Social Differences in Insulin-like Growth Factor-1: Findings from a British Birth Cohort

When in the lifecourse? Socioeconomic position across the lifecourse and biological health score

PURPOSE

Educational attainment is associated with multiphysiological wear and tear. However, associations with measures of socioeconomic position (SEP) across different life-stages are not established.

METHODS

Using regression models and data from 8105 participants from the UK Household Longitudinal Study (Understanding Society), we examined associations of lifecourse SEP with an overall biological health score (BHS). BHS is broader than usual measures of biological 'wear and tear' and is based on six physiological subsystems (endocrine, metabolic, cardiovascular, inflammatory/immune, liver, and kidney), with higher scores indicating worse health. Lifecourse SEP was based on respondents' parental, first, and most recent occupations.

RESULTS

Associations with SEP at all life-stages demonstrated higher BHS with increasing disadvantage (e.g. slope index of inequality (SII) (95 % CI) for most recent SEP: 0.04 (0.02, 0.06)). There was little difference in the magnitude of associations for SEP measured at each life-stage. Cumulative disadvantage across the lifecourse showed a stepped association with increasing BHS (SII (95 % CI): 0.05 (0.04, 0.07)). Associations were largely driven by metabolic, cardiovascular, and inflammatory systems.

CONCLUSION

Our results suggest that disadvantaged SEP across the lifecourse contributes cumulatively to poorer biological health, highlighting that every life-stage should be a target for public health policies and intervention.

The neurobiology of insulin-like growth factor I: From neuroprotection to modulation of brain states

After decades of research in the neurobiology of IGF-I, its role as a prototypical neurotrophic factor is undisputed. However, many of its actions in the adult brain indicate that this growth factor is not only involved in brain development or in the response to injury. Following a three-layer assessment of its role in the central nervous system, we consider that at the cellular level, IGF-I is indeed a bona fide neurotrophic factor, modulating along ontogeny the generation and function of all the major types of brain cells, contributing to sculpt brain architecture and adaptive responses to damage. At the circuit level, IGF-I modulates neuronal excitability and synaptic plasticity at multiple sites, whereas at the system level, IGF-I intervenes in energy allocation, proteostasis, circadian cycles, mood, and cognition. Local and peripheral sources of brain IGF-I input contribute to a spatially restricted, compartmentalized, and timed modulation of brain activity. To better define these variety of actions, we consider IGF-I a modulator of brain states. This definition aims to reconcile all aspects of IGF-I neurobiology, and may provide a new conceptual framework in the design of future research on the actions of this multitasking neuromodulator in the brain.

Circulating insulin-like growth factor I modulates mood and is a biomarker of vulnerability to stress: from mouse to man

Individual susceptibility to anxiety disorders after maladaptive responses to stress is not well understood. We now report that while exploring stress responses in mice after traumatic brain injury (TBI), a condition associated to stress susceptibility, we observed that the anxiogenic effects of either TBI or exposure to life-threatening experiences (predator) were blocked when both stressors were combined. Because TBI increases the entrance into the brain of serum insulin-like growth factor I (IGF-I), a known modulator of anxiety with a wide range of concentrations in the human population, we then determined whether circulating IGF-I is related to anxiety measures. In mice, anxiety-like responses to predator were inversely related to circulating IGF-I levels. Other indicators of mood regulation such as sensitivity to dexamethasone suppression and expression levels of blood and brain FK506 binding protein 5 (FKBP5), a co-chaperone of the glucocorticoid receptor that regulates its activity, were also associated to circulating IGF-I. Indeed, brain FKBP5 expression in mice was stimulated by IGF-I. In addition, we observed in a large human cohort (n = 2686) a significant relationship between plasma IGF-I and exposure to recent stressful life events, while FKBP5 expression in blood cells was significantly associated to plasma IGF-I levels. Collectively, these data indicate that circulating IGF-I appears to be involved in mood homeostasis across different species. Furthermore, the data in mice allow us to indicate that IGF-I may be acting at least in part by modulating FKBP5 expression.

Physiological wear-and-tear and later subjective health in mid-life: Findings from the 1958 British birth cohort

OBJECTIVE

Our body adapts continuously to environmental challenges and stressful conditions. Allostatic load (AL) is a concept that aims to capture the overall physiological wear-and-tear of the body triggered by the repeated activation of compensatory physiological mechanisms as a response to chronic stress. Growing evidence has shown a link between AL and later health decline, morbidity and mortality. However, due to the global physiological effect captured by the AL concept, it is particularly pertinent to examine its association with subsequent health by taking a broad definition of the latter. We examined the association between AL at 44 years and general health as measured by a latent multidimensional measure of subjective health at 50 years integrating sleep patterns, physical and mental health.

METHODS

AL was constructed using 14 biomarkers representing four physiological systems on 7573 members of the 1958 British birth cohort. Health status was captured using self-reported information about subjective health and summarized using a principal component analysis including: seven dimensions of the SF-36 questionnaire of health-related quality of life, the sleep subscale of the Medical Outcomes Study characterizing quality of sleep patterns, and a malaise inventory score detecting depressive symptoms.

RESULTS

Higher AL score was gradually associated with worse subjective health, after taking into account classic confounders.

CONCLUSIONS

Using a physiological index to grasp how the environment can "get under the skin" leading to poor health is of great interest, permitting a better understanding of life course origins of disease and social gradients in health.

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

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.

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Socioeconomic position (SEP) across life was related to multiple hormone measures.

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Lower SEP was related to lower testosterone in men, higher testosterone in women.

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Lower SEP was related to lower IGF-I and higher evening cortisol in both sexes.

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SEP differences in multiple hormone axes may underlie later life health inequality.

