Increase in epinephrine excretion is associated with cognitive decline in elderly men: MacArthur studies of successful aging

Cognitive impairment in heart failure patients: association with abnormal circadian blood pressure rhythm: a review from the HOPE Asia Network

Cognitive impairment (CI) is frequently a comorbid condition in heart failure (HF) patients, and is associated with increased cardiovascular events and death. Numerous factors contribute to CI in HF patients. Decreased cerebral blood flow, inflammation, and activation of neurohumoral factors are all thought to be factors that exacerbate CI. Hypoperfusion of the brain due to decreased systemic blood flow, cerebral venous congestion, and atherosclerosis are the main mechanism of CI in HF patients. Abnormal circadian BP rhythm is one of the other conditions associated with CI. The conditions in which BP does not decrease sufficiently or increases during the night are called non-dipper or riser BP patterns. Abnormal circadian BP rhythm worsens CI in HF patients through cerebral congestion during sleep and atherosclerosis due to pressure overload. Interventions for CI in HF patients include treatment for HF itself using cardiovascular drugs, and treatment for fluid retention, one of the causes of abnormal circadian rhythms. Proposed pathways of cognitive impairment in heart failure through abnormal circadian blood pressure rhythm.

Greater anhedonia scores in healthy individuals are associated with less decline in 24-hour energy expenditure with fasting: Evidence for a link between behavioral traits and spendthrift phenotype

Obesity rates are increasing and affecting mental health. It is important to understand how behavioral traits such as anhedonia are associated with physiologic traits that may predict weight-change in clinical and non-clinical populations. We studied whether 24-hour energy expenditure (24hEE) changes with fasting and overfeeding are associated with anhedonia in a healthy cohort. We performed behavioral assessments (physical anhedonia scale (PAS) and inventory for depressive symptoms (IDS)) followed by measures of 24hEE and urinary catecholamines in a whole-room indirect calorimeter (respiratory chamber) during energy balance, and then randomly during fasting and 2 different overfeeding diets. Participants (n=98) were medically healthy, between 18 and 55 years of age, with normal glucose regulation and weight-stable 6 months before admission. Women were premenopausal and not pregnant. Higher PAS was significantly associated with lesser decrease in 24hEE with fasting and higher urinary catecholamine excretion rates - consistent with spendthrift metabolism. As IDS increased, the association between anhedonia and the change in 24hEE from energy balance to fasting decreased (B-values were lower for change in EE). Here, higher PAS scores may reflect the ability to respond with appropriate homeostatic reactions which balance energy needs. IDS scores blunting this response may explain how anhedonia and depression can lead to weight gain.

Level of urinary catecholamine in children with Sleep Disordered Breathing: A systematic review and meta-analysis

OBJECTIVE

To compare the levels of different urinary catecholamines amongst paediatric patients with and without sleep-disordered breathing (SDB).

METHODS

Literature searches were conducted on PubMed and EMBASE until 25/06/2022. Inclusion criteria were original human studies, English language, paediatric subjects diagnosed with SDB/obstructive sleep apnoea (OSA). The quality of studies was assessed by the Newcastle-Ottawa Quality Assessment (NOSGEN). The registered number of this study on the International Prospective Register of Systematic Reviews (PROSPERO) is CRD42022332939. The main outcome measured was standardised mean difference (SMD) of urinary catecholamine between subjects with and without SDB, between those with and without OSA, and also between subjects with mild OSA and those with moderate/ severe OSA. Sensitivity analyses were performed to avoid bias.

RESULTS

9 studies (8 cross-sectional and 1 cohort study) with a total of 838 subjects, were included in the quantitative analysis. Urine level of noradrenaline was higher in patients with SDB, which included primary snoring (PS), when compared to controls: SMD = 0.86 (95%CI=0.32-1.41; I²=85%, P=0.002). The levels of urinary noradrenaline and adrenaline were higher in children with OSA when compared to controls: SMD = 1.45 (95%CI=0.91-2.00; I²=75%, P < 0.001); SMD = 1.84 (0.00-3.67; I²=97%, P=0.05). Urine level of noradrenaline was higher in subjects with moderate/severe OSA compared to the mild OSA: SMD = 0.55 (95%CI=0.10-1.00; I²=0%, P=0.02). Urinary dopamine was not associated with SDB regardless of severity.

