Sleep Sub-study FAQ

What is the purpose of this research?

The purpose of this research study is to use wearable devices (Fitbits) to objectively monitor sleep and evaluate the impact of sleep behaviors on blood markers for cardiovascular and metabolic health. The study is funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health.

What is expected of me during this study?

You will be asked to:

  • Complete a short online questionnaire on your sleep habits.
  • Wear an NHS3-provided Fitbit for 14 consecutive days, including while you sleep.
  • Share your Fitbit data via Fitabase, an online platform that delivers your sleep data to our research team.
  • Keep a paper sleep diary for 14 days and mail it back at the end of the study.

Can I use my own Fitbit if I already own one?

Please use the NHS3-provided Fitbit during the study period. If you also wear a personal Fitbit device, you may wear it in addition to the NHS3-provided Fitbit.


What Fitbit model is provided in this study?

Fitbit Charge 5.



Can I use the Fitbit after the study is over?

You are free to use the Fitbit however you like after the study ends.



When will I need to wear the Fitbit?

You will need to wear the NHS3 Fitbit for 14 days, 24 hours a day (you may take it off to bathe or swim).



What if I have issues with wearing my Fitbit all day?

If you are not able to wear your Fitbit for the full 24 hours for a full 14 days (except for occasional charging, bathing, etc.), please contact study staff to let us know. If you cannot wear it because it is uncomfortable or you are having a skin reaction or irritation, please stop wearing the Fitbit and contact study staff at For advice on how to avoid any irritation, please see Fitbit’s Important Safety and Product and Services Information.



I work night and/or rotating shifts. How should I answer the sleep diary questions?

Please answer the questions regarding your longest sleep period. If you forget to fill out the sleep diary when you wake up, please complete it as soon as you remember. Please do not skip days. Instead, enter sleep information for the days you missed as best you can. If you do not sleep for a 24 hr period, please write “Did not sleep” at the top of the column for that day.


How do I return my sleep diary?

Please use the prepaid and pre-addressed envelope included in your NHS3 Sleep Kit to mail your completed sleep diary back to NHS3.




Is this study sponsored by Fitbit?

No, this study is not sponsored by Fitbit. We are using Fitbit devices to measure sleep, heart rate, and activity, but we are neither supported by nor partnering with Fitbit.




Can I look at all my sleep/exercise data during the study period?

You are free to interact with the Fitbit device and the Fitbit app during and after the study.




Should I change my sleep or physical activity during the study period?

No, there is no need to change your sleep or physical activity during the study period. The long-term goals of the research are to learn how various sleep schedules affect circadian rhythm in the general population.




What happens if I lose or break my Fitbit?

Please contact the study team at



I lost my instructions. Where can I get a new copy?

Please contact the study team at



When should I charge my Fitbit?

Because sleep is the focus of this research, we ask that you charge your Fitbit when you are NOT sleeping. You should charge your Fitbit fully before starting the study. Battery life is typically between 3-5 days, depending on usage and other factors, and a full charge will take 1-2 hours. Please keep your Fitbit charged, as a low battery will negatively affect data quality.




Should I start the study if I expect to travel in the next 14 days?

If you are going to travel (especially between time zones), we ask that you wait to begin the study until you complete your travel. If you have just returned from traveling between time zones, please wait until you have readjusted to your current time-zone to begin the study.




Will the Fitbit use my cellular data?

Syncing the Fitbit device to the Fitbit app will use a small amount of data.

For Fitbit Charge 5, approximately 50MB of data may be used over the 14-day study period.




How is my Fitbit data collected and stored?

Your Fitbit account data will be collected through Fitabase, a secure research platform. Your privacy is important to us. All Fitbit account data is encrypted while stored on the phone, awaiting upload, and in transit.




How can I ensure data collection is stopped after the 14-day study period?

Fitabase will automatically stop data collection from your Fitbit account after 28 days. At the end of the 14-day study period, you may elect to manually unlink your Fitbit account from Fitabase.