Understanding the long-term temporal relationship between body mass index (BMI) trajectories and Alzheimer’s disease (AD) pathologies is critical for identifying preclinical risk. Researchers recently characterized the stage-specific BMI dynamics that precede a Mild Cognitive Impairment (MCI)/AD diagnosis. The results clarify the complex association between BMI and Alzheimer’s disease, showing a clear bidirectional link at different stages of the illness. Furthermore, this work sheds light on the “obesity paradox” seen in late-life AD studies.
Amyloid Precedes Decline
The longitudinal cohort study analyzed 1570 participants from the Alzheimer’s Disease Neuroimaging Initiative (ADNI). Initial findings suggest a causal link between AD pathology and subsequent BMI changes. Specifically, frontotemporal β-amyloid (Aβ) deposition, an early marker of AD, preceded and predicted a decline in preclinical BMI. This finding supports the hypothesis that AD pathophysiology, which begins years before cognitive symptoms, disrupts weight control mechanisms in the brain. Therefore, weight loss may start one to two decades before the expected onset of symptoms in individuals with autosomal dominant AD (ADAD).
In contrast, low BMI and accelerated weight loss in later life have an established association with an increased risk of AD. The recent analysis further revealed that the observed preclinical BMI decline correlated with accelerated neurodegeneration, including hypometabolism, during the subsequent transition to MCI. Moreover, this trajectory of decline is particularly notable among individuals who later receive an MCI or dementia diagnosis.
Bidirectional Relationship Between BMI and Alzheimer’s
The association between BMI and Alzheimer’s disease is time-dependent. Obesity in midlife is a well-known risk factor for developing future AD. However, a higher BMI in late life often correlates with a reduced risk of AD, a phenomenon called the “obesity paradox.” Because of this, it is plausible that BMI acts both as a risk factor and as a prodromal sign of dementia, depending on when the measurement occurs. Consequently, monitoring and managing BMI changes over time offer important implications for identifying and preventing cognitive impairment in older adults.
Therefore, the new study supports a two-way pathway. First, the AD pathology (Aβ accumulation) drives weight loss in the preclinical phase. Second, the subsequent low BMI and associated physiological changes accelerate neurodegeneration and cognitive decline. This complex trajectory highlights the need for clinicians to monitor BMI changes as a critical biomarker for disease progression. Additionally, this insight may prompt intervention strategies targeted at weight stabilization and nutritional status during the very early stages of AD.
Frequently Asked Questions
Q1: What is the primary temporal finding regarding BMI decline and AD pathology?
The study found that frontotemporal β-amyloid (Aβ) deposition, an early marker of Alzheimer’s disease, precedes and predicts a subsequent decline in Body Mass Index (BMI) during the preclinical stage of the disease.
Q2: How does the BMI decline relate to the progression of Alzheimer’s disease?
The preclinical decline in BMI correlates with accelerated neurodegeneration, specifically hypometabolism, during the transition phase from being cognitively unimpaired to developing Mild Cognitive Impairment (MCI).
Q3: Why is the relationship between BMI and AD referred to as the “obesity paradox”?
The relationship is paradoxical because a high BMI in midlife increases the risk of AD, yet a low or rapidly declining BMI in late life is a sign of underlying preclinical AD pathology and is associated with increased risk.
References
- Dang M et al. Stage-specific temporal associations between body mass index trajectories and Alzheimer’s disease pathologies. Eur Radiol. 2026 Jan 28. doi: 10.1007/s00330-025-12258-w. PMID: 41603947.
- Raffi A et al. Decreased body mass index in the preclinical stage of autosomal dominant Alzheimer’s disease. Alzheimers Dement. 2017 Apr;13(4):427-434.
- Morris MC et al. Body Mass Index Trajectories Preceding Incident Mild Cognitive Impairment and Dementia. JAMA Netw Open. 2022 Oct 3;5(10):e2236113.
- Rajan KB et al. Change in cognition and body mass index in relation to preclinical dementia. Alzheimers Dement (Amst). 2016 Oct 18;5:87-93.
- Dhana K et al. Body Mass Index and Polygenic Risk for Alzheimer’s Disease Predict Conversion to Alzheimer’s Disease. J Gerontol A Biol Sci Med Sci. 2020 Jan 1;75(1):146-152.