Desiree Linden is a Boston Marathon winner used to a heavy training regimen. Suddenly in 2017, her energy and motivation evaporated. Inexplicably, her hair started to fall out and she gained weight. The diagnosis? Hypothyroidism, a condition that left untreated, could cause coma and even death. In this excerpt from her book, “Choosing to Run” at Runner’s World, Linden recounts chafing at being urged to take a synthetic hormone to save her life.

Getting in shape after the broken femur was straightforward, if tedious. It was a matter of putting in time and seeing the logical return on that investment. By comparison, up against something systemic and invisible such as thyroid levels, I faced a new mini-mystery every day. I didn’t know when and how I’d get knocked down. I wasn’t sure about my next steps as I tried to piece together a workout and race schedule that would get me ready to run respectably in Boston. I looked for shorter races where there would be few to no expectations freighted on me.