CONCLUSIONS

Urinary noradrenaline was higher in all patients with SDB. Subjects with OSA, a more severe form of SDB, had higher urine levels of noradrenaline and adrenaline. Hence, noradrenaline and adrenaline may be markers of sympathetic overtone in patients with SDB and could potentially act as surrogate markers for SDB complications. Further studies are needed to assess this association.

Diurnal dynamic range as index of dysregulation of system dynamics. A cortisol examplar using data from the Study of Midlife in the United States

We discuss the importance of including measures of dysregulated system dynamics in the operationalization of allostatic load. The concept of allostatic load, as originally proposed by McEwen and Stellar, included dysregulation not only in the resting state of physiological systems, but also in system dynamics. We describe previous work on cortisol diurnal dynamic range (peak to nadir spread) as an index of the health of the hypothalamic-pituitary-adrenal axis, with compression of dynamic range being a marker of dysregulation. In particular, we review the evidence for a) diurnal dynamic range compression in people from disadvantaged backgrounds, b) cross-sectional association of cortisol diurnal dynamic range compression with dysregulation in other systems' resting states, and c) cross-sectional association of cortisol diurnal dynamic range compression with lower scores on cognitive testing. Then, we present new data from the Study of Midlife in the United States (MIDUS) on longitudinal associations of cortisol dynamic range compression with subsequent cognitive decline and all-cause mortality. Briefly, each standard deviation decrement in cortisol diurnal dynamic range is associated with adjusted mortality hazard ratio of 1.35 (95% confidence interval: 1.19, 1.54). Among those who scored at median or lower in executive functioning at baseline and survive, each standard deviation decrement in cortisol dynamic range is associated with 1% greater decline in executive functioning over a decade (95% confidence interval: 0.4%, 2.0%). We conclude that including measures of system dynamics like diurnal dynamic range in the next generation of allostatic load measurement will likely advance understanding of the cumulative physiological burden of chronic stress and life experiences, and improve the prediction of future health consequences.

Positive Effect of Cognitive Reserve on Episodic Memory, Executive and Attentional Functions Taking Into Account Amyloid-Beta, Tau, and Apolipoprotein E Status

Studies exploring the simultaneous influence of several physiological and environmental factors on domain-specific cognition in late middle-age remain scarce. Therefore, our objective was to determine the respective contribution of modifiable risk/protective factors (cognitive reserve and allostatic load) on specific cognitive domains (episodic memory, executive functions, and attention), taking into account non-modifiable factors [sex, age, and genetic risk for Alzheimer's disease (AD)] and AD-related biomarker amount (amyloid-beta and tau/neuroinflammation) in a healthy late-middle-aged population. One hundred and one healthy participants (59.4 ± 5 years; 68 women) were evaluated for episodic memory, executive and attentional functioning via neuropsychological test battery. Cognitive reserve was determined by the National Adult Reading Test. The allostatic load consisted of measures of lipid metabolism and sympathetic nervous system functioning. The amyloid-beta level was assessed using positron emission tomography in all participants, whereas tau/neuroinflammation positron emission tomography scans and apolipoprotein E genotype were available for 58 participants. Higher cognitive reserve was the main correlate of better cognitive performance across all domains. Moreover, age was negatively associated with attentional functioning, whereas sex was a significant predictor for episodic memory, with women having better performance than men. Finally, our results did not show clear significant associations between performance over any cognitive domain and apolipoprotein E genotype and AD biomarkers. This suggests that domain-specific cognition in late healthy midlife is mainly determined by a combination of modifiable (cognitive reserve) and non-modifiable factors (sex and age) rather than by AD biomarkers and genetic risk for AD.

