Even a single season of high school football might have harmful impacts on the brain

At this point, it's well-known that years of playing football can cause long-term mental problems. It's also strongly suspected that this is true for players who merely suffer routine blows to the head — and are never even diagnosed with a concussion.

Brain damage might occur even more quickly than many feared

But new research, presented yesterday by Wake Forest scientists at the annual meeting of the Radiological Society of North America, suggests that the damage can occur even more quickly than many people feared.

Their analysis of 24 high- school football players found a correlation between the number of hits each player took in a season and changes in the corpus callosum and other areas of the brain known to be affected by concussions.

Now, the researchers didn't link these changes in the brain to actual behavioral changes, and they don't know for sure they were caused by football — they found a correlation, not a causation. Still, it's a disturbing finding given the mounting pile of evidence that football causes brain damage on a scale much larger than we realized.

What the researchers found

A high school game in Virginia. (John McDonnell/The Washington Post via Getty Images)

The researchers worked with something called the Kinematics of Impact Data Set (KIDS). In essence, it involves putting accelerometers in football helmets that measure the frequency and severity of hits, then letting youth players wear the helmets over the course of a season or more.

The researchers used this data for 24 high-school players between the ages of 16 and 18. These players also underwent diffusion MRI scans before and after the season, which allows doctors to see how fluids move through the neurons in their brains' white matter, potentially revealing any abnormalities in the tissue.

the "heavy hitters" showed higher levels of changes in their brains

Using the accelerometer data, the researchers split the players into two groups: 9 of them were so-called "heavy hitters," who took many blows to the head, and 15 were "light hitters," and took fewer. None were diagnosed with a concussion during the season.

All of these players showed changes in their brains' white matter that the researchers called "concerning" — and the heavy hitters showed significantly higher levels of these changes than the light ones. The changes were disproportionately found in the corpus callosum and other areas deep in the white matter (which lies below the grey matter at the outer surface of the brain), which previous research has found to be frequently affected by concussions.

Again, as far as we know, the players didn't demonstrate any symptoms during the season and the researchers didn't establish any link with actual brain problems. They see this as an initial step in researching the effects of football on young brains. But seen in the light of other things we've recently learned about head trauma, these findings are rather concerning.

What we know about football and the brain

Ann McKee, one of the leading neurologists looking into CTE, examines a brain at Boston University's brain bank. (Stan Grossfeld/The Boston Globe via Getty Images)

Over the past decade or so, several prominent former NFL players have committed suicide after suffering from years of emotional and memory problems. When doctors examined their brains afterward, they found evidence of a long-term disease called chronic traumatic encephalopathy, or CTE.

For nearly a century, doctors knew the disease could occur in boxers who were repeatedly punched in the head (they called it "punch drunk"), but awareness that football players were also susceptible came slowly. In 2002, Mike Webster — a former Pittsburgh Steelers player who suffered from depression and dementia before dying from a heart attack at age 50 — was diagnosed, becoming the first former NFL player confirmed to have it.

Although the symptoms may appear during a patient’s lifetime, a definitive diagnosis can only be made after death, when doctors have the chance to examine the brain and look for telltale signs of the disease. In postmortem exams, heavy depositions of a protein called tau in the brain are one sign of CTE.

Left: a normal brain (slice at top, microscope slide at bottom). Right: a brain with high amounts of tau. Boston University

At least 50 retired NFL players have been diagnosed with CTE so far, but hundreds more are probably living with it undiagnosed. Scientists have found it can cause a range of problems — headaches, difficulty concentrating, erectile dysfunction, depression, increased anger and aggression, reduced impulse control, and eventually, severe dementia — which often don't appear until years after a player has retired.

Most players diagnosed with CTE played for many years and suffered multiple concussions, but that's not always the case: in 2010, a 21 ­year-­old University of Pennsylvania football player named Owen Thomas killed himself and was found to have early stages of CTE, making him the one of the youngest cases diagnosed so far.

in 2010, a 21 year-old college football player killed himself and was found to have cte

The most recent, most disturbing finding about CTE is the mounting evidence that mild, routine hits — which present no immediate symptoms and are generally categorized as sub-­concussions, rather than concussions — might also lead to CTE. Last spring, new research came out showing that, like these high school players, college football players have detectable changes in their brains after spending just a few years on the field, and heavier hitters have more pronounced changes.

What's more, research suggests that efforts (at both the pro and college level) to more rigorously screen for concussions and keep concussed players out of the game are still far from perfect. One study found that more than 80 percent of concussions at the college level still go unreported.

Scientists still don’t really understand how repetitive brain trauma causes CTE. Some hypothesize that milder hits contribute to it by disrupting the blood-­brain barrier (the lining that prevents molecules in your bloodstream from entering your brain), potentially causing undetectable long-­term damage.

This could be a big problem because a lot of football players experience these sorts of hits over and over throughout a game as a matter of routine. Getting rid of vicious hits and severe concussions is one thing, but eliminating these routine hits might just not be possible. If CTE is as common as some scientists believe, the NFL could have an epidemic on its hands.

Watch: Can the NFL survive its concussion crisis?

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