Around 74% of Americans with Alzheimer’s disease, a type of dementia, are ages 75 years or older, according to the Alzheimer’s Association. The condition can also develop in people under 65 years of age. This is known as younger-onset or early onset dementia.
Being able to detect signs of dementia as early as possible and screen for the possible risk may help to improve treatment outcomes or slow down the progression of the disease.
Medical News Today looks at its coverage of 4 recent studies on detecting Alzheimer’s disease early via means other than brain scans — one blood test based on changes in the gut microbiome, and another three based on the proteins tau and beta-amyloid and their variants.
A study published in The Lancet in May 2026 examined the feasibility of blood-based biomarker tests to detect early signs of cognitive decline in adults between the ages of 53 and 69 without a dementia diagnosis.
The study researchers focused on data from around 1,300 participants of the U.S. Coronary Artery Risk Development in Young Adults (CARDIA) Study.
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Among the participants, around 6% had high blood levels of proteins tau and beta-amyloid. Five years later, the same individuals experienced greater cognitive decline compared with those who did not have high levels of beta-amyloid and tau.
In a previous interview with Medical News Today, Megan Glenn, PsyD, clinical neuropsychologist in the Center for Memory and Healthy Aging at the Hackensack Meridian Neuroscience Institute at Jersey Shore University Medical Center in New Jersey, who was not involved in this study, said:
“We have known for a long time that subtle cognitive changes and biological markers, particularly amyloid accumulation, begin developing decades before a patient meets the criteria for a formal dementia diagnosis.”
“We have been searching for accessible ways to detect these earliest signs during this ‘preclinical’ phase so we can intervene sooner, and this study represents a major step toward making early detection scalable and accessible to the general public,” she said.
A cohort study of 2,766 older women, published in JAMA Network Open in March 2026, found that the protein plasma phosphorylated tau 217 (pTau217) may help predict signs of dementia up to 25 years before symptoms appear.
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At the start of the study, participants had no memory or cognitive problems. Ranging from 1 to 25 years later, those who had higher levels of pTau217 — of which there were 1,311 participants — had experienced mild cognitive decline or dementia.
The study noted some association between higher pTau217 levels, dementia, and factors such as age and genetics. For example, those carrying the APOE ε4 gene and individuals older than 70 years experienced a more significant cognitive decline.
While such biomarkers may help predict dementia years before symptoms appear, further research is necessary.
Ebrahim Zandi, Ph.D., associate professor of immunology and immune therapeutics at the University of Southern California, who was not involved in the study, commented on the study’s limitations in a previous interview with MNT.
“The cohort consisted exclusively of older postmenopausal women, limiting applicability to men or younger populations,” he said.
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“Although the study examined racial subgroups and effect modification, sample sizes in minority groups were smaller, and APOE data were not uniformly available across all groups. This raises important questions about biomarker thresholds and performance across diverse populations,” he added.
In a study published in Nature Communications in April 2026, researchers found that the pTau217 biomarker may help detect signs of cognitive decline earlier than tests such as PET scans can. Brain scans are traditionally used to help diagnose dementia.
For an average of 8 years, the study followed 317 adults ages between 50 and 90 years who did not have any thinking or memory problems at the start of the study.
Those with higher levels of pTau217 at the start of the study experienced faster cognitive decline. The study noted that higher pTau217 levels were linked with a greater accumulation of the amyloid-beta protein, the buildup of which experts believe may be the main cause of Alzheimer’s disease.
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Discussing the blood tests in a previous interview with MNT, lead study author Hyun-Sik Yang explained:
“There are already 2 FDA-approved pTau217 blood tests in clinical use. As more data accumulate, blood tests — especially pTau217 — appear to be as good as, or even better than, cerebrospinal fluid testing and show excellent concordance with amyloid-β PET.”
Researchers from the University of East Anglia in the United Kingdom studied the relationship between Alzheimer’s disease and microbe-derived metabolites (MDMs), waste products produced by gut bacteria, publishing their results in Gut Microbes.
The study involved analyzing blood and stool samples of 15 adults ages 50 years and older. Some participants had no signs of cognitive impairment, while others had mild cognitive impairment or subjective (self-reported) cognitive impairment.
The researchers used machine learning to examine the 33 metabolites they identified in the samples. They found lower levels of key neuroprotective metabolites, which support brain health, in people with mild or subjective cognitive impairment.
The same individuals also had elevated levels of a cytotoxic metabolite, indoxyl sulfate, suggesting that lower levels of neuroprotective metabolites or higher levels of cytotoxic metabolites may indicate cognitive decline.
In a previous interview with MNT, Dung Trinh, MD, an internist with MemorialCare Medical Group and the chief medical officer of the Healthy Brain Clinic in Irvine, CA, who was not involved in the study, spoke about these findings.
“[The study] suggests that a small panel of blood metabolites linked to diet and the gut microbiome may help identify people with very early cognitive changes, which is exciting because we need less invasive ways to detect risk sooner,” he said.
“At the same time, this was a relatively small, cross-sectional study, so it shows association rather than proving that these markers can reliably predict who will go on to develop dementia,” he added.
