This year in the United States, an estimated 78,000 new cases of primary brain tumors will be diagnosed. The causes of brain and central nervous system tumors are largely unknown, but a new observational study has found a link between increased risk of developing a brain tumor and holding a university degree.
The researchers – from University College London in the United Kingdom and the Karolinska Institutet in Sweden – publish their findings in the Journal of Epidemiology & Community Health.
Meningiomas are the most common type of primary brain tumor, representing 36.4 percent of all primary brain tumors. Gliomas – a broad term including all tumors from the “gluey” or supportive tissue of the brain – account for 27 percent of all brain tumors and 80 percent of all malignant tumors.
Gliomas arise in glial cells that surround and support neurons in the brain.
The researchers of this latest study say few risk factors have been identified for brain tumors, but some include exposure to ionizing radiation and certain rare genetic syndromes.
To further investigate potential risk factors, the researchers used data on more than 4.3 million Swedes (resource no longer available at jech.bmj.com), who were born between 1911-1961 and who were living in Sweden in 1991.
All of the study subjects were monitored between 1993-2010 to see if they developed a primary brain tumor. In addition, the researchers gleaned data on educational attainment, disposable income, marital status, and occupation from national insurance, labor market, and national census data.
From 1993-2010, 1.1 million of them died and over 48,000 emigrated, but a total of 5,735 men and 7,101 women developed a brain tumor.
Results show that men with a university education that lasted at least 3 years were 19 percent more likely to develop a glioma, compared with men whose education did not go beyond compulsory schooling, which was 9 years of primary education. Likewise, women who went on to higher education had a 23 percent higher glioma risk and a 16 percent higher meningioma risk, compared with women who did not.
Furthermore, high disposable income levels were linked with a 14 percent increased risk of glioma among men. Interestingly, however, disposable income level was not linked with heightened risk of any brain tumor in women.
For both men and women, occupation played a role in risk. Men in professional or managerial roles had a 20 percent increased risk of glioma and a 50 percent increased risk of acoustic neuroma – a non-cancerous brain tumor that grows on the nerve affecting hearing and balance – compared with men in manual roles.
Women in professional and managerial roles had a 26 percent higher risk for glioma and a 14 percent higher risk for meningioma, compared with women in manual roles.
Another interesting finding from the study involved single versus married or co-habiting men. Single men had a lower risk of glioma but a higher risk of meningioma, compared with married or co-habiting men.
The researchers say they did not observe any of these associations among the women.
Although the study benefited from the large, population-based cohort, the researchers emphasize that this is an observational study, meaning that they cannot draw any conclusions about cause and effect.
Additionally, there were some study limitations. For example, the researchers did not have information on lifestyle factors that could influence the risk of brain tumor. It is also possible that the occupational results could be misclassified for those who changed their job after the information was recorded.
Still, the researchers say their findings were constant, which are a reflection of the strengths of using population data. They conclude:
”We observed consistent associations between higher SEP [socioeconomic position] and higher risk of glioma. Completeness of cancer registration and detection bias are potential explanations for the findings.”