# Longitudinal Trends and Analytical Consistency of Folate and Vitamin B12 Biomarkers: Two Decades of Population-Based Data and Diagnostic Implications

## TL;DR

This study analyzed 20 years of blood data to track changes in vitamin B12 and folate levels, finding stable B12 but rising folate levels, with implications for nutrition and lab testing.

## Contribution

The study provides longitudinal population-based data on vitamin B12 and folate biomarkers and evaluates the impact of a diagnostic platform transition.

## Key findings

- Median vitamin B12 levels remained stable from 2005 to 2024.
- Folate levels increased from 10.5 to 15.5 nmol/L over the same period.
- The 2021 lab platform change caused measurable shifts in folate measurements.

## Abstract

Background/Objectives: Vitamin B12 (cobalamin) and folate (vitamin B9) are essential cofactors in one-carbon metabolism required for DNA synthesis, methylation, and genomic stability. Deficiencies in these nutrients can cause megaloblastic anemia, neurological dysfunction, and hyperhomocysteinemia, linking micronutrient imbalance to cardiovascular and neurocognitive outcomes. Population-based surveillance of these biomarkers provides insight into nutritional trends and supports analytical standardization. Methods: This retrospective study included all routine plasma (P) vitamin B12 and folate measurements performed at Uppsala University Hospital from 2005 to 2024 (n = 647,302 and 578,509, respectively). Data were extracted from the laboratory information system and summarized using annual medians, percentile distributions, and coefficients of variation (CV). Linear regression was used to validate the method comparison and assess the impact of the 2021 transition from the Abbott Architect to the Roche cobas platform. Descriptive statistics summarized the temporal and seasonal patterns of P-vitamin B12 and P-folate. Results: Median P-vitamin B12 concentrations remained stable (340–370 pmol/L; median CV = 4.6%), while P-folate increased from 10.5 to 15.5 nmol/L (median CV = 12.9%) from 2005 to 2024. Low P-folate (<7 nmol/L) was observed in 7.1% of measurements and low or borderline P-vitamin B12 (<250 pmol/L) in 22.6%. Females exhibited slightly higher concentrations of both analytes. Although no clear seasonal pattern was observed, small biological effects cannot be excluded. Sample volumes decreased during the summer. The transition to Roche assays introduced measurable methodological shifts, particularly for P-folate. Conclusions: Levels of P-vitamin B12 remained stable over two decades, while P-folate status increased modestly. This reflects both dietary influences and assay-related differences following the 2021 platform transition. Continuous surveillance of biomarker medians provides a sensitive tool for detecting analytical drift and for monitoring long-term nutritional trends in clinical populations.