Insulin-like growth factor-1 and cognition in normoglycemia, prediabetes, and type 2 diabetes mellitus

Background: The relationship between insulin-like growth factor-1 (IGF-1) and cognition has been studied in healthy individuals, but not extensively with regards to insulin resistance and type 2 diabetes mellitus (T2DM). In this retrospective observational study, we investigated relationships of IGF-1 with memory and executive function across people with normoglycemia, prediabetes, and T2DM. Methods: Data from the Midlife in the United States (MIDUS) study were used. Episodic memory and executive function were assessed using the Brief Test of Adult Cognition by Telephone approximately 21.42 +/- 12.10 months prior to measuring IGF-1 levels from a fasting blood sample. Normoglycemia was identified as individuals without a physician diagnosis of diabetes and glycated hemoglobin (HbA1c) <= 5.6%. Prediabetes was identified as those without a physician diagnosis of diabetes and HbA1c between 5.7%-6.4%. T2DM was identified as anyone with a physician diagnosis of diabetes, or HbA1c >= 6.5%, or anyone using an oral hypoglycemic medication. The associations were assessed using linear regressions controlling for age, sex, education, body mass index, C-reactive protein, HbA1c or homeostatic model of insulin resistance, MIDUS wave, exercise, smoking status, sleep quality, alcohol intake, oral hypoglycemic use, and insulin use. Results: The study included 1400 participants, which consisted of 583 normoglycemic (48.4% female, mean age 51.0 +/- 12.2 years), 512 prediabetes (58.4% female, mean age 57.3 +/- 11.8 years), and 305 T2DM participants (53.8% female, mean age 57.6 +/- 11.5 years). Peripheral IGF-1 concentrations were lower (F-2,F-1397 = 28.29, p < 0.001) in people with prediabetes or T2DM, vs. normoglycemia. Participants with prediabetes or T2DM had lower episodic memory (F-2,F-1397 = 9.21, p < 0.001) and executive function (F-2,F-1397 = 20.29, p < 0.001) composite z-scores than people with normoglycemia. Higher IGF-1 concentrations were associated with better executive performance in individuals with prediabetes (beta = 0.115 [0.028, 0.202], p = 0.010), but not in individuals with normoglycemia or T2DM. An interaction between IGF-1 and sex in predicting executive function was observed in the prediabetes group (beta = -0.344, p = 0.042), where the relationship was weaker in females (beta = 0.106 [-0.012, 0.224], p = 0.077) than males (beta = 0.251 [0.123, 0.380], p < 0.001). No associations were seen between IGF-1 and memory. Conclusion: The results suggest that peripheral IGF-1 concentrations may be related to executive function, and that the relationship may be sex-specific and dependent on diabetes status.