"The decision came down to my health and my family," Joe Mauer wrote of his retirement in a letter posted online. (Jim Mone/AP Photo)

Joe Mauer announced his retirement Friday, writing that he was leaving baseball with a “full and grateful heart” after 15 seasons with the Minnesota Twins.

Mauer detailed his decision in a lengthy letter to fans, which the Twins posted online. The Twins are expected to hold a news conference Monday, according to MLB.com.

“The decision came down to my health and my family,” Mauer wrote in the letter. “The risk of concussion is always there, and I was reminded of that this season … The concussion I experienced [in the 2013] season not only changed my life professionally with a move to first base but changed me personally as well.”

Going through a concussion can be different for everyone, Mauer wrote, but his “personal experience” made him “look beyond baseball at what is best for me as a husband and father.”

“I am soon to be a father of three and I find myself thinking about my future health and its impact on my family more than I had years ago,” he wrote. “People always told me how much things change you become a parent, and they were right.”

Mauer — a six-time all-star and Minnesota native who spent his entire professional career with the Twins — thanked the team and its fans for making his career “as special and memorable as it was.”

“Because of you I can leave the game I love with a full and grateful heart,” he wrote.

Mauer, 35, won the American League MVP in 2009, when he was Minnesota’s catcher. He won three batting titles and three Gold Glove awards.

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