White blood cells called neutrophils are the body’s first line of defense against infection. When the immune system is active, the number of neutrophils can rise quickly, changing the balance with other immune cells.
Doctors can see this balance with a simple number called the neutrophil‑to‑lymphocyte ratio (NLR). The ratio comes from a standard complete blood count, a test most people get when a doctor checks for infection.
New research from NYU Langone Health shows that this easy‑to‑get number might also warn us about future Alzheimer’s disease. The scientists looked at NLR results from almost 400,000 patients in two large health systems.
Large Study Connects Immune Balance to Dementia Risk
The study, published online on April 3 in Alzheimer’s & Dementia, used data from about 285,000 patients at four NYU Langone hospitals and roughly 85,000 veterans from the VA health system.
Researchers chose each person’s first qualifying NLR reading after age 55, making sure the test happened before any dementia diagnosis. They then followed the patients to see who later developed Alzheimer’s or other dementias.
Higher NLR Means Higher Risk
Across both groups, people with a higher NLR were more likely to develop dementia, both in the short term and over many years. “High” meant a value above the median – half the participants were above it, half below.
The link was strongest in Hispanic patients and in women, suggesting that genetics or access to care might influence the result.
Why This Blood Marker Matters
Dr. Ramos‑Cejudo explains that a single high NLR cannot diagnose Alzheimer’s, but it can add useful information when combined with other risk factors. It could help doctors decide who needs closer monitoring or early testing.
Do Neutrophils Help Drive the Disease?
Neutrophils protect us from infection, but they can also cause damage when they become overactive. In Alzheimer’s, they may harm blood vessels and brain tissue. Animal studies have shown that neutrophils can speed up disease progression.
As we age, the body’s ability to clear old neutrophils changes, which might increase tissue injury. However, scientists have not yet proven that neutrophils directly cause dementia.
Ongoing Work
Dr. Ramos‑Cejudo’s team is studying whether neutrophils actively contribute to cognitive decline. They are pairing blood‑cell measurements with advanced brain scans (PET and diffusion MRI) and mental‑function tests.
“If neutrophils turn out to be more than a marker, they could become a new target for treatment,” he says. “Meanwhile, the NLR could be a first step toward earlier detection and intervention.”
Funding
The project was funded by several National Institutes of Health grants, the National Alzheimer’s Coordinating Center, the VA Boston Healthcare System, the Alzheimer’s Association, and the BrightFocus Foundation.