Circulating insulin-like growth factor 1 and insulin-like growth factor binding protein-3 level in Alzheimer's disease: a meta-analysis.

It has been reported that the associations between circulating insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) and Alzheimer's disease (AD) are controversial. Thus, present meta-analysis was carried out to confirm the probable associations. We searched "PubMed", "Springer" and "Medline" databases using the term ("insulin-like growth factor-1" or "IGF-1" or "insulin-like growth factor binding protein-3" or "IGFBP-3") and ("Alzheimer's disease") until April 2016. Furthermore, standard mean differences (SMDs) were calculated. A total of seven reports involving 1342 percipients were pooled. SMDs were -0.25 (P = 0.22) and -0.33 (P = 0.08) for IGF-1 and IGFBP-3, respectively. Furthermore, the circulating IGF-1 levels in AD patients were lower than controls when studies with the difference of mean age ≤1 year (SMD -0.57, P = 0.007) or 2 years (SMD -0.58, P = 0.02) or difference of mean MMSE scores ≤10 scores (SMD -0.94, P < 0.00001), or studies from Europe (SMD -0.89, P < 0.00001) were excluded. In addition, the circulating IGFBP-3 levels in AD patients were lower than controls when studies with the difference of mean age ≤2 years (SMD -0.62, P = 0.006) or difference of mean MMSE scores ≤6 scores (SMD -0.48, P = 0.0004), 7 scores (SMD -0.58, P = 0.02), or 8 scores (SMD -0.80, P = 0.03) were excluded. Even though no significant difference of circulating IGF-1 and IGFBP-3 levels in AD patients comparing with controls was found in present meta-analysis, the current study provided the evidence that the circulating IGF-1 and IGFBP-3 level in AD patients were influenced by the difference of mean age as well as MMSE scores. Furthermore, circulating IGFBP-3 levels in AD patients may be decreased earlier than IGF-1.