The role of insulin-like growth factor I components in the regulation of vitamin D.

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

• Level A · Stronger Clinical Evidence
• Level B · Emerging clinical evidence with positive signals
• Level C · Early human research exploring benefits
• Level D · Scientific groundwork from lab and animal studies
• Emerging · Emerging topic under active research

Abstract (original English)

Several factors are known to be involved in the regulation of vitamin D and sunlight and diet are the two sources in humans, but the relative importance of each of them is not well defined. Vitamin D, parathyroid hormone and serum insulin-like growth factor-I (IGF-I) were found to be independent predictors of total bone density. Thus, the growth hormone (GH)/IGF-I is thought to play an important role in the regulation of bone mineral density and the skeleton is second only to the liver as a source of circulating levels of IGF-I. The mechanisms by which IGF-I may influence bone metabolism is not fully understood but they are a predictor of bone mass density and are positively associated with vitamin D concentrations. There is a physiological decline of the GH/IGF axis with ageing. The high affinity IGF-binding proteins (IGFBP-I to 6) have also been involved in IGF-I regulation, and it is important to include the IGF-independent properties, particularly those of IGFBP3 that may be involved in the osteoblastic differentiation observed in human bone marrow stromal cell cultures. These hormones have been shown to up regulate each other. 1,25-(OH) D(3) has been shown to promote the action of IGF-I by increasing IGF-I receptors and IGF-I can also elevate 1,25-(OH) D(3) concentrations by stimulating the hydroxylation of 25-(OH) D(3) in the active 1,25-(OH) D(3) hormone. Both GH and IGF

Evidence level

Evidence from laboratory and animal studies provides groundwork for understanding mechanisms and potential before human studies continue.

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