The birth mother of San Francisco 49ers quarterback Colin Kaepernick has spent years trying unsuccessfully to connect with the son she gave up for adoption when he was an infant, Yahoo Sports reported.

Heidi Russo, a 44-year-old registered nurse who now lives in a Denver suburb, was a 19-year-old single mother in Milwaukee when her six-week old son was adopted by Rick and Teresa Kaepernick. She told Yahoo Sports that although she knows being raised by the Kaepernicks was the best thing for Colin, there were many times she wished she could get Colin back.

She has contacted the Kaepernicks as well as Colin over the years, and even went to see him play a game while he was at the University of Nevada. Russo's preferred method of reaching out to Colin has been through Twitter, where they've exchanged some messages.

However, Kaepernick who has made no secret of his devotion to his adoptive family, has thus far not been interested in meeting in person with Russo.

"I watch him now and I see how happy he is and I'm thrilled for him," Russo told Yahoo Sports' Jason Cole. "I have to respect" his decision not to meet.

Virgil Green, a Denver Broncos tight end and Kaepernick's former teammate and roommate at Nevada, told Yahoo Sports that Kaepernick has strong feelings for resisting overtures from his birth mother.

":I think he would view it as almost treasonous to them to meet with his biological mother or father," Green said. " They did such a great job giving him everything he needed to be successful in life."

Rick and Teresa Kaepernick have said they have always supported any decision Colin makes in terms of his interaction with his birth parents. Russo said the couple used to send her letters as well as pictures of Colin until he was 6 or 7, then the correspondence stopped.

Russo, who has an 8-year-old son, attended a 49ers preseason game in Denver on Aug. 26 with her son. While she hoped to meet Colin afterward, Russo did meet up with Rick and Teresa Kaepernick for the first time in decades.

"It was like meeting old friends after 25 years," Russo told Yahoo. "You couldn't ask for better people than Rick and Teresa, how they have loved him and taken care of him. As a parent, you never think that anyone could love your child as much as you do, but they have.

"You can see that everything he wants and everything he has worked for is coming together," she said. "That's something that any parent would be happy to see for their child."