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C O M P L E T E T I T L E : How Does Subjective Age Get “Under the Skin”? The Association Between Biomarkers and Feeling Older or Younger Than One’s Age: The Health and Retirement Study.
F U L L T E X T S O U R C E : Innovation in Aging_Oxford Academic
Abstract
Background and Objectives
Though subjective age is a well-recognized risk factor for several chronic diseases, the biological basis for these associations remains poorly understood.
Research Design and Methods
We used new comprehensive biomarker data from the 2016 wave of the nationally representative Health and Retirement Study (HRS) to evaluate the association between biomarker levels and self-reported subjective age in a subset of 3,740 HRS participants who provided a blood sample. We measured biomarkers in seven biological domains associated with aging: inflammation, glycemia, lipids, liver function, endocrine function, renal function, and cardiac function. The primary outcome was the age discrepancy score (subjective age − chronological age) categorized as those who felt younger, older, or the same as their chronological age (reference group). Analyses adjusted for comprehensive psychosocial factors (chronic stress index, depression score), demographic factors (race, sex, body mass index, marital status, physical activity), and prevalence of chronic health conditions (comorbidity index).
Results
The prevalence of clinically relevant reduced levels of albumin concentrations was lower in those who felt younger (8.8% vs. 16.0%; p = .006) and higher in those who felt older (20.4% vs. 16.0%; p = .03) when compared with the reference category. The prevalence of clinically significant elevation in liver enzymes such as alanine aminotransferase was also significantly lower among those who felt younger (7.1% vs. 8.6%; p = .04) when compared with the reference category. Prevalence of clinically elevated levels in cystatin C was also lower among those who felt younger when compared with the reference category (50.0% vs. 59.1%; p = .04). There was no association between lipids, glucose, or C-reactive protein (inflammatory marker) and subjective age categories.
Discussion and Implications
These results suggest that people who feel younger may have favorable biomarker profiles and as a result may have lower prevalence of age-related diseases when compared with those who feel older or those who feel the same as their chronological age.
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With the unprecedented growth and increasing life expectancy in individuals 65 or older, the U.S. Office of Disease Prevention’s Healthy People plan, HealthyPeople 2020, has prioritized healthy aging; yet, more than 60% of older adults manage two or more chronic conditions (1, 2). Chronological age remains one of the most potent risk factors for a variety of chronic diseases, though there is wide variability in disease prevalence among people of the same chronological age. Hence, investigators have evaluated whether certain psychosocial and biological aspects of aging may moderate the effects of chronological age on various diseases.
Researchers have defined biological age (3) as an alternate summary measure that better reflects overall physiological function when compared with chronological age. A second construct related to aging that has emerged in the psychosocial literature is subjective age, which evaluates an individual’s self-evaluation of how old one perceives oneself to be (4). Though subjective age is a multidimensional construct that includes how old one feels (felt age), how old one would like to be (desired age), and at what age old age begins (perceived age), subjective age is commonly studied as a unidimensional construct with the first construct (felt age) being most extensively studied with regards to health outcomes (5–9). There are two theoretical frameworks to explain why subjective age is associated with a variety of adverse health outcomes including mortality; a social and psychological perspective that views subjective age as being associated with social and environmental cues such as social roles and loneliness (10) and a biomedical perspective that views subjective age as a proxy for individual’s physical health and functioning (11).
In support of the biomedical perspective, prior research has demonstrated that feeling older than one’s chronological age (“older subjective age”) has been found to be associated with several negative health outcomes including increased hospitalization (8), cognitive impairment (5, 6), dementia (6, 7), and higher mortality (9). Furthermore, older subjective age has been associated with increased levels of specific biomarkers such as cystatin C and C-reactive protein (CRP) (12, 13). However, a comprehensive assessment of biological pathways associated with subjective age has not been performed. Hence, it remains unclear whether individuals feel older or younger compared with their chronological age because of their underlying diseases or whether subclinical alterations in biomarkers themselves may be associated with younger or older subjective age. We hypothesize that altered levels of biomarkers that predispose to age-related diseases or biomarkers that change with chronological age will also be associated with older subjective age.
To address this hypothesis, we utilized a novel data source—new comprehensive biomarker data linked with Health and Retirement Study (HRS) data—to assess the relationship between various biomarkers and subjective age. The HRS, a large nationally representative survey, measured large numbers of age-related biomarkers that can be categorized into two broad groups. The first group of biomarkers were those associated with age-related biological process, for example, CRP, which is a commonly used biomarker to estimate systemic inflammation which increases with age (14, 15), dehydroepiandrostenidione (DHEAS), a marker of endocrine function, that has shown to decrease with age (15), or albumin, a marker of nutritional status, that decreases with age (15). The second group of biomarkers were those that are risk factors for age-related diseases, for example, lipid levels that are well-established risk factors for cardiovascular disease (16) or are used to define age-related diseases, fasting glucose is used to identify individuals with diabetes, serum creatinine/cystatin C is used to identify individuals with chronic kidney disease and alterations in liver enzymes are used to diagnose liver dysfunction. The availability of detailed biomarker information along with self-reported prevalence of chronic diseases and a broad range of psychosocial variables in HRS makes this a unique data source to address whether there is an independent association between subjective age and biomarkers after adjustment for psychosocial factors and prevalent chronic diseases. This study will help address whether subjective age can be used as a surrogate for an individual’s physical health and be used to identify individuals at higher risk for age-related chronic diseases and provide further evidence to support the biomedical perspective of subjective age.
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Results
Table 1 shows sample demographic characteristics and biomarker levels by subjective age group. The average discrepancy score between subjective age and chronological age among those who felt younger (N = 2,802) was −14.79 years (SD: ± 9.22 years) and skewed left with a skewness of −1.59, whereas the discrepancy score for those who felt older (N = 402) was 7.46 ± 7.35 years skewed right with a skewness of 1.90. Most people (75%) felt younger than their chronological age, with 14% feeling the same, and another 11% feeling older than their chronological age. Hispanic/Latino adults were more likely to feel older when compared with their Black and non-Hispanic White counterparts. BMI and chronic stress were significantly higher among those who felt older when compared with those who felt younger. HDL-c and serum albumin were lower among those who felt older when compared with those in the reference category and higher in those who felt younger. In contrast, serum triglycerides were higher among those who felt older and lower among those who felt younger when compared with the reference category. The frequency of those who had 6–12 clinically elevated biomarkers was 18.12% among those who felt younger, 30.11% among those in the reference category, and 35.02% among those who felt older (p < .0001).
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