In recent years, much of the attention to brain problems in football players has focused on a condition known as CTE, which is traced to repeated head blows. The new study didn't look for CTE. It's not among the standard list of conditions the researchers used for classifying deaths, Lehman said.
But some of the brain disease deaths counted in the study may have actually come from misdiagnosed CTE, which stands for chronic traumatic encephalopathy, the researchers noted.
Dr. Robert Cantu, who co-directs a center that studies CTE at Boston University but did not participate in the new study, said the results are "not at all surprising." He agreed that some of the deaths could be misdiagnosed CTE, noting that the diagnosis requires a special chemical test of the brain after death.
Also on Wednesday, the NFL announced a donation of $30 million for medical research to the Foundation for the National Institutes of Health, the fundraising arm of the NIH.
NFL Commissioner Roger Goodell said the research could benefit athletes and potential areas of study may include CTE, concussion management and treatment and later in life disorders such as Alzheimer's.