A home health care nurse is assessing a patient with type 1 diabetes who has been controlled for 6 months. The nurse is surprised and concerned about a blood glucose reading of 52 mg/dL. What action by this patient most likely caused this episode of hypoglycemia?

A. Using large amounts of sugar substitute in her tea this morning: Sugar substitutes contain noncaloric sweeteners and do not cause hypoglycemia. B. Taking a new form of birth control pill this morning: Oral contraceptives can affect glucose tolerance over time but are unlikely to cause an immediate hypoglycemic episode. C. Administering an insufficient dose of insulin this morning: Too little insulin would generally cause hyperglycemia, not hypoglycemia. D. A 2-hour long exercise class at the spa this morning: Prolonged exercise increases glucose uptake by muscles and insulin sensitivity, which commonly precipitates hypoglycemia in insulin-treated patients.