Mubeen Akhtar had been upset for the past few days as her fiancé Liaquat Ali had told her that their plans to marry were being opposed by some members of his family, said Muhammad Azim, a relative of the athlete.
Ali, himself a national athlete, was scheduled to represent Pakistan along with Akhtar at the London Olympics.
"Mubeen and Liaquat had a quarrel over the issue a couple of days ago. After that, she had not talked to anyone," Azim said.
After Akhtar took some poisonous pills today, she was rushed to Services Hospital, where she died. A doctor at the hospital said: "We washed her stomach but could not save her life."
Akhtar was recently declared Pakistan's fastest woman athlete. During the 44th National Athletics Championship, Akhtar clinched the women's 100-metre race after clocking 12.64 seconds.