Two blood proteins linked to future disability in adults 85+

In a Japanese aging study, 230 adults aged 85–89 began without disability. About 4.5 years later, two signals in their blood stood out: higher levels of beta-2-microglobulin, or B2M, and cystatin C were associated with a greater likelihood of losing functional independence. The work was led by Yusuke Osawa and Yasumichi Arai at Keio University, with Luigi Ferrucci of the U.S. National Institute on Aging.

The team used machine learning and statistical analysis to screen 29 plasma proteins. Each increase in B2M was associated with a disability hazard ratio of 1.35; for cystatin C, the hazard ratio was 1.42. Those associations held after the researchers accounted for age, sex, kidney function, lifestyle factors and other possible confounders. A hazard ratio describes how the likelihood of an event changes in the study group; it does not by itself prove that one factor causes the other.

The result did not stay confined to Japan. In the Italian Invecchiare in Chianti, or InCHIANTI, aging study, which followed participants for up to 15 years, elevated B2M and cystatin C were again associated with greater disability risk, especially among people aged 80 years and older. Other proteins initially linked with mortality were not replicated, making the disability signal for these two proteins the study’s most consistent finding.

The biology offers a clue. Both proteins are associated with kidney function, while B2M also reflects chronic low-grade inflammation, sometimes called “inflammaging.” The researchers suggest that these processes may accompany the gradual decline in physical function, but the study does not establish that either protein directly causes disability.

And so, concretely? Because B2M and cystatin C can already be measured with standard clinical assays, they could eventually help clinicians identify very old adults who might benefit from earlier exercise, nutritional support or rehabilitation. For now, they remain promising risk markers: the cohorts show an association, not that blood testing improves independence, and no preventive intervention was tested in this study.