There will always be a debate within our general population that aging is only based on a chronological number. Once you are over a certain number life must be seen as ending. Never to be a functional human ever again. This is so very wrong! Very little awareness exists regarding anyone’s biological age (BA). Our chronological (CA) age isn’t set in stone!
For many aging is a complicated process characterized by progressive decline in physical, mental and reproductive capacities, leading to a loss of function, increased susceptibility to disease, and ultimately the end of life. The goals should be about prevention on what is commonly assumed.
At this time, the world is facing increasing life expectancy and population aging trends. It is important to increase our understanding on the mechanism of aging and improve the quality of the lives for people. Life expectancy shows considerable variation among individuals with equal or similar CAs due to diversity in genotypes and in living habits and environments.
A 50-year-old individual may have a 60-year-old body functions, and many people look older or younger compared to others at the same CA (including twins). Therefore, CA is not an optimal indicator for the aging progress.
Considering the lack of a golden index for aging, researchers have established various statistical models based on cognitive age, physical fitness age, biological age (BA). The degree of frailty predicts susceptibility to adverse outcomes independently of chronological age.
According to a report by the World Health Organization (WHO), the global population aged 65 and over is projected to double to 1.5 billion between 2029 adn 2050, with one in six people being aged 65 or over.
There is an enormous amount of research on how and why people age the way they do. While the rapid global increase in lifespan is striking, the health span, also known as a disease-free lifespan, has not increased at the same pace. The global burden of disease is increasing dramatically due to high rates of age-related functional decline, non-communicable chronic disease, and mortality.
In 2010, there were 777 million years lived with disability from all causes, up from 583 in 1990. Age-related disorders, including cancer, cardiovascular disease, and neurodegenerative disease contributed to over 30% of the disabled. This is a life threatening concept to adults. Both chronological and biological age.
And yet, there is a large variation in health outcomes among people of the same chronological age. At the individual level, different cells, tissues, and organs exhibit different aging trajectories.
BIOMARKERS OF AGING
Chronological age poorly reflects internal biological processes and individual variation. Researchers have shifted their focus to biological markers of aging. The concept of “a biomarker of aging” was firstly introduced in 1988 by Sprott et al., described as a biological parameter of an organism to predict functional capability.
Biological age can be indicated by the interactions between cellular and biochemical processes, leading to a individual -specific reflection on physiological function and overall health.
The American Federation for Aging Research developed criteria for aging biomarkers based on Johnson and Butler et al, research. According to their guidelines, a biomarker of age needs (1) better performance for predicting age and age-associated outcomes. (2) monitor the aging process in systems rather than effects of the disease. (3) have the ability to be repeatedly tested in a harmless way, both in humans and animals. At these requirements are too strict that few biomarkers could fulfill, currently there are no gold standard criteria or methods established for developing aging biomarkers.
Molecular and Cellular Aging Biomarkers
Telomere length – Telomeres are at the ends of chromosomes which can protect DNA from damage and instability. In most cells of this type, telomeres will shorten 50-150 base pairs after every cell cycle. Telomere length is considered as a marker of aging considering most human somatic cells will undergo a limited number of divisions until the protective function of telomers is exhausted, leaving cells vulnerable to mutations. Growing evidence also demonstrates a strong correlation between age and telomere shortening.
Telomere length has proved itself to be a promising aging biomarker and was significantly associated with frailty and functional decline of the lung, heart and kidney.
Participants with Type 2 diabetes mellitus, coronary heart disease, lung cancer, lymphocytic leukemia, and lymphoma generally exhibited shorter cellular telomere length compared to that of control groups. A large number of cohort studies have consistently reported an association between telomere length and mortality risk.
Shortening of leukocyte telomere length is also associated with the incidence and progression of age-related disease, including CVS, neuropsychiatric disorders, diabetes, and multiple cancers (e.g. gastrointestinal, head and neck cancers).
Ongoing research is focusing on refining its measurement and interpretation, which may ultimately promote the reliability of telomere length as an aging biomarker.
Omics Biomarkers
The term “omics” refers to the high dimensional analysis of whole molecular biology. The concepts of omics started with the study of genes, as DNA was the first discovered biological macromolecule.
Currently, omics can interpret near-entire biologic data from organisms including the study of supporting structure of genome including modifications on DNA, the study of all RNA types, the study of small molecules, microbiotics (the study of genes and genomes of microbiota).
Epigenetics
DNA methylation is an advanced chemical modification system, where depending on its activation or inhibition, can alter genomes of different cell types and development processes.
DNA methylation is the most studied epigenetics trait to estimate biological age in the last decade. In 2013, the epigenetic clock was proposed by researchers Hannum et. al. based on whole blood from full age range samples.
Data from participants with age-related diseases have established the concept of epigenetic age acceleration (EAA). In African Americans, EAA was significantly associated with CVD risk factors, such as systolic blood pressure and fasting glucose. In terms of functional markers, it was found that people with greater EAA had poorer performance on lung function, walking speed, grip strength, cognitive ability, verbal fluency, selective attention task, and frailty.
EAA is not only associated with risk of cancer but also the prognosis of cancer, independent of chronological age and traditional CVD risk factors, greater EAA was a promising predictor for incident fatal coronary heart disease, peripheral arterial disease, heart failure, and ischemic stroke outcomes.
Moreover, EAA was associated with higher risk for incident CVD events, and a predictor for dementia, Alzheimer’s Disease, Parkinson’s Disease, and posttraumatic stress disorder. EAA is also documented to be associated with changes in frailty over time.
Inflammatory Profiles
Inflammation is a defense mechanism mediated by inflammatory proteins in response to perceived noxious stimuli. With the broad deregulation of functioning immune cells with aging, accumulating evidence indicates that inflammatory molecules moderately rise, touted as “inflammaging.” Most older individuals have numerous elevated proinflammatory markers (termed the senescence-associated secretory phenotype or SASP) like C-reactive protein (CRP). CRP is a blood test that most doctors can order.
These SASP would modify the tissue microenvironment and alter the function of nearby normal cells. A prolonged and persisting inflammation will result in the accumulation of tissue damage, ultimately leading to age-related pathologies.
Sayed et al. proposed an inflammatory aging clock from 50 circulating markers of inflammation, including cytokines and growth factors, all of which highly correlated with chronological age.
Inflammation is known to lead to many diseases.
Interventions aimed at slowing the aging process and extending a healthy life span are equivalent to preventive interventions for a positive biological age gap.
If you would like to learn more about other biomarkers of aging, Please read the article titled Biomarkers of ageing: Current state-of-the-art, challenges, and opportunities.” Authors are Ruiye Chen, et al. Found through Google Scholars.
