Abstract

Objective: Hypovitaminosis D and reduced insulin-like growth factor-1 (IGF-1) are associated, individually, with metabolic syndrome. Physiologic interactions between vitamin D and IGF-1 are reported; this is the first study to investigate their combined associations with metabolic syndrome prevalence.

Research Design and Methods: Data on 25-hydroxyvitamin D [25(OH)D], IGF-1, and metabolic syndrome abnormalities (abdominal obesity, raised HbA1c, blood pressure and triglycerides and low HDL-cholesterol) were collected from 6810 British whites in the 1958 cohort, surveyed 2002-2004 (age 45y).

Results: IGF-1 concentrations increased with 25(OH)D up to ∼75-85nmol/l, but not thereafter. Both 25(OH)D and IGF-1 were inversely associated with metabolic syndrome. There was an interaction between 25(OH)D and IGF-1 (p=0.025) on metabolic syndrome prevalence: IGF-1 was not significantly associated with metabolic syndrome among those with the lowest levels of 25(OH)D [p>0.09] whilst higher 25(OH)D was associated with metabolic syndrome at all IGF-1 concentrations (p≤0.006). Metabolic syndrome prevalence was lowest for participants with the highest concentrations of both 25(OH)D and IGF-1 [OR for highest vs. lowest third of both = 0.26 (0.17, 0.40), p<0.0001; adjusted for sex, month, hour, inactivity, alcohol consumption, smoking and social class]. 25(OH)D was associated with the prevalence of high HbA1c, blood pressure and triglycerides after adjustment for IGF-1, obesity and social and lifestyle variations (p≤0.004 for all comparisons).

Conclusions: Serum 25(OH)D is inversely associated with metabolic syndrome, while the inverse association with IGF-1 was found only among those without hypovitaminosis D. These results suggest that metabolic syndrome prevalence is the lowest when both 25(OH)D and IGF-1 are high.