Although we all age, the rate and extent of our aging varies greatly and is somewhat disconnected from our chronological age. Some individuals are vigorous and healthy well into their 90s while others experience failing health decades earlier. To account for these differences, scientists introduced the concept of biological age. Biological age describes molecular and biochemical changes that are more reflective of our true aging rate than is our chronological age. Our individual genetics plays an important role in biological aging, but environmental influences and our personal lifestyle choices also can be major contributors to how fast or slow we age. Epigenetic changes (see Can Aging Be Reversed blog from 9/10/19) are one factor that has been shown to correlate with biological aging. A major ongoing effort in science is to define other markers that reflect biological age so that eventually personalized reports can be generated for an individual. More importantly, the hope is that understanding these markers may provide ways to improve longevity and reduce early mortality.
A new publication in Nature Medicine dives deeply into the marker search by following 106 individuals ranging in age from 29-75 years old (median age 55.74 years). Subjects were assessed over 4 years with repeated visits and extensive sampling of molecular, biochemical, and clinical indicators. In total, the researchers collected more than 18 million data points on these individuals and used statistical analysis to identify correlations with age. From this analysis, 184 markers were found that correlated with age, some increasing with age and some decreasing. Diet, physical activity, and medication usage didn’t change significantly in the overall group during this 4-year study, so these three factors did not appear to account for the aging correlations. Interestingly, the correlations at the group level didn’t always occur at the individual level. For example, a marker that generally increased with age might actually decrease with age in certain people. The observation that individuals don’t all follow the population trends highlights the need for very individualized analysis for clinical evaluation.
Examining the distribution of the 184 markers into biological pathways, the authors found four major overlapping pathways of aging that they termed ageotypes: 1) immune function 2) metabolic function 3) liver function and 4) kidney function. Individuals varied greatly in their ageotypes from persons low in markers for all four ageotypes to persons high in markers for all four types. However, markers reflecting immune dysfunction and inflammation were particularly correlated with aging. Another interesting observation was that two subjects who lost weight during the study improved in many of their aging markers. These two findings are consistent with other studies showing that lifestyle interventions, such as weight loss or reducing inflammation through diet or medication, appear to reduce biological aging. Still, the large diversity of ageotype patterns across the spectrum of individuals tested again reflects the need for much more study and very personalized analysis before any specific clinical recommendations can be made.