Association of working memory and elevated overnight urinary norepinephrine in patients with schizophrenia

INTRODUCTION

Norepinephrine has both central and peripheral origins and is known to influence cognitive processes in attention, learning, and working memory, but the research regarding the impact of norepinephrine on cognition in schizophrenia remains sparse, and mainly focuses on centrally regulated noradrenergic effects. This study examined the relationship between cumulative overnight norepinephrine levels in the urine and working memory in patients with schizophrenia and healthy controls.

METHODS

Urinary catecholamines were collected overnight in patients with schizophrenia (n = 75) and healthy controls (n = 33). Working memory was assessed using the digit sequencing task.

RESULTS

Patients showed significantly higher average levels of overnight norepinephrine (t(103.10) = -3.16, p = 0.002) and reduced working memory performance (t(90) = 3.87, p = 0.001) compared with healthy individuals. There was a significant negative correlation between norepinephrine and working memory in patients (r = -0.38, p = 0.005), but not in controls (r = 0.08, p = 0.67). After controlling for age, sex, antipsychotic medications, and serotonin-norepinephrine reuptake inhibitor-based antidepressants, the correlation remained significant (r = -0.41, p = 0.004).

CONCLUSIONS

High peripheral overnight levels of urinary norepinephrine are associated with lower working memory performance in patients with schizophrenia. These results parallel previous studies suggesting that high levels of central norepinephrine may result in working memory impairments. As norepinephrine rapidly breaks down and usually does not pass through the blood-brain barrier, the potential effect of peripheral cumulative norepinephrine on working memory is intriguing, and needs to be further investigated.

The effects of stress on cardiovascular disease and Alzheimer's disease: Physical exercise as a counteract measure

AD is a complicated multi-systemic neurological disorder that involves different biological pathways. Several risk factors have been identified, including chronic stress. Chronic stress produces an alteration in the activity of the hypothalamic pituitary adrenal (HPA) system, and the autonomic nervous system (ANS), which over time increase the risk of AD and also the incidence of cardiovascular disease (CVD) and risk factors, such as hypertension, obesity and type 2 diabetes, associated with cognitive impairment and AD. Considering the multi-factorial etiology of AD, understanding the complex interrelationships between different risk factors is of potential interest for designing adequate strategies for preventing, delaying the onset or slowing down the progression of this devastating disease. Thus, in this review we will explore the general mechanisms and evidence linking stress, cardiovascular disease and AD, and discuss the potential benefits of physical activity for AD by counteracting the negative effects of chronic stress, CVD and risk factors.

Cognitive efficiency in late midlife is linked to lifestyle characteristics and allostatic load

We investigated whether cognitive fitness in late midlife is associated with physiological and psychological factors linked to increased risk of age-related cognitive decline. Eighty-one healthy late middle-aged participants (mean age: 59.4 y; range: 50-69 y) were included. Cognitive fitness consisted of a composite score known to be sensitive to early subtle cognitive change. Lifestyle factors (referenced below as cognitive reserve factors; CRF) and affective state were determined through questionnaires, and sleep-wake quality was also assessed through actimetry. Allostatic load (AL) was determined through a large range of objective health measures. Generalized linear mixed models, controlling for sex and age, revealed that higher cognitive reserve and lower allostatic load are related to better cognitive efficiency. Crystallized intelligence, sympathetic nervous system functioning and lipid metabolism were the only sub-fields of CRF and AL to be significantly associated with cognition. These results show that previous lifestyle characteristics and current physiological status are simultaneously explaining variability in cognitive abilities in late midlife. Results further encourage early multimodal prevention programs acting on both of these modifiable factors to preserve cognition during the aging process.

Heart Failure-Induced Brain Injury

Heart failure (HF) is a systemic illness with grave implications for bodily functions. The brain, among other vital organs, often suffers insults as a result of HF, and both anatomic and functional brain abnormalities were found in the HF population. This injury was demonstrated across a wide range of clinical conditions and cardiac functions and was shown to affect patients' outcomes. Although reduced cardiac output and high burden of cardiovascular risk factors are the prevailing explanations for these findings, there are data showing the involvement of neurohormonal, nutritional, and inflammatory mechanisms in this complex process. Here, the authors review the suggested pathophysiology behind brain injury in HF, describe its effect on patients' outcomes, offer a diagnostic approach, and discuss possible therapeutic options.

