If No Genetic Link, Family Income Affects Migraine Risk

NEW YORK, July 2 -- Showing evidence of a link between environmental factors and migraine, investigators here found that a higher family income may protect certain adolescents against migraine.

Children from families with an annual household income of ,000 or more had a 50% lower occurrence rate of migraine compared with children from households with an annual income less than ,500, researchers in a multicenter study reported in the July 3 issue of Neurology.

Yet the disparity was only in children who did not have family history of migraine. Income had no influence on migraine in families with a hereditary predisposition to the condition.

"This finding is consistent with the social causation but not the social selection hypothesis, because adolescents make a small contribution to household income," concluded the team led by Marcelo Bigal, M.D., of the Albert Einstein College of Medicine.

The results "mandate a search for environmental risk factors associated with low income which increase the one-year period prevalence of migraine," the researchers added. They plan to examine nutrition, emotional and physical stress, and disparities in treatment patterns as potential contributors to migraine.

Studies previously have shown that low-income adults have a higher prevalence of migraine. Two principal explanations have been offered for the observation:

• Social causation-factors associated with low income, such as stress, poor diet and limited access to medical care, conspire to increase the prevalence of migraine.
• Social selection-disease-related dysfunction interferes with educational and occupational functioning, which in turn lead to low income.

The link between income and migraine has not been examined carefully in young people, the current report noted. Dr. Bigal and colleagues sent a validated headache questionnaire to 120,000 U.S. households. Of 32,015 adolescents (ages 12 to 19) identified in the households, 18,714 (58%) returned the questionnaires.

The adolescents had a 6.3% overall prevalence of migraine. Girls had a higher prevalence (7.7%) than did boys (5.0%), and migraine was more common in whites than in African Americans.

The investigators separated the study population into income quintiles ranging from less than ,500 to ,000 or higher. They further stratified the data by family history. Among young people with a negative family history of migraine, income had a strong inverse association with prevalence, increasing from 2.9% in the highest income bracket to 5.5% in the lowest. Adjusted rates were 2.1% and 4.4%.

In contrast, migraine prevalence remained stable across the income strata in adolescents with a positive family history of migraine. The unadjusted prevalence was 12.1% to 12.3%, and the adjusted prevalence was 8.4% to 9.1%.

In an accompanying editorial, Andrew Hershey, M.D., Ph.D., a University of Cincinnati pediatric neurologist, commented that the "expression of migraine clearly involves a complex interaction of genetics and environment. Bigal et al . . . have clearly demonstrated that the interplay between socioeconomic status and genetics contributes to this complexity."

The authors noted several limitiations of the study. "The questionnaire was not specifically validated for adolescents," they wrote. "In those without a family history of migraine, where social causation is suggested, it may be that an unmeasured co-factor (e.g., depression, anxiety, substance abuse) may explain

this relationship."

They also looked at the severity and associated disability of the adolescents with migraine.

They found that "most adolescents have one to four migraine attacks per month, but 13.3% have more than four. During an attack, most (61%) are severely impaired or require bed rest. Most treat their usual attacks with over-the-counter drugs only, and just 16.5% consistently use prescription medications to treat their attacks."