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Hypovitaminosis D is associated with insulin resistance and beta cell dysfunction
Ken C Chiu1, Audrey Chu, Vay Liang W Go
1Division of Clinical Epidemiology and Preventive Medicine, Department of Medicine, University of California-Los Angeles School of Medicine, 924 Westwood Boulevard, Los Angeles, CA 90024, USA. kchiu@mednet.ucla.edu
Background:
Although the role of vitamin D in type 2 diabetes is well recognized, its relation to glucose metabolism is not well studied.
Objective:
We investigated the relation of 25-hydroxyvitamin D [25(OH)D] concentrations to insulin sensitivity and beta cell function.
Design:
We enrolled 126 healthy, glucose-tolerant subjects living in California. Insulin sensitivity index (ISI) and first- and second-phase insulin responses (1stIR and 2ndIR) were assessed by using a hyperglycemic clamp.
Results:
Univariate regression analyses showed that 25(OH)D concentration was positively correlated with ISI (P < 0.0001) and negatively correlated with 1stIR (P = 0.0045) and 2ndIR (P < 0.0001). Multiple regression analyses confirmed an independent correlation between 25(OH)D concentration and ISI (P = 0.0007). No independent correlation was observed between 25(OH)D concentration and 1stIR or 2ndIR. However, an independent negative relation of 25(OH)D concentration with plasma glucose concentration was observed at fasting (P = 0.0258), 60 min (P = 0.0011), 90 min (P = 0.0011), and 120 min (P = 0.0007) during the oral-glucose-tolerance test. Subjects with hypovitaminosis D (<20 ng/mL) had a greater prevalence of components of metabolic syndrome than did subjects without hypovitaminosis D (30% compared with 11%; P = 0.0076).
Conclusions:
The data show a positive correlation of 25(OH)D concentration with insulin sensitivity and a negative effect of hypovitaminosis D on beta cell function. Subjects with hypovitaminosis D are at higher risk of insulin resistance and the metabolic syndrome. Further studies are required to explore the underlying mechanisms.