When senior U.S. Senator Richard Blumenthal wrote of NHL Commissioner Gary Bettman's "ongoing indifference and disregard" for scientific evidence linking chronic traumatic encephalopathy, or CTE, to repetitive hits to the head (whether concussive or subconcussive), he was being polite.

When Sen. Blumenthal wrote that the NHL "would prefer that athletes remain ignorant of potentially very serious threats to their health," he was right.

Just as he, the ranking member of the Senate's Consumer Protection subcommittee, was right when he concluded the following:

"Most puzzling is why you attack others for asking these profoundly important questions. Instead of aggressively seeking to advance the science surrounding concussions, you accuse the ‘media’, ‘media consultants’, lawyers and players of ‘fear mongering’. Your letter suggests that seeking facts about concussions and CTE could instill ‘unwarranted fears’ that lead to ‘depression’ and 'suicide.' Your leadership guides professional players who are admired and revered by junior, college, amateur and youth hockey players. Your failure to take a safety issue seriously could have ramifications for players at every level, seriously affecting public health…The NHL has a duty to behave responsibly in light of its public trust."

In recent weeks, Bettman has doubled down with a 24-page letter denying any link between CTE and the repetitive blows to the head that come with playing in the NHL.

In it, he drew on a few main arguments. First, the commissioner argued that research has concluded that CTE cannot yet be diagnosed in living patients. Second, he plucked cautious phrasing from the Boston University's CTE Center and the National Institutes of Health's research -- which has largely found irrefutable overwhelming evidence of CTE in athletes in contact sports such as boxing and football -- to suggest that research is in its "infancy" and thus not absolute.

But despite the current inability to diagnose CTE in living patients, we have years of scientific study, evidence and opinion has still led experts to the same conclusions. Nearly 90 years of scientific conclusions on contact to the head and CTE suggest that even though research into the disease isn't complete, there are certain things we know.

Gary Bettman wants us to believe that what experts know about head trauma, concussions, repetitive blows to the head, and CTE isn't sufficient to prove a link. But they know a lot. Here's what they've found:

At least six former NHL players (Derek Boogaard, Reg Fleming, Bob Probert, Rick Martin, Steve Montador and Larry Zeidel) have been diagnosed with CTE post-mortem.

The United States' Third Circuit Court ruled that there is a link between playing football and developing CTE. In March, the NFL plainly admitted (after years of denial) the link, telling a congressional committee that "The answer to that question is certainly yes," which the Third Circuit Court called "conceding something already known."

The CTE Center at Boston University has, for years now, said that they "believe CTE is caused by repetitive head trauma." They further describe CTE as "a progressive degenerative disease of the brain found in athletes (and others) with a history of repetitive brain trauma, including symptomatic concussions as well as asymptomatic subconcussive hits to the head."

The Psychiatry Neuroimaging Laboratory at Harvard Medical School agrees:

"CTE is thought to result from repetitive brain trauma … CTE has been observed most often in professional athletes who are involved in contact sports."

Michael Strong, the dean of Western’s Schulich School of Medicine and Dentistry, emphasized that denial of a link stems from ignorance.

"You don’t ever hear anybody at the other end of the pipeline saying, ‘we don’t really think stroke is related to hypertension because nobody has ever proved it,’" he said. "Here, we’ve got somebody (Bettman) at the other end of the pipeline saying, ‘well we don’t really think there’s a relationship between CTE and concussion and playing sports.’ It makes no sense to say something like that."

Bennet Omalu, the doctor who first found CTE in NFL players, states unequivocally that "CTE is a progressive degenerative disease that afflicts the brain of people who have suffered repeated concussions and traumatic brain injuries." When Omalu finished his third study into CTE in NFL players, he concluded that he was "absolutely not" surprised that CTE was evidenced in all three studies.

The Mayo Clinic calls CTE "brain degeneration likely caused by repeated head traumas."

American Academy of Neurology meeting found that 40 per cent of retired NFL players showed sings of traumatic brain injury based on scans.

A 2016 Jama Neurology study "associated" CTE with repetitive head trauma.

CTE was first described in 1928 as characteristic of boxers "who take considerable head punishment."

A study conducted by Brandon Gavett, Robert Stern and Ann McKee posits in its first sentence that "it has been understood for decades that certain sporting activities may increase an athlete's risk of developing a neurodegenerative disease later in life."

They found that "CTE has recently been found to occur after other causes of repeated head trauma, suggesting that any repeated blows to the head, such as those that occur in American football, hockey, soccer, professional wrestling, and physical abuse, can also lead to neurodegenerative changes."

In Brain Imaging and Behaviour's paper, "Chronic traumatic encephalopathy: neurodegeneration following repetitive concussive and subconcussive brain trauma," concludes that CTE affects, in particular, "contact sport athletes and those with a history of military combat" and that "repetitive brain trauma" is the only established risk factor for CTE.

Another Robert Stern and Ann McKee study, alongside CTE researchers and experts Robert Cantu and Christopher Nowinski, links "participation in contact sports" to CTE.

Their study, titled "Long-term Consequences of Repetitive Brain Trauma: Chronic Traumic Encephalopathy," concludes that "Given the millions of youth, high school, collegiate, and professional athletes participating in contact sports that involve repetitive brain trauma, as well as military personnel exposed to repeated brain trauma from blast and other injuries in the military, CTE represents an important public health issue."

And that's just the tip of an iceberg of growing scientific evidence and opinion on the topic. Just as the NFL was forced into conceding the link between CTE and contact to the head, so too will the NHL have to someday. Until then, Bettman's voiced ignorance impacts the decisions of both healthy and concussed hockey players and their parents. None of his commentary should be taken seriously, and all future coverage of his stances on science in hockey (regarding CTE or otherwise) should be matched against evidence and experts.