Socioeconomic conditions across life related to multiple measures of the endocrine system in older adults: Longitudinal findings from a British birth cohort study

Abstract

Background: Little is known about how socioeconomic position (SEP) across life impacts on different axes of the endocrine system which are thought to underlie the ageing process and its adverse consequences. We examined how indicators of SEP across life related to multiple markers of the endocrine system in late midlife, and hypothesized that lower SEP across life would be associated with an adverse hormone profile across multiple axes.

Methods: Data were from a British cohort study of 875 men and 905 women followed since their birth in March 1946 with circulating free testosterone and insulin-like growth factor-I (IGF-I) measured at both 53 and 60-64 years, and evening cortisol at 60-64 years. Indicators of SEP were ascertained prospectively across life-paternal occupational class at 4, highest educational attainment at 26, household occupational class at 53, and household income at 60-64 years. Associations between SEP and hormones were investigated using multiple regression and logistic regression models.

Results: Lower SEP was associated with lower free testosterone among men, higher free testosterone among women, and lower IGF-I and higher evening cortisol in both sexes. For example, the mean standardised difference in IGF-I comparing the lowest with the highest educational attainment at 26 years (slope index of inequality) was -0.4 in men (95% CI -0.7 to -0.2) and -0.4 in women (-0.6 to -0.2). Associations with each hormone differed by SEP indicator used and sex, and were particularly pronounced when using a composite adverse hormone score. For example, the odds of having 1 additional adverse hormone concentration in the lowest compared with highest education level were 3.7 (95% CI: 2.1, 6.3) among men, and 1.6 (1.0, 2.7) among women (P (sex interaction) = 0.02). We found no evidence that SEP was related to apparent age-related declines in free testosterone or IGF-I.

Conclusions: Lower SEP was associated with an adverse hormone profile across multiple endocrine axes. SEP differences in endocrine function may partly underlie inequalities in health and function in later life, and may reflect variations in biological rates of ageing. Further studies are required to assess the likely functional relevance of these associations.

Keywords: Cortisol; Insulin-like growth factors; Socioeconomic factors; Testosterone; Thyroid.

Fig. 1

Socioeconomic position in relation to a composite hormone score at 60–64 years—odds ratios (95% CI) of being in a 1-unit higher (adverse) hormone profile score in the lowest compared with highest socioeconomic position (relative index of inequality). Note: men shown in circles, women in triangles. Hormone profile scores were calculated by adding together the number of adverse hormone concentrations recorded at 60–64 years (0, 1, 2–3). A score of 1 was given if participants were in the lowest quartile for either IGF-I, or free testosterone concentration (among men only—among women those in the highest quartile were given a score of 1), or the highest quartile of evening cortisol concentration. Odds ratios were calculated using ordered logistic regression. Sample sizes were as follows: paternal occupational class (648 men, 682 women), education (638/690), occupational class (670/703), household income (656/689), and lifetime SEP score (601/609); #p-value for sex interaction term <0.05.