Feasibility of 24-Hr Urine Collection for Measurement of Biomarkers in Community-Dwelling Older Adults

Biologic markers are becoming a key part of gerontological research, including their measurement at multiple intervals to detect changes over time. This report examined the feasibility and quality of 24-hr urine collection to measure neuroendocrine biomarkers in a community-based sample of older caregivers and non-caregivers. At each interview, participants were instructed on the correct method to collect and store the sample. As incentives, participants selected a day for urine collection within 5 days of the interview, received a reimbursement, and study staff travelled to their home to retrieve the specimen. Between 2008 and 2013, 256 participants were enrolled; all but two participants (99%) provided a baseline urine specimen, of which 93% were considered adequate. Urine collection and quality remained high over three annual follow-up interviews and did not vary by caregiver status or perceived stress level. Our results indicate that 24-hr urine collection is feasible in active, community-dwelling older adults.

DOES LOWER SUBJECTIVE SOCIAL STATUS YIELD RISKIER BIOMARKER PROFILES?

Both objective and, more recently, subjective measures of low social status have been linked to poor health outcomes. It is unclear, however, through which precise physiological mechanisms such standing may influence health, although it has been proposed that those of lower status may have biomarker profiles that are more dysregulated (and hence pose a greater risk for poorer health). The main objective of this study was to investigate whether lower subjective social standing is associated with riskier neuroendocrine biomarker profiles. Data were from the Social Environment and Biomarkers of Aging Study (SEBAS), a nationally representative survey of Taiwanese men and women (ages 54-91) conducted in Taiwan in 2000. Five neuroendocrine markers (cortisol, dehydroepiandrosterone sulphate (DHEAS), adrenaline, noradrenaline and dopamine) were analysed both separately and collectively in an index termed neuroendocrine allostatic load (NAL) in relation to status - both self-reported and as measured through objective socioeconomic status (SES) indicators. For the biomarker DHEAS, some connection was found between its levels and the measures of status, but for the other markers and the NAL index almost no connection was found. The overall negative finding of this paper would be further supported with more and different measures of neuroendocrine system function and a reordering of the subjective social status questions in the survey such that the one probing about status in the community (that has no prompt) was asked before the one probing about status in all of Taiwan (which has a SES prompt).

Tunable stringency aptamer selection and gold nanoparticle assay for detection of cortisol

The first-known aptamer for the stress biomarker cortisol was selected using a tunable stringency magnetic bead selection strategy. The capture DNA probe immobilized on the beads was systematically lengthened to increase the number of bases bound to the complementary pool primer regions following selection enrichment. This resulted in a single sequence (15-1) dominating the final round 15 pool, where the same sequence was the second-highest copy number candidate in the enriched pool with the shorter capture DNA probe (round 13). A thorough analysis of the next-generation sequencing results showed that a high copy number may only correlate with enhanced affinity under certain stringency and enrichment conditions, in contrast with prior published reports. Aptamer 15-1 demonstrated enhanced binding to cortisol (K(d) = 6.9 ± 2.8 μM by equilibrium dialysis; 16.1 ± 0.6 μM by microscale thermophoresis) when compared with the top sequence from round 13 and the negative control progesterone. Whereas most aptamer selections terminate at the selection round demonstrating the highest enrichment, this work shows that extending the selection with higher stringency conditions leads to lower amounts eluted by the target but higher copy numbers of a sequence with enhanced binding. The structure-switching aptamer was applied to a gold nanoparticle assay in buffer and was shown to discriminate between cortisol and two other stress biomarkers, norepinephrine and epinephrine, and a structurally analogous biomarker of liver dysfunction, cholic acid. We believe this approach enhances aptamer selection and serves as proof-of-principle work toward development of point-of-care diagnostics for medical, combat, or bioterrorism targets.

