When we use the word “age” in common speech, we are usually referring to our chronological age, or the number of years since our birth. When medical researchers talk about “aging,” they usually refer to processes of biological maturation or decline that occurs over time. Of course, these two ideas of aging are not identical—individuals biologically develop very differently. However, cognitive decline research indicates that chronological age is still the most frequently used proxy for biological change across time. This is mostly a result of our limited understanding of the biological mechanisms of cognitive aging.
A recent study in the Journals of Gerontology reveals how specific biomarkers (specifically measurable biological characteristics) relate to cognitive aging independently of chronological time. This supports the theory that cognitive decline in later life is better understood by looking at specific physical health factors rather than chronological age. The researchers used data from the Victoria Longitudinal Study, a Canadian sample of adults between 55 and 85 years of age. Biological and cognitive data were collected from VLS participants at multiple points over a period of about six years.
The researchers analyzed participants’ scores on five different cognitive measures, as well as four biomarkers that previous research has linked to cognitive decline: grip strength, lung function, blood pressure, and Body Mass Index. In their statistical analysis, the researchers first established that each of the cognitive and biological markers showed change over time. In a second step, the researchers examined how each cognitive and biological marker changed together. In other words, they examined whether a higher-than-average change in any biomarker was associated with a similarly high change in cognitive scores. Thus, the researchers were testing whether or not any of these biomarkers were predictive of cognitive change.
The study found that each of the biomarkers had some association with some form of cognitive decline, independent of time. While each association was fairly modest, the fact that each biomarker had a time-independent relationship with cognition adds to our understanding of biological age. This may lead to improved detection and intervention strategies against cognitive decline, as well as expand our theoretical understanding of biological aging.
MacDonald, S.W.S., DeCarlo, C.A., and Dixon, R.A. (2011). “Linking Biological and Cognitive Aging: Toward Improving Characterizations of Developmental Time.” The Journals of Gerontology Series B: Psychological Sciences and Social Sciences, 66B (S1).