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Circulating insulin, insulin-like growth factor binding protein 1 (IGFBP-1) and leptin are modified by obesity and have been associated with certain cancers in past studies. We conducted a cross-sectional study to better describe the correlation of these proteins with age, gender, anthropometric indices and lifestyle and dietary factors. C-peptide was used as a more stable measure of insulin secretion. We measured fasting plasma levels of all three proteins in a random sample of 1000 MEC participants (100 for each of ten sex/ethnic groups, excluding subjects who reported estrogen replacement therapy use at time of blood draw or prevalent breast, prostate or colorectal cancer. Using multiple regression, we found in a preliminary analysis that race/ethnicity, BMI, age and energy intake were independently associated with IGFBP-1 in females. In males, race/ethnicity, BMI, age and protein intake were independently associated with IGFBP-1 and there was a significant negative interaction between Japanese race/ethnicity and BMI. Race/ethnicity, BMI and energy intake were independently associated with leptin in females. In males, race/ethnicity, BMI and hours of vigorous activity were significantly associated with leptin and there was a positive interaction between Japanese race/ethnicity and BMI. For C-peptide, race/ethnicity, BMI and protein intake showed independent associations in both females and males. There was also a positive interaction between Japanese race/ethnicity and BMI among males for C-peptide. In this cross-sectional analysis of lifestyle and dietary correlates of IGFBP-1, leptin and C-peptide, race/ethnicity and BMI were the strongest determinants of all three protein levels. These results provide impetus to carefully investigate the interaction between race/ethnicity and obesity in determination of these circulating protein levels.

[Proc Amer Assoc Cancer Res, Volume 47, 2006]