In a large new US study, migraine headaches were found to be more likely to happen to people with lower household incomes, but tended to go into remission at the same rate for people at all income levels.
It was already well know that migraines were associated with lower income, said the new study's lead author Walter Stewart of Sutter Health in Concord, California. His first research suggesting the idea was published in 1992.
Since most people who get migraines eventually go into remission, he said, researchers wondered if remission was more common for people with higher incomes, which would have explained the connection between headaches and lower earnings.
Stewart and coauthors used data from 162,700 people with occasional, not chronic, migraines who were interviewed about their symptoms, including how old they were when the headaches began and the date of their most recent attack.
For both men and women, migraines became more common as income decreased.
And when participants were grouped by age, more women and men with migraines had household incomes under $60,000. For instance, among women ages 25 to 34, 37 per cent had household incomes under $22,500 (S$29,000), while 29 per cent fell between $22,500 and $59,999 and 20 per cent had household income greater than $60,000.
Previously, some had theorized that migraines cause people to function poorly at work and in life, gradually driving the headache sufferers from a higher to a lower income bracket, which is known as the "social selection" hypothesis explaining the income link.
Based on the current results, that is not a meaningful explanation, Stewart said.
He thinks social causation, in which stress or other factors related to lower income make someone more prone to migraines, is much more likely, he told Reuters Health.
"It has been hypothesized that a low socio-economic status is associated with more stressful life events (such as trauma, poor healthcare, ie. financial stress)," Dr. Barbara Lee Peterlin, director of headache research at Johns Hopkins Medicine in Baltimore, told Reuters by email.
"Stress has long been described as a trigger for migraine," both happy stresses, like marriage, and unhappy stresses, like combat, rape or car accidents, said Peterlin, who coauthored a commentary published with the new study in the journal Neurology.
The new results do the most so far to support the idea that low income, or something closely related to low income, causes migraines, according to Peterlin, but she believes migraines are "simply not simple," and that environment and genetics probably both play a role.
Stewart's group did not account for several factors that could influence the onset or remission of migraines, ranging from alcohol and tobacco use to access to healthcare.
According to 2009 survey data from the Centers for Disease Control and Prevention, 10 per cent of men and 23 per cent of women reported having had a migraine in the past three months.
Women are three times as likely as men to get migraines, which often begin to occur in the late teens and early adulthood, Stewart said. After sex and age, the most important predictor of migraines is income, he said.
Though Stewart believes his study nixed the theory that migraines cause changes in income, another study published in the same issue of the journal links the headaches, especially those accompanied by a so-called aura, to long-term changes in brain structure.
The review by Dr. Asma Bashir from the University of Copenhagen in Denmark and her colleagues examined 19 previous studies and determined that migraine sufferers were at increased risk for brain lesions, structural abnormalities and brain volume changes over time.
Once again, the researchers point out, more study is needed to determine what is cause and what is effect, and whether the lesions seen in the brains of migraine sufferers have any notable effects on brain function.