OBJECTIVE To examine the effects of hypoglycemia on language processing in adults with and without type 1 diabetes.

RESEARCH DESIGN AND METHODS Forty adults were studied (20 with type 1 diabetes and 20 healthy volunteers) using a hyperinsulinemic glucose clamp to lower blood glucose to 2.5 mmol/L (45 mg/dL) (hypoglycemia) for 60 min, or to maintain blood glucose at 4.5 mmol/L (81 mg/dL) (euglycemia), on separate occasions. Language tests were applied to assess the effects of hypoglycemia on the relationship between working memory and language (reading span), grammatical decoding (self-paced reading), and grammatical encoding (subject-verb agreement).

RESULTS Hypoglycemia caused a significant deterioration in reading span (P < 0.001; η² = 0.37; Cohen d = 0.65) and a fall in correct responses (P = 0.005; η² = 0.19; Cohen d = 0.41). On the self-paced reading test, the reading time for the first sentence fragment increased during hypoglycemia (P = 0.039; η² = 0.11; Cohen d = 0.25). For the reading of the next fragment, hypoglycemia affected the healthy volunteer group more than the adults with type 1 diabetes (P = 0.03; η² = 0.12; Cohen d = 0.25). However, hypoglycemia did not significantly affect the number of errors in sentence comprehension or the time taken to answer questions. Hypoglycemia caused a deterioration of subject-verb agreement (correct responses: P = 0.011; η² = 0.159; Cohen d = 0.31).

CONCLUSIONS Hypoglycemia caused a significant deterioration in reading span and in the accuracy of subject-verb agreement, both of which are practical aspects of language involved in its everyday use. Language processing is therefore impaired during moderate hypoglycemia.