A new study finds that people whose sleep is fragmented during the night are at higher risk of experiencing a migraine episode not the next day, but the day after that.

Dr. Suzanne Bertisch—a physician and clinical investigator in the Division of Sleep and Circadian Disorders at Brigham and Women's Hospital in Boston, MA—is the first and corresponding author of the new study, which now appears in the journal Neurology.

Dr. Bertisch and team started from the observation that sleep and migraine have been linked for a long time, both anecdotally and by scientific research.

For example, studies have found correlations between poor sleep quality and migraine, either with or without aura. Indeed, "disordered sleep, poor sleep quality, and insufficient or excessive sleep" are all known triggers of migraine and tension headaches.

Still, "When it comes to sleep and [migraine], there's a lot that we don't know," says Dr. Bertisch. "I became interested in this topic because [people with migraine] are frequently referred to me in the sleep clinic for help with treating their insomnia."

"Anyone treating these [people] wants to be able to counsel them on what to do to decrease their risk of [migraine], but the literature is unclear on what kind of sleep interventions may be helpful."

So, to zoom in on the nuances of this link between poor sleep and migraine, Dr. Bertisch and colleagues conducted a prospective cohort study of 98 adults. The study involved both diary recordings and objective actigraphy measures of sleep.

Studying sleep and migraine risk

The study participants experienced frequent migraine episodes, but on fewer than 15 days per month. They were 35 years old, on average.

For the study, the participants filled in electronic diaries twice per day, recording their "sleep, headaches, and other health habits" for a period of 6 weeks.

They also agreed to wear actigraphs on their wrists during this period. These devices can record sleep patterns in real time. Overall, the researchers used 4,406 days' worth of data.

During the study period, the participants experienced a total of 870 migraine episodes. After adjusting for other potential migraine triggers—including caffeine and alcohol intake, exercise, stress levels, and the day of the week—the researchers came to some interesting conclusions.

A 39% higher risk of migraine on 'day 1'

Sleeping for 6.5 hours or under each night, as well as having poor quality sleep, did not correlate with migraine episodes the next day or the day after that.

However, having fragmented sleep—as reflected both by diary entries and actigraphy measures—was linked with a higher risk of migraine on "day 1." This is not the day immediately following the night of fragmented sleep (day 0), but the day after that.

In fact, "Diary-reported low [sleep] efficiency was associated with a 39% higher odds of headache on day 1," the study authors report.

Dr. Bertisch and team conclude that "[s]leep fragmentation, defined by low sleep efficiency, was associated with higher odds of migraine on day 1."

"Sleep is multidimensional," says Dr. Bertisch, "and when we look at certain aspects [...], we found that low sleep efficiency, which is the amount of time you're awake in bed when you're trying to sleep, was associated with [migraine] not on the day immediately following, but on the day after that."

However, "Further research is needed to understand the clinical and neurobiologic implications of sleep fragmentation and risk of migraine," explain the study authors.