Hypoglycaemic valleys: an under-recognised problem in type 2 diabetes?

In the treatment of type 2 diabetes, mild (self-treated) hypoglycaemia is associated with some oral hypoglycaemic agents and with insulin, but is perceived to be uncommon; severe hypoglycaemia (requiring external help) is thought to be rare. Ageing per se modifies the counterregulatory (CR) hormonal and symptomatic responses to hypoglycaemia and alters the glycaemic thresholds at which these occur. In type 2 diabetes, subtle CR hormonal deficiencies occur, and the glycaemic thresholds are set at higher blood glucose levels compared with non-diabetic subjects or people with type 1 diabetes. When significant insulin deficiency occurs, CR hormonal deficiencies appear, and glycaemic thresholds are modified when glycaemic control is improved with insulin therapy. Although symptomatic hypoglycaemia is reported to be uncommon in sulphonylurea-treated type 2 diabetes, its frequency may be underestimated; severe hypoglycaemia is rare. In insulin-treated type 2 diabetes accurate data of the frequency of hypoglycaemia are difficult to obtain, but an annual prevalence of 30 to 40% has been recorded for mild hypoglycaemia in clinical trials and 0.5 to 2.3% for severe hypoglycaemia. The true overall frequencies may be much higher, and rise with increasing duration of insulin therapy, duration of diabetes, and age. Patients with type 2 diabetes with progressive pancreatic beta cell failure increasingly resemble those with type 1 diabetes. The syndrome of counterregulatory hormonal deficiency may develop, but impaired awareness of hypoglycaemia is uncommon.