Marathoner died after using supplement called Jack3D with DMAA

The cause of death of a London Marathoner last April has been released by the coroner's office. Claire Squires collapsed near Buckingham Palace during the marathon, dying from heart failure.

The coroner's office announced that a dietary supplement the runner took may have contributed to the heart failure. According to the Associated Press, Squires' water bottle contained a scoop of Jack3D, a supplement containing dimethylamylamine, also known as DMAA.

While DMAA is on the World Anti-Doping Agency's banned list, the substance was purchased legally online. Even still, only elite runners would have been tested for drugs. According to Nicola Okey, spokeswoman for the London Marathon, "We just ask the rest of the runners to be medically fit. We don't make any other inquiries about what substances they are taking."

Okey also notes that following the findings, they will be amending the advice given to runners regarding the use of supplements.