Income Levels Drive Migraine, Not Vice Versa

Pauline Anderson

August 30, 2013

Researchers have long wondered whether it's the socioeconomic environment, including household income levels, that influences the risk for migraine or whether having migraines limits achieving a higher economic status. Now researchers have confirmed that the former is the driving force.

"We've put that question to rest," said Walter F. Stewart, PhD, chief research and development officer, Sutter Health, Sacramento, California, who was lead author of a new study on the topic.

The study also showed that remission rates don't differ by household income levels.

"To me, the more interesting finding from the study is that whether or not you're in a higher or lower income group, the duration of time you have migraine doesn't vary," Dr. Stewart told Medscape Medical News.

The study is published online August 28 in Neurology.

Active Migraine

For this analysis, the researchers used data from the American Migraine Prevalence and Prevention study. A screening questionnaire was mailed to a random sample of 120,000 US households. Those with severe headaches completed a questionnaire that included age at first severe headache and the Migraine Disability Assessment (MIDAS) questionnaire, which included a question on the total number of headache days in the past 3 months.

Active migraine was defined as having at least 1 severe headache in the previous year and chronic migraine as having more than 15 severe headaches per month.

Dr. Walter F. Stewart

The sample was between ages 12 and 100 years.

Researchers categorized annual income of respondents into 3 groups for both males and females: under $22,500; $22,500 to 59,999; and $60,000 and over. According to Dr. Stewart, income is used as a surrogate for exposure to stress and other socioeconomic factors. The analysis did not include education as a confounder because it's strongly related to and represents the same socioeconomic domain as household income.

Using a statistical model that accounted for recall error, the researchers calculated migraine incidence and remission rates.

If the social selection theory — that having migraines leads to lower socioeconomic status (SES) — was at play, incidence and remission rates shouldn't vary by income categories. Conversely, if the social causation theory — that low SES causes migraines — was the driving force, those in the lowest income category would have higher incidence or lower remission rates than those who are more well off.

Of the 85,373 females in the analysis, 17.1% had current or active migraine and 27.3% were in the lowest income tertile. Of the 77,332 males, 5.6% had current migraine and 26.7% were in the lowest income tertile.

The researchers found that both females and males in the lowest income group were more likely to have extremely severe pain and grade IV MIDAS impact, less likely to have infrequent headache days (ie, 0 to 3 per month), and more likely to have used prescription medications in the past year.

Female and male age-specific migraine prevalence increased significantly as household income decreased (P < .01).The differences were not explained by race or other known confounders but largely by higher incidence rates at lower income levels.

Remission rates across all income groups for both males and females were not significant. "Lower income comes with a lot more stressors and not surprisingly, that translates into a greater chance of you getting a migraine, but the good news is that it will go away as fast as it would if you were in a high income group," said Dr. Stewart.

"It's almost as if there are 2 different kinds of processes — 1 getting migraines and another completely separate process that may be more related to genetic makeup that influences whether or not you will keep having them or whether you'll somehow adapt and stop having them."

Perhaps that second process somehow alters stress threshold levels, he added. "We all know intuitively that when we're exposed to stressors, we get better at managing them, so it may be that some adaptive response mediates that."

The study excluded chronic migraine because reverse causation (migraine raises risks for underemployment, which affects income) could introduce potentially significant confounding. As well, said Dr. Stewart, chronic migraine represents only a relatively small percentage of all migraine.

Although the study strongly supports the social causation hypothesis, the results don't exclude social selection as a possible explanation of some of the household income variance, said Dr. Stewart.

Caution Warranted

Authors of an accompanying editorial agreed that the study findings don't preclude a role for genetics and other endogenous factors.

This possibility may have implications for the design of future clinical trials and genetic studies, editorialists B. Lee Peterlin, DO, Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, and Ann I. Scher, PhD, Department of Preventive Medicine Biometrics, Uniformed Services University, Bethesda, Maryland, write.

"In fact, the authors speculate that pooling migraineurs with shorter and longer duration or including remitted migraineurs in control groups may have contributed to the negative findings in migraine genetic studies."

Some caution may be warranted in interpreting findings of the current study, Dr. Peterlin and Dr. Scher write. For example, the analysis used only 1 component of SES (income), which may not be fully representative of this multidimensional construct. "This may be particularly important given that education accounts for approximately two-thirds of the low SES score and approximately half of the high SES score in the SES index," they note.

The exclusion of chronic migraine is another consideration, as is the possibility that SES factors, such as race and marital status, may have contributed to the migraine-SES association "as this was not fully modeled," they said.

Migraine is heavily influenced by sex, with females being 3 times more likely than males to have these headaches. For both sexes, incident curves show that migraine rates tend to "take off" in the late teens and early 20s, a period of life fraught with stressors, such as leaving home and starting a career, said Dr. Stewart.

After peaking in the mid-20s, rates then fall off rapidly. "New starts after age 35 or 40 years are unusual compared to younger ages," said Dr. Stewart.

According to the study authors, the approach used in this research may apply to other chronic health problems with episodic manifestations, most of which are more common in lower income groups.

The study authors have disclosed no relevant financial relationships. Dr. Peterlin has received investigator-initiated research support from GSK and Luitpold Pharmaceuticals, receives royalties from Oxford University Press, and receives funding from the National Institutes of Health/National Institute of Neurological Disorders and Stroke and the Landenberger Foundation. Dr. Scher has received funding from the Center for Neuroscience and Regenerative Medicine, Defence Medical Research and Development Program, and Congressionally Directed Medical Research Programs.

Neurology. 2013;81:948-955, 942-943. Abstract  Editorial

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