, across 15 to 30 days.

Capodilupo said participants must be at least 18 years old, based in the United States, and able to use an FDA-approved blood pressure cuff. Each night session starts with a short survey about your day. You then sleep wearing WHOOP as usual. In the morning, about 30 minutes after waking, the app asks a few follow-up questions, then guides you through paced breathing and three blood pressure readings taken one minute apart.

That 30-minute gap after waking is there to let sleep inertia wear off before the blood pressure sequence begins. The morning instructions also matter. Capodilupo said the protocol asks participants to avoid eating, drinking, exercising, or using extreme heat or cold before the readings, because those inputs can change blood pressure and add noise to the dataset.

Holmes pressed on an important detail: how should members breathe? Capodilupo kept the rule simple. The team wants slow, intentional breathing that feels sustainable, not a style that adds effort or anxiety. Holmes suggested options such as a physiological sigh or slow breathing with a longer exhale. Capodilupo added that box breathing can also work for people who already use it.

The protocol is intentionally light. As Capodilupo put it:

“The sort of active part of the study is 2 minutes at night, it takes about 5 minutes in the morning.”

That time estimate matters because research participation often fails when instructions are too hard to fit into real life. WHOOP is trying to reduce that friction while still collecting enough structure to compare nights, mornings, and participant groups.

Capodilupo also cautioned against turning the one-minute waits into phone time. She referenced UC Irvine email apnea research suggesting that people often breathe more shallowly or briefly hold their breath while reading email. If the study is testing whether intentional breathing lowers acute stress markers, scrolling during the rest intervals would work against the protocol.

What you should take away

• The at-home protocol uses three night and morning sessions over roughly 15 to 30 days.
• Members need WHOOP, an FDA-approved blood pressure cuff, and a quiet morning window about 30 minutes after waking.
• The morning session asks participants to avoid food, drinks, exercise, and extreme heat or cold before readings.
• WHOOP designed the study to keep active participation under an hour across the full protocol.

For Holmes’s full take on how the study fits into Digital WHOOP Labs, listen to the full episode on Youtube.

How do stress and sleep affect each other from one day to the next?

The relationship is circular. Poor sleep lowers your capacity to handle stress the next day, and elevated stress can make it harder to fall asleep or stay in restorative sleep that night. Holmes and Capodilupo both described this as one of the main reasons the study matters.

Capodilupo’s explanation was simple and useful. When you are sleep deprived, the same event can trigger a bigger response than it would on a well-rested day. She described stress tolerance as a kind of reservoir that shrinks when you are tired. The result is familiar to most people: shorter patience, more irritability, and a stronger reaction to ordinary demands.

The other half of the loop shows up at bedtime. When stress becomes worry and rumination, it can delay sleep onset. Capodilupo argued that a large share of what people think of as a pure sleep problem is actually a stress problem that appears at bedtime. In practice, that means the solution may not be only about bedtime timing or sleep duration. It may also involve calming the mind enough to stop replaying the day.

Capodilupo pointed to research on writing worries down before bed, which she said can reduce the mental spin that keeps people awake. A brief end-of-day check-in, even on scrap paper, can be enough to give the brain closure. That idea aligns with earlier WHOOP reporting on sleep consistency and mental health and how sleep impacts performance, both of which show that sleep is tied to far more than fatigue.

Capodilupo made the point directly:

“A huge, huge percentage of what used to be thought of as sleep onset insomnia, so trouble falling asleep, is now understood to be a mental health issue. It’s stress.”

That is exactly why this study uses both subjective and objective measures. WHOOP is not only asking how long someone slept. The team is trying to see whether overnight patterns, morning stress perception, and blood pressure move together in ways that can separate a stress-heavy night from a timing problem, a behavior problem, or a one-off bad night.

For extra background on how objective sleep measurement supports this kind of work, see the earlier WHOOP sleep validation study.

What you should take away

• Poor sleep can lower stress tolerance the next day, making ordinary demands feel larger than they otherwise would.
• Stress can delay sleep onset by turning bedtime into a period of rumination rather than recovery.
• Short end-of-day practices, including writing worries down, may help reduce bedtime mental load.
• WHOOP is studying this loop so sleep disruption can be matched to its likely cause, not only its symptom.

If you want to hear Capodilupo go deeper on rumination, sleep onset insomnia, and why bedtime stress gets misread as a sleep-only issue, listen to the full episode on Youtube.

How could WHOOP use this study to coach sleep anxiety more precisely?

