This video from the CDC explains the science behind a concussion and how the brain injury can affect athletes. (YouTube/CDC)

In recent years, warnings about the risks of concussions and football have come from retired players and active veterans, from coaches, medical and health-care professionals and from legions of lawyers. On Tuesday, one of the NFL’s brightest young stars added his name to the group.

San Francisco 49ers linebacker Chris Borland announced that at the age of 24, he will retire one year into a promising career, citing concern about the health risks associated with head injuries.

“I just honestly want to do what’s best for my health,” Borland told ESPN’s “Outside the Lines.” “From what I’ve researched and what I’ve experienced, I don’t think it’s worth the risk.”

Borland was the fourth NFL player age 30 or younger to retire in a week, and while none of the others tied his move to concern about head injury, the collective impact of their decisions served to unsettle the league and gave new life to an ongoing debate about football and safety, and the long-term viability of the game.

It’s clear that for the foreseeable future, at least, football will not suffer from a manpower shortage. For every player who makes the decision that Borland made, there are dozens of others who want to replace him. The NFL remains as popular as ever, and revenues are growing.

This video from the CDC illustrates and explains the science behind a concussion and the importance of recovery time for the human brain. (CDC via YouTube)

Still, Borland’s decision is significant, coming from a relatively high-profile player who has not yet made a fortune — in NFL terms — from the sport. If enough players and enough parents of prospective players reach the same conclusion that Borland reached, there will be consequences for football, even if they are felt far down the road.

“We are in the middle of the same discussion we had about smoking 40 years ago,” said Chris Nowinski, executive director of the Sports Legacy Institute, a nonprofit organization dedicated to addressing the sports concussion issue. “One side plays down the risks. One side tries to make sure the information is available so people can make properly informed decisions.”

Former Buffalo Bills defensive back Mark Kelso, who dealt with concussions as a player in the late 1980s and early ’90s and wore a helmet with padding on the outside of it to combat them, said that while he did not know Borland, his action pointed to the seriousness of the issue.

“It’s obvious that even with the improvement in helmet technology in recent years, the development of technology has not kept pace with what the issues are,” said Kelso, who is involved in developing safer helmets. “The game is going to suffer until we come up with adequate solutions.”

Borland’s decision comes after three other players — 49ers linebacker Patrick Willis, Pittsburgh Steelers linebacker Jason Worilds and Tennessee Titans quarterback Jake Locker — announced their early retirements last week. But none of those players cited fears about head injuries as Borland did.

Last year, Seattle Seahawks wide receiver Sidney Rice retired because of his increased awareness of the dangers of concussions. His interest intensified after he watched a documentary in which Dallas Cowboys Hall of Famer Tony Dorsett spoke of his daily battles with deteriorating health brought on by chronic traumatic encephalopathy, or CTE, a progressive degenerative disease of the brain linked to repetitive brain trauma.

In early March, Rice and New York Giants punter Steve Weatherford announced they would donate their brains to science research when they die. Rice estimated he has had eight concussions; Weatherford two.

This video from the CDC explains the signs and symptoms commonly experienced after one sustains a concussion. (YouTube/CDC)

Among the difficulties in dealing with head injuries is that symptoms manifest themselves in a variety of ways, and often not immediately. Changes in the brain brought on by CTE can begin many years after an athlete’s career is over. It’s also becoming increasingly clear that repetitive, small hits to the brain take their toll as well.

Michael Collins, director of the Sports Medicine Concussion Program at the University of Pittsburgh Medical Center, said he believes Borland’s announcement signalled that players and their parents are becoming overly fearful of concussions without being educated about medical advancements.

“My first feeling when I saw this was that I was really concerned about the misinformation that’s out there,” Collins said. “I feel [a] concussion is a fully manageable injury. . . . In the time I’ve been doing this, the pendulum has really swung. We weren’t taking it seriously enough in the 1990s. But now things have come all the way around to the other end. We need to make people aware of the advances we’ve made.”

Borland was third among NFL rookies last season with his 108 tackles. He was a third-round selection in last year’s NFL draft out of Wisconsin. Borland made just more than $1 million in bonus money and last season’s salary, and was to have a salary of $530,000 for the 2015 season.

“We respect Chris Borland’s decision and wish him all the best,” Jeff Miller, the NFL’s senior vice president of health and safety policy, said in a statement. “Playing any sport is a personal decision. By any measure, football has never been safer and we continue to make progress with rule changes, safer tackling techniques at all levels of football, and better equipment, protocols and medical care for players.”

Former Minnesota Vikings running back Robert Smith, who retired from the NFL at 28 after finishing second in the league in rushing in the 2000 season, said last week after the Willis, Worilds and Locker retirements that he wasn’t overly surprised. He said he expects more players will step away from the game early, not only because they have greater financial security but also because of greater awareness of the effects of head injuries.

“The money is such and the information is such that guys will do it,” Smith said. They’ll say that it’s far better to leave too soon than too late. There will be guys who don’t get to make that decision, who have that decision made for them for competitive reasons. And there will always be guys that stick around as long as they can because they love it so much and they can’t give it up. That won’t change.”