Plasma homocysteine as a risk factor for dementia and Alzheimer's disease.
Level 3 - non-randomized controlled study
Prospective cohort follow-up study analyzing incident dementia against baseline and historical biomarker levels
PubMed 11844848 · doi:10.1056/NEJMoa011613
What was done
A prospective cohort analysis evaluated 1,092 dementia-free participants (667 women and 425 men; mean age, 76 years) from the Framingham Study over a median follow-up of 8 years. Investigators examined the association between newly diagnosed dementia and plasma total homocysteine levels measured at baseline and 8 years prior. Multivariable proportional-hazards regression models adjusted for age, sex, apolipoprotein E genotype, vascular risk factors, and plasma concentrations of folate, vitamin B12, and vitamin B6.
What was found
Dementia developed in 111 participants, including 83 with Alzheimer's disease. Each 1-SD increase in log-transformed homocysteine was associated with a multivariable-adjusted relative risk of dementia of 1.4 (95% confidence interval, 1.1 to 1.9) for baseline or 8-year prior values. For Alzheimer's disease, the relative risk was 1.8 (95% CI, 1.3 to 2.5) per 1-SD increase at baseline and 1.6 (95% CI, 1.2 to 2.1) per 1-SD increase 8 years prior. A plasma homocysteine level exceeding 14 micromol per liter nearly doubled the risk of Alzheimer's disease.
Why it matters
This study demonstrates that elevated homocysteine precedes the clinical onset of dementia by years, indicating it is an independent prospective risk factor rather than solely a downstream consequence of nutritional deficiency in established dementia.
Limits
The observational design cannot establish whether homocysteine is causal or whether therapeutic homocysteine reduction lowers dementia incidence. The analysis was restricted to an older cohort (mean age 76) within a single community-based population, which may limit generalizability to other demographic groups.
Cited by
- supports A blood homocysteine level above 14 micromoles per liter increases the risk of developing dementia by 50%.