What's keeping you up at night? The answer may be the result of what you're doing before going to bed.
Researchers tracked 785 people's nightly routine for more than 5-thousand days.
Those who used nicotine, or drank alcohol, within four hours of going to bed were more likely to have interrupted sleep.
There was no impact on a person's sleep if they drank caffeine just hours before their bedtime.
However, the scientists say the amount of caffeine that was consumed was not measured, and how sensitive a person is to caffeine may also play a factor.