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Two severe types of headaches are strongly linked to the body’s internal clock, a meta-analysis found.

Headaches and Your Internal Clock

The meta-analysis included 72 studies on how circadian rhythm—the body’s internal clock—appears to be involved in both cluster headaches and migraines, which together impact more than 40 million people in the United States.

Cluster headaches are a rare type of headache that cause bursts of intense pain around the eye. Each burst lasts about 15 minutes, but an attack can last between one and three hours. Cluster headaches commonly occur during the night.

Migraines usually come on during the day.

The studies included data on the time of day or time of year a person got a headache, and whether or not the headaches come on just before, during or just after sleep. Some of the studies also included research on whether certain genes associated with circadian rhythm are more common in people who get these types of headaches.

Cluster headaches were closely tied to circadian cycles, especially during season changes in the spring and fall, researchers found. More than 70 percent of people included in 16 studies on cluster headaches reported more attacks during these seasons and said they usually occurred between the late hours of the night and early hours of the morning.

The studies showed that five of the nine genes associated with cluster headaches were also involved in regulating circadian rhythms.

What surprised researchers was that half of migraine headaches across eight studies were associated with clear ebbs and flows throughout the day as well as the year. Most people had migraines during the morning, day or evening, and there was a stark drop off in the headaches from 1 pm to 7 am. They also reported more or worse migraines between April and October.

Many genes are associated with risk for migraines and the study found 110 of these genes were also tied to circadian rhythm.

The meta-analysis also found that people who get migraines often produce less melatonin than people who do not get headaches and produce even less during an attack. People with cluster headaches had both higher cortisol levels and lower melatonin levels.

The results were published in “Neurology” the American Academy of Neurology’s medical journal.

Cluster Headaches vs. Migraines

While there are similarities between both cluster headaches and migraines, there are certain distinctions:

1. Time: A cluster headache is brief, but it comes on fast and strong. The pain may vanish within 15 minutes to two hours. Migraines tend to build up slowly and last a long time. It can stick around for up to 72 hours.
2. How often: Cluster headaches tend to happen around the same time every day for weeks or months. During a cluster headache, you could have a headache every other day or up to eight in one day. Migraine pain may go up and down throughout the day. But it is rare to have more than one headache in a day.
3. Location: A cluster headache is unilateral. That means it only affects one side of your head. You may feel like it is right behind your eye or on the side of your forehead. You can have a migraine that is behind your eye, by your temple, on both sides, or in the front or back of your head.
4. How you feel: Cluster headaches often give you a sense of restlessness. You may feel better if you walk around. Your face or forehead may also start to sweat. Migraine headaches usually give you the urge to lie down and rest. In fact, the pain may get worse if you are active.

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