After establishing that sleep and stress affect each other, the final question is what WHOOP can do with that knowledge. The goal is not to drive stress to zero. The goal is to tell the difference between productive activation, excessive anxiety, and sleep problems that are really about circadian timing.

Holmes framed this as a perception issue as much as a physiology issue. A challenge can produce an appropriate rise in arousal that sharpens focus. A threat can produce a response that is too large for the moment. Capodilupo pushed the same point further, arguing that modern life creates many tiny, repeated activations that look nothing like a true emergency but still trigger the body again and again. Phone notifications, email, and constant interruption are examples she called out.

That distinction matters for coaching. Two people might show similar time in bed or similar total sleep, but one person may be dealing with circadian misalignment while the other is dealing with sleep anxiety. If the cause is different, the coaching needs to be different. Capodilupo said that current sleep guidance often focuses on timing and duration, but the next step is understanding when stress is the factor disrupting sleep.

The size of the study is part of that plan. WHOOP wants a large and varied group so the analysis can look across sex, training habits, high or low blood pressure, reproductive status, workout timing, and baseline sleep patterns. A small sample could miss those interactions. A broader sample gives the team a better chance of finding which combinations matter for whom.

Capodilupo also pointed to small interventions that can help people interrupt unnecessary activation during the day. She said:

“A minute of intentional breathing or 30 seconds of hero posing can make a measurable difference that lasts not just in the minute while you’re intentionally breathing, but hours after.”

That is a useful standard for interpreting the study. WHOOP is not only looking for dramatic stress events. The team is interested in whether small, repeatable behaviors can change the stress load that shows up in blood pressure and sleep. Read alongside the earlier WHOOP feature on Dr. Jemma King’s advice for managing sleep and stress at work, the message is clear: the future value is more specific coaching, matched to the kind of activation a person is actually having.

What you should take away

• WHOOP is trying to separate productive arousal from anxiety and from circadian sleep problems that need different coaching.
• A large and varied member sample is necessary because stress and sleep patterns change across behaviors, biology, and baseline health states.
• Small interventions, including brief intentional breathing, may lower activation enough to influence how stress carries into sleep.
• The practical goal is more precise guidance when sleep data looks similar but the underlying cause is different.

For Holmes’s full take on productive stress, sleep anxiety, and the kind of personalized coaching this study could support, listen to the full episode on Youtube.

The bottom line

• WHOOP is studying sleep, stress, and blood pressure together because each one can help explain the other two.
• Blood pressure gives the study an objective morning marker that can be compared with overnight wearable data and self-reported stress.
• The member protocol is built around three night and morning sessions, each with short surveys, overnight wear, paced breathing, and three blood pressure readings.
• Poor sleep can shrink next-day stress tolerance, while elevated stress can delay sleep onset and change how a night of sleep feels and functions.
• WHOOP researchers believe many bedtime sleep complaints may partly be stress complaints that show up as rumination and worry.
• The goal of the study is not zero stress, but a clearer distinction between productive activation, anxiety, and circadian sleep disruption.
• A large and varied member sample helps WHOOP study how sex, training, blood pressure, and baseline sleep patterns change the sleep-stress relationship.
• The long-term value of this research is more specific coaching when two people show similar sleep data for very different reasons.

Frequently asked questions about things discussed in this episode

How does WHOOP study stress during sleep in this research?

WHOOP studies overnight stress by combining sleep data from WHOOP, short evening and morning surveys, and a morning blood pressure sequence to compare subjective and objective signals.

What does WHOOP ask members to do in this study?

WHOOP asks eligible members in the United States, age 18 or older, to complete three night and morning sessions over 15 to 30 days while wearing WHOOP overnight and using an FDA-approved blood pressure cuff in the morning.

How does WHOOP use blood pressure in the protocol?

WHOOP uses blood pressure as an objective marker of acute stress during a guided morning breathing window, with three readings taken one minute apart.

What does WHOOP do if sleep problems are really stress problems?

WHOOP uses this kind of research to identify whether sleep disruption may be tied to anxiety and rumination rather than only bedtime timing, so future coaching can better match the cause.

How does WHOOP think about productive stress versus harmful stress?

WHOOP treats stress as useful when it matches the demand of the moment and helps focus, and as harmful when activation stays too high, too often, or continues when the situation no longer requires it.

What can WHOOP members learn from joining this study?

WHOOP expects participants to receive a personalized report on how their sleep and stress data related during the study period, alongside the broader findings released after analysis.

For people trying to sleep better without guessing, this WHOOP research is aimed at showing when overnight physiology points to anxiety, when it points to timing, and when it points to a stress load you can actually change.