Long-term memory correlates negatively with plasma transcobalamin in healthy elderly with normal plasma cobalamin levels

Plasma Vitamin B-12 Levels and Risk of Alzheimer’s Disease: A Case-Control Study

Introduction: Vitamin B-12 deficiency is a frequent condition in the elderly population. High homocysteine levels, which can contribute to arterial damage and blood clots in blood vessels, usually indicate a deficiency in vitamin B-12. Different studies have shown an association of raised total homocysteine with incident Alzheimer’s disease. This study aimed to evaluate the association between vitamin B-12 levels and the risk of Alzheimer’s disease (AD). Methods: A case-control study with a sample size of 90 was conducted at Tertiary hospital, Kathmandu. The participants who visited the psychiatric outpatient department from 2019 onward at Tertiary hospital, Kathmandu, were recruited. The Mini-Mental State Examination (MMSE) was administered to the participants by a trained medical doctor. The medical doctor used the MMSE scores to classify the participants into two groups: the healthy control group and the AD group. Results: The AD group had higher percentages of hypertension (20.9%), diabetes (13.6%), smoking habit (27.3%), vitamin B-12 deficiency (22.7%), and alcohol consumption (13.8%) relative to the control group. Among these features, a significant association was found between alcohol and vitamin B-12 status and between systolic blood pressure and MMSE score. Conclusion: This study concluded that there is an association between low levels of vitamin B-12 and the risk of AD. Further studies are needed to determine the cause-effect.

Plasma total homocysteine and memory in the elderly: the Hordaland Homocysteine Study

We examined the relation between plasma total homocysteine (tHcy), folate, vitamin B12, and episodic memory in elderly community-dwelling subjects. A population-based study was conducted in 1992 and 1993, and subjects were re-investigated after 6 years. Plasma analytes were determined on both occasions. At follow-up, memory performance, using the Kendrick Object Learning Test, was investigated in 2,189 subjects (age, 65-67 years at baseline). Subjects with memory deficit (test score, < 25) had higher tHcy and lower folate at follow-up compared with those without memory deficit: 12.6 (95% confidence interval [CI], 12.1, 13.1) versus 11.5 (95% CI, 11.3, 11.6) micromol/L (p < 0.001) for tHcy, and 6.7 (95% CI, 6.2, 7.1) versus 7.6 (95% CI, 7.5, 7.8) nmol/L (p < 0.001) for folate. The risk of memory deficit increased according to quintiles of tHcy both at baseline and at follow-up. A decline in tHcy, or an increase in folate, over a 6-year period was associated with a higher memory test score; and vice versa. These findings indicate that increased plasma tHcy is an independent risk factor for memory deficit both cross-sectionally and prospectively, and that a "favorable" change in folate or tHcy concentrations over time is associated with better memory performance.

Holotranscobalamin and Total Transcobalamin in Human Plasma: Determination, Determinants, and Reference Values in Healthy Adults

Background: We developed microbiological assays (MBAs) to identify determinants and to establish reference values for cobalamin bound to transcobalamin [holotranscobalamin (holoTC)] and total TC in plasma.

Methods: We captured holoTC with magnetic beads with TC antibodies and used a conventional MBA for cobalamin measurements. Total TC was determined as holoTC after TC was saturated with cyanocobalamin. The new assays were compared with published methods. Determinants and reference values were determined in 500 blood donors, ages 18–69 years.

Results: Determination of cobalamin, holoTC, and TC by MBA required &lt;150 μL. HoloTC and TC by MBA correlated with holoTC by RIA (r = 0.95) and TC by ELISA (r = 0.79), respectively. Between-day CVs for holoTC and total TC were 4%–9%. Women had lower holoTC than men, but only at age ≤45 years. In multivariate regression analyses, holoTC was positively associated with age (in women only), creatinine (in men only), and plasma concentrations of total TC, folate, and cysteine, but inversely correlated with homocysteine and methylmalonic acid. For all study participants, total TC was associated with holoTC and number of TCN2 766C alleles; in female participants only, total TC was also associated with age, homocysteine, and cysteine. Reference values were 670–1270 pmol/L for TC and 42–157 pmol/L for holoTC, but they differed according to age and sex.

Conclusions: Our MBAs for TC and holoTC required low plasma volume and performed acceptably compared with other methods. Determinants of holoTC and TC differed between men and women and according to age. Separate reference intervals for holoTC should be considered in younger women.