Annals of Epidemiology
Volume 18, Issue 8, August 2008, Pages 664-670
Social Differences in Insulin-like Growth Factor-1: Findings from a British Birth Cohort
Meena Kumaria et al.
Insulin-like growth factor-1 (IGF-1) is related to factors that are socially patterned and may play a role in social differences in the development of morbidities including disability. Our aim is to examine whether there are social differences in IGF-1 in a cohort of participants between 44 and 45 years of age.
We examine the association of IGF-1 with social position measured by father's or own occupational class at three time points in childhood and adulthood, in a cohort of individuals born in one month in 1958 (N = 3,374 men and 3,302 women).
Lower IGF-1 levels were associated with lower social position measured with father's occupational class at birth (p < 0.0001) and own occupational class aged 42 years (p < 0.001). Adult social position was associated with IGF-1 independently of social position at birth (p < 0.001) or any covariates examined. Conclusions IGF-1 secretion is associated with social position such that low social position is associated with lower levels of IGF-1. This biomarker may play a role in the development of social differences in morbidities associated with aging, such as the development of disability.
Key Words: Socioeconomic Status; Life Course; Inequalities in Health; Birth Cohort; Insulin-like Growth Factor–1
Abbreviations: IGF-1, insulin-like growth factor–1; BMI, body mass index; HbA1c, glycosylated hemoglobin
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Insulin-like growth factor–1 (IGF-1) is an anabolic protein, related to insulin, which has important actions on cell division, metabolism, as well as on cell proliferation in vascular smooth muscle. Low levels of IGF-1 are associated with atherosclerosis and may be predictive of cardiovascular events (1), type 2 diabetes (2), loss of physical functioning (3), whereas high levels of IGF-1 are associated with the development of certain cancers (2).
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Heart disease (1), diabetes (2), functioning, or disability (3) show associations with social position, and our findings suggest that IGF-1 may play a role in the pathways that mediate these differences. This is interesting in light of the recent increase in the prevalence of type 2 diabetes and in the context of an aging population with the resultant increases in disability and poor functioning. An independent association with disability may be mediated by IGF-1 because low IGF-1 levels may correspond to a decrease in the ability to maintain muscle mass (42). Further investigation into the predictors of high IGF-1 levels may help to identify predictors for the maintenance of muscle mass that may militate against the development of disability.
A related (?) finding from an older study:
Female facial attractiveness was best predicted by BMI and past health problems, whereas male facial attractiveness was best predicted by the socioeconomic status (SES) of their rearing environment.
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Good genes theory predicts that variables contributing positively to individual health and fitness should be positively related to each other, and negatively related to variables that impact negatively on health and fitness. In this study, “positive” variables are SES and attractiveness, and “negative” variables are BMI, asymmetry and Health Problems. The results of between-variables correlations are thus generally consistent with good genes theory, although not all correlations were significant (Table 2).