Advocating for More Careful Use of the Term "Biological Age"
People age at different rates, and any give population will distribute across a range of late life health status and mortality risk. As a concept, biological age is clearly useful, a way to talk about this variance in pace of aging. The output of an attempt to measure biological age is not biological age, however. It is a measure that may or may not reflect biological age. Some researchers feel that current use of the term "biological age" is lax, often applied without qualification to the output of epigenetic clocks and other assessments.
Usage of the phrase "biological age" has picked up considerably since the advent of aging clocks and it has become commonplace to describe an aging clock's output as biological age. In contrast to this labeling, biological age is also often depicted as a more abstract concept that helps explain how individuals are aging internally, externally, and functionally. Given that the bulk of molecular aging is tissue-specific and aging itself is a remarkably complex, multifarious process, it is unsurprising that most surveyed scientists agree that aging cannot be quantified via a single metric.
We share this sentiment and argue that, just like it would not be reasonable to assume that an individual with an ideal grip strength, VO2 max, or any other aging biomarker is biologically young, we should be careful not to conflate an aging clock with whole-body biological aging.
To address this, we recommend that researchers describe the output of an aging clock based on the type of input data used or the name of the clock itself. Epigenetic aging clocks produce epigenetic age, transcriptomic aging clocks produce transcriptomic age, and so forth. If a clock has a unique name, the name of the clock can double as the output. As a compromise solution, aging biomarkers can be described as indicators of biological age. We feel that these recommendations will help scientists and the public differentiate between aging biomarkers and the much more elusive concept of biological age.
Apparently a rant becomes a study if you add charts and citations. I of course agree in general. It has now become commonplace for media outlets to use the phase biological age in their clickbait stories. This recent one is particularly cringe because she is only 33: "Kayla Barnes-Lentz, 33, says she has reduced her biological age by a decade - now she's sharing her secrets so others can do the same"