Contributed by Sofie Jacobsen, M.S.
The holiday season is upon us.
This time is filled with joy, loved ones, and overindulgence. Merry celebrators tend to drink and eat a bit more, and a bit closer to their bedtime, than usual. And with the time crunch of prepping for everything, you may be tempted by a late-night workout to try and fit everything into one day.
At Eight Sleep, we wanted to understand how late-night eating, drinking, and exercising affect the best gift of all, sleep. We studied 90 men and women ages 45+ across 1,770 nights who slept with Pod temperatures on vs. off for 1 week each, and completed morning surveys about their eating, drinking, and exercise behaviors the previous night.
Bad news: We found that eating, drinking, and exercising within 3-4 hours of your bedtime negatively affects your sleeping heart rate (HR) and heart rate variability (HRV) recovery during sleep.
Good news: The Pod helped reduce the negative effects of these behaviors.
Key takeaways
When people were not using the Pod’s temperature regulation features, we saw the following changes:
- Late meals (within 3 h of bedtime) raised HR by 3% and lowered HRV by 7% on average, but these effects disappeared when people slept with Pod temperatures on.
- Alcohol (1-2 drinks within 4 h of bedtime) increased HR by 7% & decreased HRV by 13%.
- Intense workouts (within 1.5 h of bedtime) raised HR by 2%, but this negative effect disappeared when sleeping with Pod temperatures on.
Having a lower HR and higher HRV at night are signs that your body is recovering well (source, source). When your HR stays higher or your HRV is lower than usual, it suggests your body hasn’t fully bounced back yet. Nighttime HR and HRV are essentially a report card on how well you’ve recovered from recent days and how prepared you are for the day ahead.
Eating right before sleeping means you may pay a recovery tax
Strong cardiovascular recovery during sleep is typically defined by a low HR and a high HRV. Our past studies have shown that sleeping on the Pod alone decreases HR by 3% and increases HRV by 11% (source). Unfortunately, eating within 3 hours of bedtime negatively impacts cardiovascular recovery, such that we see higher HR and lower HRV (see Fig. 1). With Pod OFF, nights that members reported eating within 3 hours of bedtime were associated with a 3% higher HR and 7% lower HRV, compared to non-drinking nights. However, sleeping with Pod temperatures ON cancelled out the negative effects of eating before bed: HR and HRV had no significant changes from baseline compared to nights without late-night eating (average HR % change: 0%; HRV % change: 4%).
These data show that when you’re away from the Pod, you should avoid eating within 3 hours of bedtime for optimal cardiovascular recovery. But if you’re sleeping on the Pod, you don’t have to worry too much about those late-night meals– the Pod will help.
Figure 1. Average percent changes in heart rate (HR) and heart rate variability (HRV) relative to individual baseline (i.e., no eating within 3 hours of bedtime when Pod OFF). The changes in HR & HRV are split based on sleeping with Pod temperatures ON vs. OFF. Error bars show standard errors. Blue indicates no eating within 3 hours of bedtime, while orange indicates eating within 3 hours of bedtime.
Raising a glass impairs your cardiovascular recovery, though the Pod softens the blow
Similar to previous research (source, source), we found that indulging in alcoholic drinks within 4 hours of bedtime is bad for cardiovascular recovery. And the effects compound: the more you drink, the worse your cardiovascular recovery (see Fig. 2 and Table 1). However, sleeping on the Pod after drinking can dampen the negative effects. Specifically, we found that sleeping on the Pod cancelled out the effect that 1-2 drinks before bedtime had on HRV.
Therefore, if you want to help optimize your cardiovascular recovery during the holidays, consider cutting back on the number of drinks, or drink more than 4 hours before you go to bed. And if you get caught up in the festivities, your Pod can help minimize these negative effects.
Table 1. Alcohol’s effect on cardiovascular recovery
| 1-2 drinks, Pod OFF | 1-2 drinks, Pod ON | 3-4 drinks, Pod OFF | 3-4 drinks, Pod ON | |
| % change in sleeping HR from baseline | +7%* | +4%* | +16%* | +10%* |
| % change in sleeping HRV from baseline | -13%* | -3% | -33%* | -13%* |
Note. How alcohol within 4 hours of bedtime impacts your heart rate (HR) and heart rate variability (HRV) with the Pod’s temperature regulation on (Pod ON) vs. off (Pod OFF). Average percent changes are relative to each individual’s baseline (i.e., no drinking within 4 hours of bedtime during Pod OFF). * indicates a statistical difference to baseline (P<0.05).
