Senescence varies substantially within and among populations. Data examined here extend knowledge on modern human variation by analyzing elders from Nagasaki Prefecture, Japan, enhance our understanding of relationships between senescence and human biology, and provide more information concerning the use of allostatic load (AL) as a measure of senescent decline among a non-Western population. Developing a valid method for assessing physiological variation due to senescence will benefit those studying health outcomes and survival of elders. It also will aid in focusing healthcare funds and interventions by targeting those most likely to experience unwanted outcomes. Understanding how Japan’s elders are surviving and adapting to old age, life-long stress, and developing dysfunction with increasing age provides a model of how others may slow senescence in other settings.
Background: 96 elderly residents of Sakiyama City, Nagasaki Prefecture (ages 55-89) and 27 elderly residents of Hizen-Oshima, Nagasaki Prefecture, Japan (ages 51-82) were sampled for components of allostatic load (AL) and other aspects of physical and physiological variation. Surveys were conducted by local health care nursing staff and members of a joint American-Japanese research team during participants’ yearly physical examinations. Japan was selected as the study site because Japanese men and women rank among the longest-lived people in the world and the population is relatively genetically homogenous.
Methods: AL is a summary measure of physiological activity across multiple regulatory systems pertinent to disease risks. AL incorporates data on ten components: systolic and diastolic blood pressure, high density lipoproteins, total cholesterol, glycosylated hemoglobin, dihydroepiandrosterone-sulfate, cortisol, noradrenaline, adrenaline, and waist:hip ratio. It is calculated by summing the number of components for which an individual’s values are in the highest risk quartile. Two alternate measures of AL were calculated for comparison. The first used decile as opposed to quartile cut-points. The second was constructed using principal components analysis (ALPC1). Multivariate regressions were used to analyze associations between AL, controlling for age and sex, and physiological variables in each sample.
Results: AL was higher among men than women and was poorly associated with age. Multivariate models of AL, sex, and age predict GTP, creatinine, white blood cell count, percent body fat, weight, dopamine, red blood cell count, GPT, and blood glucose variably by location. Associations between AL and physiological variables change when quartile vs. decile cut-points were used to construct the measure. ALPC1 showed significant associations in the Sakiyama sample with GPT, GTP, white blood cell count, creatine, dopamine, hematocrit, hemoglobin, red blood cell count, uric acid, and the self maintenance score of the Tokyo Metropolitan Institute of Gerontology Index of Competency.
Conclusions: The poor association between AL and age suggests AL may be assessing underlying senescence better than age alone. Higher AL indicates men in this sample experienced greater cumulative physiological and physical stress over their lives as compared to women in this Japanese setting. AL is significantly associated with immune, liver, and renal function, and aspects of frailty. These results provide additional support for suggesting AL measures physiological dysregulation and senescent decline across multiple somatic systems. Results from ALPC1 indicate sex is an important component in AL.