But then a specialised clinic opened in the Iztapalapa district of Mexico City, and everything changed.
He began attending the clinic regularly, drawn by the convenience of having many diabetes needs covered under one roof. The clinic has a strong focus on diet and exercise, educating patients and their families about how to take care of themselves.
"They are tough on me," he says with a smile, adding: "It has become a way of life, a sense of belonging."
Today, with the support of his wife and the Iztapalapa Diabetes clinic, his diabetes is under control.
Mr Castro's care was offered through WDF15-1228