Figure 2. Average percent changes in heart rate (HR) and heart rate variability (HRV) relative to individual baseline (i.e., no drinking within 4 hours of bedtime during Pod OFF). Data are split by changes in HR & HRV when sleeping with Pod temperatures ON vs. OFF. Error bars reflect standard errors. Light blue indicates no alcohol within 4 hours of bedtime, dark blue indicates 1–2 drinks, and orange 3–4 drinks within 4 hours of bedtime.
The Pod can help stabilize your overnight cardiovascular recovery after a late-night training session
While hitting the gym is generally good for you, you might want to reconsider HIIT workouts within 1.5 hours of bedtime.
When sleeping with Pod temperatures OFF, we found that HR increased by 2% when doing an intense workout vs. not working out within 1.5 hours of bedtime. However, this negative effect was cancelled when members slept with their Pod temperatures ON after completing high-intensity workouts within 1.5 hours of bedtime (mean HR % change of -2%).
These data indicate that you should avoid high-intensity exercise within 1.5 hours of bedtime when sleeping off the Pod. But when sleeping on the Pod, don’t worry about it– the Pod can still help you recover optimally.
Figure 3. Average percent changes in heart rate (HR) and heart rate variability (HRV) relative to individual baseline (i.e., no high-intensity workout within 1.5 hours of bedtime during Pod OFF). Data are split for HR & HRV changes when sleeping with Pod temperatures ON vs. OFF. Blue indicates no workout within 1.5 hours of bedtime and orange indicates intense workouts 1.5 hours before bed.
So what can you do to improve your cardiovascular recovery this holiday season?
- Avoid or reduce snacking and meals within 3 hours of bedtime.
- Avoid or reduce alcohol within 4 hours of bedtime: consider knocking back the eggnog a little earlier in the day or, even better, swap it for a non-alcoholic version.
- Avoid intense workouts within 1.5 hours of bedtime. If exercising close to bedtime, swap the high-intensity workout for something lighter- a brisk walk, yoga, or any activity where you can comfortably hold a conversation.
And if not everything goes according to plan, the Pod has got your back! Happy holidays from all of the Eight Sleep team.
Appendix
Our 90 members slept with their Pod temperature regulation on (Pod ON) vs. off (Pod OFF) for one week in each condition while wearing Oura rings to measure their HR and HRV. On each morning, members completed a brief survey about their eating, drinking, and exercise the prior evening. The survey included questions about the time of their last meal, the timing and amount of any alcoholic drinks, and any exercise the previous day. We then looked at how close these behaviors were to their normal bedtimes. We linked these bedtime behaviours to their HR and HRV during both the Pod ON and Pod OFF week. We normalized the nightly HR and HRV to each user’s unique baseline (Pod OFF nights without the bedtime behavior being tested) before analyzing. For example, we compared no bedtime eating with the Pod OFF to eating before bedtime with the Pod ON to understand how the Pod could help members enjoy their steak dinner and still rest their heart.
These findings were part of a larger study aimed at understanding how sleep changes with age. Nights were excluded from analysis if subjects either slept less than <4 or >14 hours or had an irregular sleep composition. A night with irregular sleep composition was a night where one or both of the following were true: (1) Wake after sleep onset (WASO) was greater than 2.5 standard deviations away from the subject’s mean during the study. (2) any sleep stage (deep, light, or REM) percentage(s) was/were greater or less than 2.5 standard deviations from the subject’s mean during the study. These exclusions left 1,770 nights for analysis. Subject mean HR or HRV for the Pod OFF condition with no late-night eating, drinking or exercise was used as the baseline to compare percent change in HR or HRV based on shifts in Pod condition (ON/OFF) and pre-bedtime behaviours. All means and standard errors plotted are extracted from linear mixed effect models, reflecting the mean change in HR and HRV expected across subjects on individual nights. Standard errors were adjusted using CR2-adjustments to account for influential nights.
