SAN FRANCISCO — Despite a significant increase in reported concussions in 2015, the NFL’s chief medical adviser and a member of the league’s Head, Neck and Spine Committee said Thursday there are promising developments that leave them encouraged about improving players’ health.

“I’m a firm believer in the power of research and how discovery and innovation can make advances to improve health,” Dr. Betsy Nabel, the chief medical adviser, said at a news conference. “The NFL has a real opportunity to continue to invest in the best research and to make advances to improve player health and safety.”

The league announced last week that 271 concussions were documented in 2015, an increase of 65 from 2014 and the highest number since 2012, when 261 were reported. One reason for the increase, according to Jeff Miller, senior vice president of health and safety policy, was that the league’s reporting policy expanded beyond simply players missing games.

Even so, league officials were concerned enough about the increase to continue the emphasis on research to prevent and treat concussions.

“In the past 30 years, I’ve seen a tremendous effort, especially in the last decade, with our understanding of neuroscience,” Dr. Mitch Berger, a California-based neurosurgeon on the Head, Neck and Spine Committee. “This has been something near and dear to my heart.”

But not everyone is convinced the NFL’s intentions are pure. Former Harvard football player Chris Nowinski, the founding executive director of the Boston-based Concussion Legacy Foundation, said the league continues to drag its feet on important issues affecting current and former players.

“I do not believe the NFL is engaged in a good-faith effort,” said Nowinski, who attended the news conference.

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Nowinski has drawn attention to research on chronic traumatic encephalopathy (CTE), a degenerative neurological disease that has been diagnosed in more than 100 former NFL players who donated their brains to research following their deaths. It was reported this week that former Raiders quarterback Ken Stabler, who died last July, was diagnosed with the disease after an autopsy.

Nowinski was particularly troubled by the NFL’s resistance to a study commissioned by the National Institutes of Health to diagnose CTE in living people. Nowinski said the league had issues with a researcher from Boston University who was involved in the study.

“Their attempt to prevent that study from being funded is frankly a slap in the face to every family suffering from CTE right now,” Nowinski said. “It’s a lot of games [being played], and those games hurt a lot of people. The frustrating part is that I sort of feel I’m reliving big tobacco in real time.”

Berger said it is too soon to draw a direct link to brain trauma suffered by NFL players and CTE.

“At some point, if we’re going to find a link in football, we also have to find a link in the military population, in the civilian population, to put this story together,” Berger said. “We have to move forward over time. We have to assess our players as time goes on.”

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Berger said there is “no question you can find degenerative changes that are indicative of CTE in individuals who have played football. [But] we’ve seen it in young people who have had autopsy for other reasons not related to brain trauma. We’ve seen evidence of a number of players who have come to autopsy who have had the [CTE] diagnosis. We have also seen a number of former players who do very well. I played football in college and I had three concussions. I don’t have any problems. I may have tau [a protein found in post-mortem brains with CTE] deposition, but I’m doing pretty well.”