Biological correlates of adult cognition: midlife in the United States (MIDUS)

Multiple biological processes are related to cognitive impairment in older adults, but their combined impact on cognition in midlife is not known. Using an array of measurements across key regulatory physiological systems and a state-of-the-art cognition battery that is sensitive to early changes, in a large, national sample of middle-aged and older adults, we examined the associations of individual biological systems and a combined, multi-system index, allostatic load, with cognitive performance. Allostatic load was strongly inversely associated with performance in both episodic memory and executive function. Of 7 biological systems, only the cardiovascular system was associated inversely with both; inflammation was associated inversely with episodic memory only, and glucose metabolism with executive function only. The associations of allostatic load with cognition were not different by age, suggesting that the implications of high allostatic load on cognitive functioning are not restricted to older adults. Findings suggest that a multi-system score, like allostatic load, may assist in the early identification of adults at increased risk for cognitive impairment.

Does depression impact cognitive impairment in patients with heart failure?

Prevalence studies have noted the cooccurrence of cognitive decline and depression in persons with heart failure. Cognitive impairment is associated with significant mortality and deteriorated quality of life, likely due to impairments in memory and executive function, which impact a patient's ability to understand and comply with prescribed treatment plans. This is especially true in complex diseases such as heart failure. Evidence from literature supports the possibility of a pathophysiological relationship between cognitive impairment, depression, and heart failure. Yet, very few studies have sought to investigate this relationship. This paper reviews current literature on the association between depression and cognitive impairment in persons with heart failure and explores possible mechanisms explaining this complex triad.

Does physical activity reduce risk for Alzheimer's disease through interaction with the stress neuroendocrine system?

Lack of physical activity (PA) is a risk factor for Alzheimer's disease (AD), and PA interventions are believed to provide an effective non-pharmacological approach for attenuating the symptoms of this disease. However, the mechanism of action of these positive effects is currently unknown. It is possible that the benefits may be at least partially mediated by the effects on the neuroendocrine stress system. Chronic stress can lead to dysfunction of the hypothalamic-pituitary-adrenal (HPA) axis, leading to aberrant basal and circadian patterns of cortisol secretion and a cascade of negative downstream events. These factors have been linked not only to reduced cognitive function but also increased levels of amyloid-β plaques and protein tau "tangles" (the neuropathological hallmarks of AD) in the non-demented mouse models of this disease. However, there is evidence that PA can have restorative effects on the stress neuroendocrine system and related risk factors relevant to AD. We explore the possibility that PA can positively impact upon AD by restoring normative HPA axis function, with consequent downstream effects upon underlying neuropathology and associated cognitive function. We conclude with suggestions for future research to test this hypothesis in patients with AD.

The clinical implications of cognitive impairment and allostatic load in bipolar disorder

BACKGROUND

Allostatic load (AL) relates to the neural and bodily "wear and tear" that emerge in the context of chronic stress. This paper aims to provide clinicians with a comprehensive overview of the role of AL in patophysiology of bipolar disorder (BD) and its practical implications.

METHODS

PubMed searches were conducted on English-language articles published from 1970 to June 2011 using the search terms allostatic load, oxidative stress, staging, and bipolar disorder cross-referenced with cognitive impairment, comorbidity, mediators, prevention.

RESULTS

Progressive neural and physical dysfunction consequent to mood episodes in BD can be construed as a cumulative state of AL. The concept of AL can help to reconcile cognitive impairment and increased rates of clinical comorbidities that occur over the course of cumulative BD episodes.

CONCLUSIONS

Data on transduction of psychosocial stress into the neurobiology of mood episodes converges to the concept of AL. Mood episodes prevention would not only alleviate emotional suffering, but also arrest the cycle of AL, cognitive decline, physical morbidities and, eventually, related mortality. These objectives can be achieved by focusing on effective prophylaxis from the first stages of the disorder, providing mood-stabilizing agents and standardized psychoeducation and, potentially, addressing cognitive deficits by the means of specific medication and neuropsychological interventions.

