Most sleep advice is a list of twenty things. The evidence points at a much shorter list, and the first two do most of the work.
1. The same bedtime and wake time, most days
Sleep timing is an anchor for your body clock. Shifting it around, even with the same total sleep, leaves you feeling worse and shows up as lower HRV and higher overnight heart rate. Pick a wake time you can keep on weekends and let bedtime follow. Sixteen scores consistency as its own part of the sleep score, so you can see the drift before you feel it.
2. A hard stop for the phone
Carter and colleagues’ 2016 meta analysis found that bedtime use of portable screens was associated with shorter sleep, poorer sleep quality and daytime sleepiness. Exelmans and Van den Bulck found the same in adults: later bedtimes, longer time to fall asleep, more fatigue. The mechanism is partly light, mostly content. A feed is designed to keep you scrolling, and it does.
The fix that works is a rule that enforces itself. Sixteen locks the apps you choose at the start of your sleep schedule and keeps them locked until morning. The last thing before bed becomes a book, a conversation, or the ceiling.
3. Caffeine before early afternoon
Caffeine has a half life of around five to six hours. A coffee at 4pm is a quarter coffee at 10pm. Move the last one to early afternoon and see what the score does over a week.
4. Alcohol earlier, or less
Alcohol makes you fall asleep faster and then fragments the second half of the night. Overnight heart rate goes up, HRV goes down, and sleep stress, the part of the Sixteen score that watches your vitals through the night, shows it clearly.
5. Cool, dark, quiet
A bedroom around 18 degrees Celsius, a room as dark as you can get it, and something to cover unavoidable noise. Boring, but it is the physical environment your body clock expects.
6. Light in the morning
Bright light soon after waking sets the clock for the following night. Outside for ten minutes is better than any lamp.
7. Move during the day
Regular exercise improves sleep quality and depth. Very hard sessions late in the evening can delay sleep for some people; finish them a few hours before bed if your score suggests it.
What to try first
If you change one thing, make it the screen curfew. If you change two, add a fixed wake time. Give each a full week, watch the seven day sleep score, and log the change in your journal so you can tell what caused what.
Sources
- Hirshkowitz M et al. National Sleep Foundation's sleep time duration recommendations: methodology and results summary. Sleep Health, 2015.
- Carter B, Rees P, Hale L, Bhattacharjee D, Paradkar MS. Association between portable screen based media device access or use and sleep outcomes: a systematic review and meta analysis. JAMA Pediatrics, 2016.
- Exelmans L, Van den Bulck J. Bedtime mobile phone use and sleep in adults. Social Science and Medicine, 2016.