Sex, Sport, IGF-1 and the Community Effect in Height Hypothesis

We test the hypothesis that differences in social status between groups of people within a population may induce variation in insulin-like growth factor-1(IGF-1) levels and, by extension, growth in height. This is called the community effect in height hypothesis. The relationship between IGF-1, assessed via finger-prick dried blood spot, and elite level sport competition outcomes were analysed for a sample of 116 undergraduate men and women. There was a statistically significant difference between winners and losers of a competition. Winners, as a group, had higher average pre-game and post-game IGF-1 levels than losers. We proposed this type of difference as a proxy for social dominance. We found no evidence that winners increased in IGF-1 levels over losers or that members of the same team were more similar in IGF-1 levels than they were to players from other teams. These findings provide limited support toward the community effect in height hypothesis. The findings are discussed in relation to the action of the growth hormone/IGF-1 axis as a transducer of multiple bio-social influences into a coherent signal which allows the growing human to adjust and adapt to local ecological conditions.

Adverse childhood experiences and physiological wear-and-tear in midlife: Findings from the 1958 British birth cohort

Allostatic load (AL) is a measure of overall physiological wear-and-tear over the life course, which could partially be the consequence of early life exposures. AL could allow a better understanding of the potential biological pathways playing a role in the construction of the social gradient in adult health. To explore the biological embedding hypothesis, we examined whether adverse childhood experiences (ACEs) are associated with elevated AL in midlife. We used imputed data on 3,782 women and 3,753 men of the National Child Development Study in Britain followed up seven times. ACEs were measured using prospective data collected at ages 7, 11, and 16. AL was operationalized using data from the biomedical survey collected at age 44 on 14 parameters representing four biological systems. We examined the role of adult health behaviors, body mass index (BMI), and socioeconomic status as potential mediators using a path analysis. ACEs were associated with higher AL for both men and women after adjustment for early life factors and childhood pathologies. The path analysis showed that the association between ACEs and AL was largely explained by early adult factors at age 23 and 33. For men, the total mediated effect was 59% (for two or more ACEs) via health behaviors, education level, and wealth. For women, the mediated effect represented 76% (for two or more ACEs) via smoking, BMI, education level, and wealth. Our results indicate that early psychosocial stress has an indirect lasting impact on physiological wear-and-tear via health behaviors, BMI, and socioeconomic factors in adulthood.

Modeling determinants of growth: evidence for a community-based target in height?

BACKGROUND

Human growth is traditionally envisaged as a target-seeking process regulated by genes, nutrition, health, and the state of an individual's social and economic environment; it is believed that under optimal physical conditions, an individual will achieve his or her full genetic potential.

METHODS

Using a panel data set on individual height increments, we suggest a statistical modeling approach that characterizes growth as first-order trend stationary and allows for controlling individual growth tempo via observable measures of individual maturity. A Bayesian framework and corresponding Markov-chain Monte Carlo techniques allowing for a conceptually stringent treatment of missing values are adapted for parameter estimation.

RESULTS

The model provides evidence for the adjustment of the individual growth rate toward average height of the population.

CONCLUSION

The increase in adult body height during the past 150 y has been explained by the steady improvement of living conditions that are now being considered to have reached an optimum in Western societies. The current investigation questions the notion that the traditional concept in the understanding of this target-seeking process is sufficient. We consider an additional regulator that possibly points at community-based target seeking in growth.

Psychosocial biomarker research: integrating social, emotional and economic factors into population studies of aging and health

There are complex reciprocal relationships between health and social, emotional and economic factors in aging populations. Social and affective neurosciences are rapidly developing an understanding of the mechanisms underlying these phenomena using sophisticated behavioural, neuroimaging and psychophysiological methods. These techniques are often complex and expensive, so are generally used in relatively small selected samples rather than in large-scale cohort studies. However, an understanding of the significance of these processes in health and well-being depends on integrating findings from social and affective neuroscience into population-level studies. The aim of this article is to describe how a population perspective on the determinants of health and well-being in old age articulates with the agenda of social, affective and economic neuroscience, particularly through the application of psychosocial biomarker research. Social and affective neuroscience and epidemiological approaches provide complementary research strategies for understanding the mechanisms linking social, emotional and economic factors with health risk. This will be illustrated primarily from findings from two studies conducted at University College London, the Whitehall II Study and the English Longitudinal Study of Ageing.

Cognitive and social functions and growth factors in a mouse model of Rett syndrome

Rett syndrome (RTT) is an autism-spectrum disorder caused by mutations in the X-linked gene encoding methyl-CpG-binding protein 2 (MeCP2). Abnormalities in social behavior, stereotyped movements, and restricted interests are common features in both RTT and classic autism. While mouse models of both RTT and autism exist, social behaviors have not been explored extensively in mouse models of RTT. Here, we report cognitive and social abnormalities in Mecp2(1lox) null mice, an animal model of RTT. The null mice show severe deficits in short- and long-term object recognition memories, reminiscent of the severe cognitive deficits seen in RTT girls. Social behavior, however, is abnormal in that the null mice spend more time in contact with stranger mice than do wildtype controls. These findings are consistent with reports of increased reciprocal social interaction in RTT girls relative to classic autism. We also report here that the levels of the neurotrophins brain-derived neurotrophic factor (BDNF), insulin-like growth factor-1 (IGF-1), and nerve growth factor (NGF) are decreased in the hippocampus of the null mice, and discuss how this may provide an underlying mechanism for both the cognitive deficits and the increased motivation for social contact observed in the Mecp2(1lox) null mice. These studies support a differential etiology between RTT and autism, particularly with respect to sociability deficits.