The doctor explained that cortisol boosts your blood sugar levels by converting protein into glucose.
With singing you might be able to see instant results, the doctor wrote.
Dr Mosley added: “I remember, some years ago, seeing a middle-aged patient who was in the hospital for an operation, but her blood pressure was so high that the surgeons were anxious about operating.
“She began singing quietly to herself, and within 20 minutes her blood pressure had fallen enough for the operation to proceed.”