Resting heart rate and HRV shift with the seasons, and less so with age

If you track your resting heart rate or heart rate variability, you probably compare this week with last week. A new study suggests the calendar deserves a place in that comparison too.

The paper, published in npj Aging on October 31, used one year of continuous wearable data from 16,415 adults in the United States. That adds up to almost 5.9 million person-days. Most of the authors work at WHOOP, which paid their salaries and provided the data infrastructure. The others are at universities and an academic hospital.

There is one caveat about our reading. The version online so far is the abstract and author details, so every number below comes from that summary.

A summer and winter pattern

Both measures followed a clear yearly cycle. Resting heart rate was lower in summer than in winter. Heart rate variability was higher in summer than in winter.

The swings were modest. From peak to trough, resting heart rate moved by about 2.0 beats per minute, and heart rate variability by about 4.2 milliseconds.

Those numbers are small for one person on one morning. But they are in the same range as the changes people often read meaning into from week to week. A slow drift across autumn could look like a trend in your habits when part of it is the season.

Not mostly activity or sleep

The obvious guess is behavior. People move more in summer, and sleep shifts with daylight. The team tested both.

Physical activity and sleep each accounted for less than 10% of the seasonal pattern. The authors conclude that other factors are mainly responsible. The abstract doesn't say which ones, and we won't guess.

Smaller swings with age

The size of the seasonal swing wasn't the same for everyone. It was smaller in older adults than in younger ones, by about 29% and 48% for the two measures. Sex made no difference.

The swing was larger in people who were more active and had a lower BMI. The authors read this as a sign of greater cardiovascular plasticity, meaning a system that adjusts more to its surroundings. That is their interpretation of an association, not a tested cause.

A few limits are worth keeping in mind. The participants were people wearing a consumer tracker for a year, not a random sample of the population. And a seasonal pattern averaged over thousands of people tells you less about any single person's year.

Where Soma fits

Soma is a general wellness product, not a medical device, and it doesn't diagnose anything. In the Soma app, which isn't available yet, the Mind score reads HRV, resting heart rate and breathing against your own usual range. This study is a useful reminder that a usual range can drift over a year for reasons that have little to do with last week. That's why we care about comparing like with like. Soma Axon, the pod we are still building, uses the same light, cameras and stance every week, and shows each value with its margin of error, so a change over time is easier to trust. We wrote more about that in The same instrument, every week.

Sources, as of November 1, 2026: Jennings, Jenkins, von Hippel and colleagues, npj Aging. This post describes research and isn't medical advice.