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What causes migraine headaches?

Experts are not certain what causes migraine headaches. In this video, Adel Olshansky, MD, a neurologist at West Hills Hospital, describes what might affect migraines, including vascular issues.
Dawn Marcus
Neurology
Like many health conditions, migraine is probably caused by a combination of genetic and environmental factors. Migraine tends to run in families, more often on the mother's side. Between half and two-thirds of people with migraine headaches have close relatives who also have them.

Studies of twins confirm that there is an important genetic component to migraines. A study of more than 8,000 adult twin pairs found that when one twin had migraines, an identical twin-who shares the same genetics-was over twice as likely to also have migraines, compared with a nonidentical twin, who has different genetics. This shows that about half the risk for migraine comes from your genes. The other half comes from environmental factors. In general, you have about a 50 percent chance of getting migraines if one of your parents has migraine, and a 75 percent chance if both parents have migraine. Even if neither parent has migraine, you might still develop migraine, in which case you may pass the condition on to your children.

Despite extensive study, researchers have still not discovered "the migraine gene." While some rare forms of migraine involve alterations or mutations in one or just a few genes, the common variety of migraine probably involves multiple genes. Abnormalities in several individual genes have been linked to an increased risk for migraine. Humans have 23 pairs of chromosomes, numbered 1 through 23. Chromosomes look like an "X" with short arms at the top and long arms at the bottom. The letter "p" in a chromosome's name refers to the short arms, and "q" refers to the long arms. Most studies have shown abnormalities on regions located on the short arms of chromosome 19 (or 19p) and the long arms of chromosome 1 (or1q). The strongest links have been shown for chromosome abnormalities in patients with familial hemiplegic migraine, a rare form of migraine that causes headache with prolonged weakness or paralysis of half of the body, in conjunction with the migraine.
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Experts aren't sure what causes a migraine headache and -- when it occurs -- an aura. For many years, scientists believed that a tightening of the cerebral arteries interfered with blood flow. The arteries would then dilate to compensate, not only in the brain but also outside the brain, where the dilation causes inflammation. Although scientists still believe that this combination of blood vessel dilation and inflammation causes migraine headache, they no longer think that the tightening of cerebral arteries underlies the aura.

Although researchers have confirmed that the aura coincides with a reduction in brain blood flow, this reduction isn't consistent with blood vessel constriction or spasm because these conditions would have a more substantial effect. Instead, many experts now suspect that the migraine aura is produced by a neurological phenomenon known as spreading depression, which is a wave of decreased electrical activity (indicating lower brain cell functioning) and diminished blood flow that inexplicably washes across the cerebral cortex. As neuronal communication is suppressed, cerebral blood flow diminishes. The areas of lowered activity gradually spread, as if washing across the brain, causing the symptoms of aura.
The exact cause of migraine is not fully understood. Most researchers think that migraine is due to abnormal changes in levels of substances that are naturally produced in the brain. When the levels of these substances increase, they can cause inflammation. This inflammation then causes blood vessels in the brain to swell and press on nearby nerves, causing pain.

Genes also have been linked to migraine. People who get migraines may have abnormal genes that control the functions of certain brain cells.

Experts do know that people with migraines react to a variety of factors and events, called triggers. These triggers can vary from person to person and don't always lead to migraine. A combination of triggers—not a single thing or event—is more likely to set off an attack. A person's response to triggers also can vary from migraine to migraine. Many women with migraine tend to have attacks triggered by:
  • Lack of or too much sleep
  • Skipped meals
  • Bright lights, loud noises, or strong odors
  • Hormone changes during the menstrual cycle
  • Stress and anxiety, or relaxation after stress
  • Weather changes
  • Alcohol (often red wine)
  • Caffeine (too much or withdrawal)
  • Foods that contain nitrates, such as hot dogs and lunch meats
  • Foods that contain MSG (monosodium glutamate), a flavor enhancer found in fast foods, broths, seasonings, and spices
  • Foods that contain tyramine, such as aged cheeses, soy products, fava beans, hard sausages, smoked fish, and chianti wine
  • Aspartame (NutraSweet® and equal®)
To pinpoint your migraine triggers, keep a headache diary. Each day you have a migraine headache, put that in your diary. Also write down the:
  • The time of day your headache started
  • Where you were and what you were doing when the migraine started
  • What you ate or drank 24 hours before the attack
  • Each day you have your period, not just the first day
This answer is based on source information from the National Women's Health Information.

The most common triggers that stimulate migraines are stress, weather changes, alcohol, changes in dietary or sleep patterns, and hormonal fluctuations, which cause "menstrual migraines" in some women. Other factors, such as caffeine, aged cheese, bright lights, exertion, smoke, and noise, are also triggers for some people. Triggers can be difficult to identify because it may be twenty-four to forty-eight hours between the trigger and the headache. Also, a particular factor may trigger a headache at some times but at other times may not. Many women have migraines when they are premenstrual but have them less often at other times.

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While researchers are not completely sure what causes a migraine headache, it’s believed to be the result of a complex cyclic contact between the cranial blood vessels and the trigeminal nerve.  A "trigger," such as food, stress, or fatigue, activates neurons that are in charge of releasing a selection of neuropeptides (substance P and neurokinin A). Substance P helps nervous system cells send messages to each other about painful stimuli. It is thought that when substance P levels are elevated in the body, they may produce higher levels of pain. The release of these chemicals causes an increase in blood flow to the brain. The distended blood vessels and the inflammatory response stimulate the trigeminal nerve to send out impulses back to the brain for processing, resulting in a migraine headache.
Michael T. Murray, ND
Naturopathic Medicine
Considerable evidence supports an association between migraine headaches and instability of blood vessels. The mechanism of migraine can be described as a three-stage process: (1) initiation, (2) prodrome (time between initiation and appearance of headache), and (3) headache. Although a particular trigger may be associated with the onset of a specific attack, it appears that initiation depends on an accumulation of several triggers over time. Once a critical point of susceptibility (or threshold) is reached, a "cascade event" is initiated, setting in process a domino effect that ultimately produces a headache. Food allergies, histamine-releasing foods, alcohol (especially red wine), stress, hormonal changes (e.g., menstruation, ovulation, birth control pills), and changes in weather (especially changes in barometric pressure) are some common triggers of migraines.
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The origin of migraine headaches is not completely understood; however, environmental factors and heredity seem to be a basis for the onset of these headaches. People with sensitive nervous systems are more likely to get migraine headaches. As a result, migraine headaches may also be caused by variations in the trigeminal nerve, a transporter of pain signals in the brain. A chemical imbalance in the nervous system may also cause migraine headaches. Brain chemicals, such as serotonin, help to keep nervous system pain in balance. If there is an imbalance, it could be causing your headaches.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.