Gut Check looks at health claims made by studies, newsmakers, or conventional wisdom. We ask: Should you believe this?
The Claim: Going to college or being married is associated with a higher risk of brain cancer, found a study published on Monday in the Journal of Epidemiological and Community Health.
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Using a huge registry of health and other data on all Swedes, European researchers found that people with at least three years of college had about a 20 percent higher risk of glioma (the most common brain tumor) as those with only an elementary-school education. And married men had a 23 percent higher risk of glioma than never-married men.
The absolute risk of these rare tumors, however, was still small. By 2010, the end of the 17-year tracking period, 12,836 people (0.3 percent) had been diagnosed with brain tumors — gliomas, meningiomas, and acoustic neuromas, which have been linked to cellphone use. All this works out to 18 people rather than 15 out of 10,000 developing glioma. (The researchers did not look specifically at the deadliest form of brain cancer, glioblastoma, which kills half of patients in little over a year.)
But the results are messy. Education was not associated with acoustic neuroma. And marriage was linked to a higher risk of glioma only in men, not women, and to a lower risk for men of the even rarer meningioma.
Neither the authors, led by epidemiologist Maria Feychting of Sweden’s Karolinska Institute, nor outside experts think being married or educated causes brain cancer. “From a biological standpoint, I don’t know why educational or demographic factors factors would change your risk of glioma,” said Jill Barnholtz-Sloan of Case Comprehensive Cancer Center, who led a 2014 review of risk factors for gliomas. Those include half a dozen genetic variants, rare inherited disorders such as neurofibromatosis, and ionizing radiation such as that from X-rays.
So what’s going on?
The study is statistically sound, experts told STAT, with data from 4.3 million people who were 32 to 82 when the researchers began to track them in 1993.
Also making the new research credible: a “cohort” study like this, following people from one point in time, is more rigorous than comparing two groups of people (with and without brain tumors) at a single point in time. And using a national registry like that in Sweden, which has universal health care, means you’re not missing people who don’t see doctors — and get diagnosed — due to a lack of insurance.
A hint to what’s going on comes from a 2002 US study. It found that both higher-income and married people had a higher risk of glioma and some other brain cancers. But that was true only for “low-grade,” slower-growing kinds, suggesting that “differences in the completeness or timing of diagnosis may have played a role,” those authors wrote.
That is, affluent and/or educated people might be more attuned to the subtle symptoms of low-grade brain tumors, such as changes in personality, mobility, or speech. For some of the tumors that the Swedish study found to be more common in the educated and the married, “you can have it for a long time, and even die with it — but not from it,” said epidemiologist Elizabeth Ward of the American Cancer Society. “Even though everyone in Sweden has access to medical care, there are differences in knowledge and awareness and the ability to take time off from work. I think it’s a plausible explanation” that educated people with symptoms would see a doctor sooner than less educated, less affluent people, she said.
Only people whose brain cancer is officially diagnosed get counted in the registry, of course, and therefore in studies like this one. The less educated might have the same number of gliomas, but simply not be catching them — and therefore dying of something else before they’re diagnosed. That could account for the more/less educated differences.
Something similar could explain the elevated risk of glioma and meningioma among married men (but not women). A spouse’s up-close view of his or her partner makes it more likely that gliomas in married people would be noticed sooner and lead to a doctor visit and earlier diagnosis. “Men, who in general are less likely than women to seek health care, might be having symptoms but ignoring them,” said Karla Ballman, chief of biostatistics at Memorial Sloan Kettering Cancer Center. “But if they’re married, their wife tells them to go to the doctor.” As for why husbands don’t tell their wives to, readers are invited to supply their favorite cliche about oblivious males.
Being married or educated seems linked to being diagnosed with some kinds of brain tumor, likely because of socioeconomic rather than biological differences — a useful reminder that when studies count diagnoses they’re not necessarily counting every case.