A study done in Sweden shows that people with four or more siblings were twice as likely to develop a brain tumor as people with no siblings. The correlation was only found with the number of younger siblings, not with the number of older siblings.

"Since the size of a family and the number of younger siblings correlate with the incidence of brain tumors, this suggests infectious agents may be causing the disease," said study author Andrea Altieri, DSc, with the German Cancer Research Center in Heidelberg, Germany. "The number of siblings a person has indicates they were exposed at an early age to infections, since children come in close contact with each other and thereby share exposures to many infectious agents."

According to Altieri, the finding that brain tumor rates were higher among people with younger siblings, and not older siblings, suggests infections or re-infections in late childhood may play an important role in causing the disease, while exposure to infections in infancy, birth to five months old, may be beneficial.

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"The two to fourfold increased risks for individuals with a high number of younger siblings are stronger than most established risk factors for the disease," said Altieri.

Tank goff my mom decided against having 8 kids.

Is that why my head hurts?