Scientists Identify Blood Marker That Could Help Detect Depression Earlier

Researchers have identified a blood-based marker that may help detect depression earlier by tracking how specific immune cells age over time. The findings suggest that a simple test focused on monocytes, a type of white blood cell, could eventually complement traditional mental health assessments.

The study, published in The Journals of Gerontology, Series A, offers new insight into the biology of depression, which affects nearly one in five adults in the United States. Unlike current diagnostic approaches that rely heavily on self-reported symptoms, the new method points toward a potentially objective biological marker.

New clues from biological aging

Scientists investigated biological age using so-called epigenetic clocks — tools that estimate how quickly cells are aging based on chemical modifications to DNA. Biological age can differ sharply from chronological age, especially in people exposed to chronic illness, stress, or inflammation.

The study followed 440 women enrolled in the long-running Women’s Interagency HIV Study, including 261 women living with HIV and 179 without the virus. Participants completed detailed questionnaires about depression symptoms, while blood samples were analyzed for signs of accelerated cellular aging.

Researchers used two different epigenetic clocks: one designed to measure aging across multiple cell types and another focused specifically on monocytes. These immune cells play a central role in inflammatory responses and have repeatedly been linked to mental health changes associated with chronic inflammation.

Emotional symptoms showed the clearest connection

The team found that accelerated aging in monocytes was strongly associated with non-somatic symptoms of depression. These included anhedonia, feelings of hopelessness, and a sense of personal failure, both in women with HIV and those without it.

By contrast, monocyte aging showed little connection to physical symptoms such as fatigue, appetite changes, or sleep problems. Researchers note that these symptoms often overlap with HIV complications and other chronic illnesses, which can make depression especially difficult to identify in medically vulnerable groups.

Importantly, the broader epigenetic clock measuring whole-body cellular aging did not show a meaningful association with depression symptoms. This suggests that changes in specific immune cells — rather than generalized biological aging — may be more closely tied to mood and cognitive health.

Potential for earlier and more targeted care

Lead author Nicole Beaulieu Perez of NYU Rory Meyers College of Nursing said the findings highlight how depression can manifest differently between individuals. According to the researchers, focusing more closely on emotional and cognitive symptoms, rather than only physical complaints, may improve diagnosis accuracy, especially among patients with other health conditions.

For women living with HIV, depression is both common and medically significant, often interfering with adherence to antiretroviral therapy and worsening long-term health outcomes. A blood test capable of identifying early biological changes linked to depression could help clinicians intervene before symptoms become severe or begin affecting treatment adherence.

Still, experts caution that the findings remain preliminary and are far from routine clinical use. Larger and more diverse studies will be needed to confirm whether monocyte aging can reliably predict depression across broader populations and over longer periods of time.

Toward precision mental health

If future studies validate the findings, epigenetic testing could eventually become part of a more personalized approach to mental health care, combining subjective symptoms with measurable biological signals. Such tools could help identify individuals at greatest risk and guide more targeted treatment strategies.

Researchers also hope to better understand whether therapies aimed at reducing inflammation or slowing cellular aging could help ease depression symptoms. Previous studies have already linked chronic stress, immune dysfunction, and accelerated biological aging, but translating those findings into practical treatments remains a major challenge.

The study was supported by the National Institute of Mental Health and the National Institute on Minority Health and Health Disparities. The findings add to growing evidence that mental and physical health are deeply interconnected at the cellular level, reinforcing calls for more integrated approaches to healthcare.