Assessing the Relationship between Serum IGF-1 and BMI by Age in the Long Life Family Study

Background Serum levels of insulin-like growth factor 1 (IGF-1) and body mass index (BMI) are both associated with susceptibility to age-related diseases. Reports on the correlation between them have been conflicting, with both positive to negative correlations reported. However, the age ranges of the participants varied widely among these studies. Methods Using data on 4,241 participants (aged 24–110) from the Long Life Family Study, we investigated the relationship between IGF-1 and BMI by age groups using regression analysis. Results When stratified by age quartile, the correlation between IGF-1 and BMI varied: in the 1st quartile (Q1, 24 y–58 y) the correlation was negative ( r = −0.1, P = 0.0008); in Q2 (59 y– 66 y) it was negative ( r = −0.035) but non-significant; in Q3 (67 y–86 y) it was positive ( r = 0.045) but non-significant; and in Q4 (87 y–110 y) the correlation was positive ( r = 0.14, P < 0.0001). This pattern did not differ by sex. We observed a similar age-related pattern between IGF-1 and BMI among participants in the third National Health and Nutritional Examination Survey. Conclusions Our results, that the relationship between IGF-1 and BMI differs by age, may explain some of the inconsistency in reports about their relationship and encourage additional studies to understand the mechanisms underlying it. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement The work with the Long Life Family Study was supported by the National Institute on Aging at National Institutes of Health cooperative agreements U01AG023712, U01AG23744, U01AG023746, U01AG023749, U01AG023755, and U19AG063893. Support and sponsorship for R.A.S. provided by the University of Zawia and the Libyan Ministry of Higher Education through the Libyan North American Scholarship Program (LNASP). ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Visit 1 LLFS: IRB0509062 All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes the data element will be included in this manuscript is not available online.