25-hydroxyvitamin D, IGF-1, and metabolic syndrome at 45 years of age: a cross-sectional study in the 1958 British Birth Cohort.

OBJECTIVE: Hypovitaminosis D and reduced IGF-1 are associated, individually, with metabolic syndrome. Physiological 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 A1C, blood pressure, and triglycerides; and low HDL cholesterol) were collected from 6,810 British white subjects in the 1958 cohort, surveyed during 2002-2004 (age 45 years).
RESULTS: IGF-1 concentrations increased with 25(OH)D up to approximately 75-85 nmol/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), whereas 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 (odds ratio for highest vs. lowest third of both 0.26 [95% CI 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 A1C, 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, whereas 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.