NFL commissioner Roger Goodell, in an email to 10 million names in its database Thursday, highlighted the league's safety programs and new emphasis on safety in youth football.

The letter came a day after two excerpts from a new book -- "League of Denial: The NFL, Concussions and the Battle for Truth" -- detailed what authors Mark Fainaru-Wada and Steve Fainaru claim was the NFL using its power and resources to downplay the effects of concussions on NFL players.

In his letter, Goodell said the NFL is committed "to deliver the game that the fans love and the safety that players deserve." He also wrote that "we will continue to find ways to protect players so they can enjoy longer careers on the field and healthier lives off the field."

The 1,000-plus-word letter comes on the heels of excerpts of "League of Denial," which ran on ESPN.com and in Sports Illustrated. The book claims that the NFL used its power and resources to discredit independent scientists and their work, that the league cited research data that minimized the dangers of concussions while emphasizing the league's flawed research and that league executives employed an aggressive public relations strategy designed to keep the public unaware of what league executives really knew about the effects of playing the game.