Scientists may be getting closer to developing a blood test for depression, according to a new study that looked at how certain immune cells age inside the body.
The research suggests that changes in these cells may be linked to emotional and thinking-related symptoms of depression rather than physical symptoms such as tiredness or sleep problems.
The findings were published in The Journals of Gerontology, Series A: Biological Sciences and Medical Sciences.
Depression is one of the most common mental health conditions in the world. In the United States alone, nearly one in five adults experiences depression at some point in life. The condition can affect emotions, thinking, relationships, work, sleep, appetite, and overall health.
Despite how common depression is, doctors still do not have a simple laboratory test that can confirm the condition. Today, depression is mainly diagnosed through conversations between patients and healthcare professionals. Doctors ask about symptoms, emotions, behavior changes, sleep, appetite, and mood over time.
This approach can work well, but depression is also highly complex because symptoms vary greatly between people. Some individuals mainly experience physical symptoms such as fatigue, low energy, changes in appetite, or restlessness.
Others mostly struggle with emotional and cognitive symptoms such as hopelessness, difficulty concentrating, lack of motivation, or anhedonia, which is the inability to feel pleasure from activities that once felt enjoyable.
Researchers say this variety makes depression difficult to measure objectively.
The new study was led by Nicole Beaulieu Perez, assistant professor at NYU Rory Meyers College of Nursing. Her team wanted to investigate whether biological signs in the blood could help explain some forms of depression more clearly.
The researchers focused on biological aging, which refers to how old the body appears at a cellular level rather than a person’s actual age in years.
Scientists can now estimate biological age using tools called epigenetic clocks. These tools examine chemical changes that happen to DNA over time. Some people may have cells that appear biologically older than expected, which may reflect stress, illness, inflammation, or other health problems.
The study involved 440 women, including 261 women living with HIV and 179 women without HIV. Depression symptoms were measured using a standard questionnaire called the Center for Epidemiologic Studies Depression Scale.
The researchers also collected blood samples and analyzed biological aging in immune cells.
One important focus was monocytes, a type of white blood cell involved in immune defense and inflammation. Monocytes are especially important in HIV because the infection can strongly affect the immune system. Previous studies have also linked inflammation and immune changes to depression.
The researchers discovered that faster aging in monocytes was strongly connected to emotional and cognitive symptoms of depression. These included hopelessness, feelings of failure, and loss of pleasure or motivation.
Interestingly, the aging markers were not strongly linked to physical symptoms such as fatigue.
This finding surprised researchers because physical symptoms are often more noticeable in people living with chronic illnesses such as HIV. Scientists say the results suggest that immune cell aging may be tied more closely to mood and mental processing than previously understood.
The study also compared two different types of epigenetic clocks. One measured aging across many different cell types throughout the body, while the other focused specifically on monocytes.
Only the monocyte-based measurements showed strong links to depression symptoms.
Researchers believe this may help explain why broad biological measurements sometimes fail to detect mental health conditions accurately. Specific immune cells may provide clearer clues than general aging markers.
The findings could eventually help doctors detect depression earlier and more objectively. Scientists also hope biological testing may one day help personalize treatment by predicting which medications or therapies may work best for different patients.
At the same time, the researchers emphasized that this work is still in an early stage. The study does not mean doctors can currently diagnose depression using a blood test.
More research will be needed to confirm the findings in larger and more diverse groups of people. Scientists also want to better understand whether immune cell aging directly contributes to depression or simply reflects other biological changes happening in the body.
Looking carefully at the study, the findings appear important because they connect mental health symptoms with measurable biological changes rather than relying entirely on self-reported experiences.
The study also focused on emotional and cognitive symptoms specifically, which may help improve understanding of different forms of depression. However, the research cannot yet prove cause and effect, and the findings are still too early for direct clinical use.
Even so, the results support growing evidence that mental health conditions involve both the brain and the immune system, opening the possibility that future depression diagnosis and treatment may become more personalized and biologically informed.
Source: NYU Rory Meyers College of Nursing.
