New research ties pro football to a rare, fatal disease, and it raises real questions for parents of young athletes.

In 2024, former NFL running back Chris Johnson, who once held the league’s single-season rushing record, went public with an ALS diagnosis at age 40. He’s not alone. Over the past few years, a string of former players has come forward with the same disease, and it’s pushed scientists to ask a hard question. Does playing pro football raise a man’s risk of developing ALS? The other question we might also ask is how it is related to the other diagnosis we’ve seen in players, which is CTE (Chronic Traumatic Encephalopathy)? Early research suggests there’s a connection here, and the story behind that answer is worth understanding, whether you played the game yourself or you’re deciding whether your child should.

ALS, short for amyotrophic lateral sclerosis, is also known as Lou Gehrig’s disease, named for the New York Yankees’ first baseman who died from it in 1941. It’s a disease of the nerve cells that control voluntary muscle movement. Those cells slowly break down and die, and as they go, a person loses the ability to walk, talk, swallow, and eventually breathe. There’s no cure. Those cases have no known cause. Two medications, riluzole and edaravone, can modestly slow the disease, but they can’t stop it.

I once had a couple who came for a few sessions to help them work through the trauma of the husband having been diagnosed with ALS. His mother had died from the disease within six months of her diagnosis, and he wondered if that was how long he had to live. His greatest fear, as he described it, was that he would suffocate because the muscles that help us breathe would no longer function. I couldn’t imagine a worse disease to have at the end of your life. I assumed from what they were saying that he would not let that happen. He never returned for any sessions after his disclosure of his fear at that single session and he died a few months later.

Four Times as Likely

The largest study on ALS was conducted by Boston University’s CTE Center and Harvard Medical School’s Spaulding Rehabilitation Hospital and published in JAMA Network Open in December 2021. Researchers tracked every man who played at least one regular-season NFL game between 1960 and 2019, nearly 20,000 players in all. They found that these former players were about four times more likely to be diagnosed with ALS and four times more likely to die from it than men of the same age and race in the general public.

One detail stood out. Players who developed ALS had played in the league for an average of seven seasons, compared with about four and a half seasons for players who never got the disease. In plain language, the longer a man’s career, the higher his apparent risk. That pattern matters because it points away from a single bad hit and toward something that builds up over years on the field.

Scientists don’t yet know exactly why football seems to raise the risk of ALS. The leading idea involves repeated blows to the head, not just the concussions that cause dizziness and confusion, but the much more common sub-concussive hits that don’t cause obvious symptoms at all.

Genetics Plays a Role

A lineman can take hundreds of these small jolts in a single season. Researchers at Boston University have found that some of the same abnormal proteins that mark CTE, a separate brain disease tied to repeated head trauma, also show up in the spinal cords of men who had ALS. It’s still not clear why one disease shows up in some former players and the other shows up in others, or why some develop neither.

Fairness means considering the limits of this research, too. The number of NFL players who actually developed ALS in the BU study was small, just 38 men out of nearly 20,000, so the findings rest on a thin slice of cases. The study also can’t prove that football itself causes ALS. It shows a strong association, not a confirmed cause. Genetics plays a real role in some ALS cases, and scientists haven’t ruled out that something about the kind of man drawn to elite football, rather than the sport itself, contributes to the pattern. Earlier research comparing NFL players to retired Major League Baseball players found a similar elevated ALS risk only in the football group, which does point more toward the sport itself. However, the overall body of evidence is still developing.

What about kids? This is where the research turns directly toward parents. A Boston University study looked at the brains of 211 deceased football players with CTE and found that those who started tackle football before age 12 developed thinking and mood symptoms an average of 13 years earlier than those who started later. A separate BU analysis found that the risk of developing CTE roughly doubles for every two and a half years a person plays football, which is part of why the Concussion Legacy Foundation now advises parents to hold off on tackle football until age 14. The CDC has also reported that children in tackle football suffer head impacts far more often than those in flag football, with one comparison finding tackle players absorbed close to 400 impacts in a season versus single digits for flag players.

None of this means a child who plays football is destined for ALS. ALS, in particular, remains rare, and most of what’s known about it comes from men who played for many years at the professional level, a very different exposure from that of a child playing a few seasons of youth ball. But a young brain is still developing, and the evidence on repeated head impacts during those years is concerning enough that several physicians and researchers now recommend real caution.

A few practical steps for parents

Consider flag football or another non-contact version of the sport for children younger than 14. Several researchers and the Concussion Legacy Foundation have begun citing age as a reasonable cutoff, since it’s when full-contact tackling tends to begin producing the repeated head impacts linked to later problems.

If your child plays tackle football, ask the coaching staff what they’re doing to limit contact in practice, not just in games. Most of the head impacts a young player absorbs in a season happen during ordinary practice drills, not on game day.

Take every hit to the head seriously, even the ones that don’t look like a classic concussion. A child who seems a little foggy, irritable, or unusually tired after a hard practice deserves a break and a conversation with a physician, not a shrug.

Talk with your child’s physician about their individual risk factors, including any family history of neurological disease, before deciding which sport fits your family.

The science on football and ALS is still being written, and researchers are honest that they don’t have all the answers yet. What’s clear is that men who spent years absorbing hits at the professional level carry a measurably higher risk of this devastating disease, and that the years a child’s brain spends developing are not the years to treat head impacts casually. Whatever you decide about football in your own family, that decision deserves to be made with real research in hand, not just the tradition of the sport.