A developmental increase in allostatic load from ages 3 to 11 years is associated with increased schizotypal personality at age 23 years

Although allostatic load has been investigated in mood and anxiety disorders, no prior study has investigated developmental change in allostatic load as a precursor to schizotypal personality. This study employed a multilevel developmental framework to examine whether the development of increased allostatic load, as indicated by impaired sympathetic nervous system habituation from ages 3 to 11 years, predisposes to schizotypal personality at age 23 years. Electrodermal activity to six aversive tones was recorded in 995 subjects at age 3 years and again at 11 years. Habituation slopes at both ages were used to create groups who showed a developmental increase in habituation (decreased allostatic load), and those who showed a developmental decrease in habituation (increased allostatic load). Children who showed a developmental increase in allostatic load from ages 3 to 11 years had higher levels of schizotypal personality at 23 years. A breakdown of total schizotypy scores demonstrated specificity of findings to cognitive-perceptual features of schizotypy. Findings are the first to document a developmental abnormality in allostasis in relation to adult schizotypal personality. The relative failure to develop normal habituation to repeated stressors throughout childhood is hypothesized to result in an accumulation of allostatic load and consequently increased positive symptom schizotypy in adulthood.

An evaluation of analytical approaches for understanding change in cognition in the context of aging and health

OBJECTIVES

In this article, we discuss the importance of studying the relationship between health and cognitive function, and some of the methods with which this relationship has been studied.

METHODS

We consider the challenges involved, in particular operationalization of the health construct and causal inference in the context of observational data. We contrast the approaches taken, and review the questions addressed: whether health and cognition are associated, whether changes in health are associated with changes in cognition, and the degree of interdependency among their respective trajectories.

RESULTS

A variety of approaches for understanding the association between cognition and health in aging individuals have been used. Much of the literature on cognitive change and health has relied on methods that are based at least in part on the reorganization of between-person differences (e.g., cross-lag analysis) rather than relying more fully on analysis of within-person change and joint analysis of individual differences in within-person change in cognition and health.

DISCUSSION

We make the case for focusing on the interdependency between within-person changes in health and cognition and suggest methods that would support this.

Validity of urinary monoamine assay sales under the "spot baseline urinary neurotransmitter testing marketing model"

Spot baseline urinary monoamine assays have been used in medicine for over 50 years as a screening test for monoamine-secreting tumors, such as pheochromocytoma and carcinoid syndrome. In these disease states, when the result of a spot baseline monoamine assay is above the specific value set by the laboratory, it is an indication to obtain a 24-hour urine sample to make a definitive diagnosis. There are no defined applications where spot baseline urinary monoamine assays can be used to diagnose disease or other states directly. No peer-reviewed published original research exists which demonstrates that these assays are valid in the treatment of individual patients in the clinical setting. Since 2001, urinary monoamine assay sales have been promoted for numerous applications under the "spot baseline urinary neurotransmitter testing marketing model". There is no published peer-reviewed original research that defines the scientific foundation upon which the claims for these assays are made. On the contrary, several articles have been published that discredit various aspects of the model. To fill the void, this manuscript is a comprehensive review of the scientific foundation and claims put forth by laboratories selling urinary monoamine assays under the spot baseline urinary neurotransmitter testing marketing model.

A transdisciplinary perspective of chronic stress in relation to psychopathology throughout life span development

The allostatic load (AL) model represents an interdisciplinary approach to comprehensively conceptualize and quantify chronic stress in relation to pathologies throughout the life cycle. This article first reviews the AL model, followed by interactions among early adversity, genetics, environmental toxins, as well as distinctions among sex, gender, and sex hormones as integral antecedents of AL. We next explore perspectives on severe mental illness, dementia, and caregiving as unique human models of AL that merit future investigations in the field of developmental psychopathology. A complimenting transdisciplinary perspective is applied throughout, whereby we argue that the AL model goes beyond traditional stress–disease theories toward the advancement of person-centered research and practice that promote not only physical health but also mental health.

