The following post was written by Cristina Marson, an undergraduate student studying Biomedical Sciences at the University of Oxford. The original post was slightly edited. We’d like to thank Cristina for this valuable voluntary contribution to highlight and summarise an important academic paper in our line of work.

Time is a universal concept and so all individuals age chronologically at the same rate. This is however not the case for biological aging. Several consequences arise from disparities between these two notions. The geroscience hypothesis depicts how accelerated biological aging is associated with an increased likelihood of developing certain diseases. Targeting this gradual deterioration in system integrity could be crucial for reducing one’s risk of developing age-related diseases.

The Dunedin Multidisciplinary Health and Development Research Study (often referred to as the Dunedin Study) is a longitudinal cohort study of 1037 people born in 1972-73 in Dunedin, New Zealand.

There’s already been separate publications using the data from this study, for instance Eleven Telomere, Epigenetic Clock, and Biomarker-Composite Quantifications of Biological Aging: Do They Measure the Same Thing? published in 2018 and using 38 years as a very early middle-age timepoint.

But now there is a definitive study out in Nature Aging showing Disparities in the pace of biological aging among midlife adults of the same chronological age have implications for future frailty risk and policy by Elliott et al. The post summarises this study for a general audience.

Elliott et al quantified two decades of biological aging in midlife by measuring changes in 19 biomarkers at ages 26, 32, 38 and 45. Biomarkers are key for identifying the severity of the aging process as it is clear that they can show a pattern of age-dependent decline in the functioning of multiple organ systems.

Examples of biomarkers included:

  • BMI
  • Blood pressure
  • Cardiorespiratory fitness
  • Lung capacity
  • Cholesterol
  • White blood cell count
  • Tooth decay

For example, the researchers monitored estimated glomerular filtration rate (eGFR) as an assessment of kidney function or determined the levels of inflammation in the blood by quantitatively measuring the levels of high sensitivity C-reactive protein. Overall, this wide range of measurements provided them with a broad assessment of the health of the participants’ cardiovascular, metabolic, renal, hepatic, pulmonary, immune, dental systems.

Although some biomarkers such as telomere length were not included due to the continued debate about how it is measured, the 2 decade follow-up of these biomarkers served to create an accurate representation of any progressive deterioration.

A ‘Pace of Aging’ score was calculated for each member of the study using 3 simple steps:

  1. Conversion of the biomarker value to a standardised scale (separate for men + women)
  2. Calculation of each study member’s personal slope for each of the 19 biomarkers
  3. Merging the 19 slopes to calculate an overall personal ‘Pace of Aging’ in order to a provide a quantitative determination of biological aging

Pace of Aging encompasses many of the individual differences observed in the rate of change within the integrity of multiple systems but what other factors were measured?

Assessing the biological age of a person’s brain using neuroimaging

Images of each participant’s brain were obtained using structural MRI and then used to analyse certain features including:

  • White matter vs grey matter volume
  • Hippocampal volume
  • Regional cortical thickness + surface area

An algorithm then combined this cortical anatomy information to provide a brain Age Gap Estimate (brainAGE) of the person’s brain. An older brainAGE predicts that the brain age of an individual is older than their chronological age and is therefore reflective of accelerated brain aging.

Assessing cognitive function

The Wechsler Adult Intelligence Scale-IV was used to test cognitive ability. It encompasses IQ together with 4 specific cognitive function domains: processing speed, working memory, perceptual reasoning and verbal comprehension.

A comparison of scores across the study was therefore a useful indicator of cognitive decline.

Using tests of functional fitness to assess sensorimotor functional capacity

  • Testing gait speed – time taken to walk a specified distance
  • One-legged balance
  • Grip strength
  • Vision test by measuring contrast sensitivity
  • Audiometry to measure hearing acuity

The use of surveys

A variety of surveys were used to assess the health of participants. Some surveys were completed by the participants themselves. Examples of these included:

  • Assessing physical limitations where participants were asked to assess their difficulty with completing various different activities
  • Assessing perceived longevity where individuals were asked questions such as ‘how likely is it that you will live to be 75 or more?’

Other studies went beyond self-reports and asked family or staff members to complete checklists or questionnaires in order to obtain a more accurate portrayal of the perceived health of an individual.

It is interesting to note the results obtained when considering attitudes towards aging. In particular, considering an individual’s negative perception of aging as it appears that older adults who self-report that they feel old are more likely to subsequently be diagnosed with an age-related disease.

Evaluation of this study

Results from this study show how huge disparities were observed in the biological aging of a population independent of chronological age. The findings raise the question of whether midlife is a window of opportunity for reducing the incidence of age-related disease. Interventions to slow the biological aging process may greatly improve the quality of life in older adults. This can also have wider social consequences in the future as it suggests how chronological age may not be the most useful indicator of health. If biological aging tests become more widely used, then biological aging measures could be utilised in the future when determining the allocation of healthcare and financial support.

Overall, this serves to highlight the growing importance of keeping track of your aging journey.  

Thanks for reading.

*Disclaimer: This information is for educational purposes only

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