Diet, body composition, and physical fitness influences on IGF-I bioactivity in women

OBJECTIVE: Insulin-like growth factor I (IGF-I) is a metabolic-regulatory hormone that mediates a variety of physiologic functions. Body composition, fitness status and intake of certain micro- and macronutrients are associated with circulating concentrations of immunoreactive IGF-I. The influence of these factors on IGF-I bioactivity; however, is undetermined. We assessed the relationships between IGF-I bioactivity and lifestyle factors purportedly associated with IGF-I immunoreactivity.

DESIGN: In a cross sectional study, fasted blood samples were obtained from 44 lightly active, college-age (20+/-2 yrs) women. IGF-I bioactivity was estimated by an assay which determines the ability of serum IGFs to phosphorylate IGF-I receptors in cultured cells; free and total IGF-I were measured by immunoassay. Estradiol and progesterone were measured by immunoassay. Body mass index was calculated from measured height and weight, bone mineral density and body fat percentage measured by dual energy X-ray absorptiometry, and peak oxygen consumption (VO(2peak)) determined during a graded treadmill protocol. A food frequency questionnaire measured habitual and a 5-day food record assessed short-term micro- and macronutrient intakes. Associations between bioactive, free and total IGF-I with body composition, sex hormones, VO(2peak), and dietary intake were assessed using univariate and multiple linear regression analyses.

RESULTS: Associations between bioactive IGF-I with age (r=-0.36, P<0.05), body fat percentage (r=-0.32, P<0.05), estradiol (r=0.31, P<0.05) and progesterone (r=0.33, P<0.05) concentrations, habitual alcohol (r=-0.38, P<0.05) and selenium intakes (r=0.41, P<0.01), free IGF-I with age (r=-0.34, P<0.05), estradiol (r=0.48, P<0.01) and progesterone (r=0.52, P<0.001) concentrations, habitual alcohol (r=-0.33, P<0.05) and isoflavone intakes (r=0.30, P<0.05) and total IGF-I with age (r=-0.27, P<0.05) and habitual alcohol intake (r=-0.33, P<0.05) were observed. Habitual alcohol intake was a negative predictor of bioactive, free and total IGF-I in multivariate models.

CONCLUSION: Of the lifestyle factors measured, the most robust relationship observed was a negative association between habitual alcohol intake and all measures of IGF-I. This finding suggests that alcohol intake may blunt the physiologic actions of the IGF-I axis.