Stressors over the life course and neuroendocrine system dysregulation in Costa Rica

OBJECTIVE

A key aspect of the increasingly popular allostatic load (AL) framework is that stressors experienced over the entire life course result in physiological dysregulation. Although core to AL theory, this idea has been little tested, and where it has been tested, the results have been mixed.

METHOD

The study analyzes the Costa Rican Study on Longevity and Healthy Aging (CRELES), a new, cross-sectional, and nationally representative survey of older Costa Rican men and women (aged between 60 and 109 years). The survey period is between 2004 and 2006, and the survey has a sample size of 2,827 individuals. This article focuses on the relationship between a variety of stressors experienced over the life course and cortisol, dehydroepiandrosterone sulfate (DHEAS), epinephrine, and norepinephrine analyzed separately and in an index.

RESULTS

There are some links between certain stressors and worse cortisol levels, but overall, almost all of the stressors examined are not associated with riskier neuroendocrine biomarker profiles.

DISCUSSION

More work is needed, in order to establish the connection between stressors experienced over the life course and resting levels of the neuroendocrine markers.

Age-related memory impairments due to reduced blood glucose responses to epinephrine

Increases in blood glucose levels are an important component of the mechanisms by which epinephrine enhances memory formation. The present experiments addressed the hypothesis that a dysfunction in the blood glucose response to circulating epinephrine contributes to age-related memory impairments. Doses of epinephrine and glucagon that significantly increased blood glucose levels in young adult rats were far less effective at doing so in 2-year-old rats. In young rats, epinephrine and glucose were about equally effective in enhancing memory and in prolonging post-training release of acetylcholine in the hippocampus. However, glucose was more effective than epinephrine in enhancing both memory and acetylcholine release in aged rats. These results suggest that an uncoupling between circulating epinephrine and glucose levels in old rats may lead to an age-related reduction in the provision of glucose to the brain during training. This in turn may contribute to age-related changes in memory and neural plasticity.

Biomarkers related to aging in human populations

Biomarkers are increasingly employed in empirical studies of human populations to understand physiological processes that change with age, diseases whose onset appears linked to age, and the aging process itself. In this chapter, we describe some of the most commonly used biomarkers in population aging research, including their collection, associations with other markers, and relationships to health outcomes. We discuss biomarkers of the cardiovascular system, metabolic processes, inflammation, activity in the hypothalamic-pituitary axis (HPA) and sympathetic nervous system (SNS), and organ functioning (including kidney, lung, and heart). In addition, we note that markers of functioning of the central nervous system and genetic markers are now becoming part of population measurement. Where possible, we detail interrelationships between these markers by providing correlations between high risk levels of each marker from three population-based surveys: the National Health and Nutrition Examination Survey (NHANES) III, NHANES 1999-2002, and the MacArthur Study of Successful Aging. NHANES III is used instead of NHANES 1999-2002 when specific markers of interest are available only in NHANES III and when we examine the relationship of biomarkers to mortality which is only known for NHANES III. We also describe summary measures combining biomarkers across systems. Finally, we examine associations between individual markers and mortality and provide information about biomarkers of growing interest for future research in population aging and health.

Rethinking gender differences in health: why we need to integrate social and biological perspectives

The complexity of gender differences in health (i.e., men's lower life expectancy and women's greater morbidity) extends beyond notions of either social or biological disadvantage. Gaps remain in understanding the antecedents of such differences and the issues this paradox raises regarding the connections between social and biological processes. Our goals in this analytic essay are to make the case that gender differences in health matter and that understanding these differences requires an explanation of why rational people are not effective in making health a priority in their everyday lives. We describe some salient gender health differences in cardiovascular disease, immune function and disorders, and depression and indicate why neither social nor biological perspectives alone are sufficient to account for them. We consider the limitations of current models of socioeconomic and racial/ethnic health disparities to explain the puzzling gender differences in health. Finally, we discuss constrained choice, a key issue that is missing in the current understanding of these gender differences, and call on the social science community to work with biomedical researchers on the interdisciplinary work required to address the paradoxical differences in men's and women's health.