B12 Levels Relate to Dietary Source in Framingham Study

Tucker KL et al. • Am J Clin Nutr

Key Finding

39% of adults have B12 levels below 350 pg/mL

Original title: “Plasma vitamin B-12 concentrations relate to intake source in the Framingham Offspring study”

Plain English Summary

Framingham Offspring Study analysis showing 39% of adults have B12 levels below 350 pg/mL, with plasma B12 strongly related to dietary intake source.

In-Depth Analysis

Background

Dr. Katherine L. Tucker and colleagues from the USDA Human Nutrition Research Center published this study in the American Journal of Clinical Nutrition (PMID: 10648266), examining B12 status in the Framingham Offspring cohort.

Study Design

Design: Cross-sectional analysis of Framingham Offspring Study Population: 2,999 adults aged 26-83 years Measurements: Plasma B12, dietary intake by food frequency questionnaire Analysis: B12 status by age group and dietary intake source

Key Findings

B12 status by level:

B12 Level (pg/mL)	Prevalence
<200	9%
200-350	30%
>350	61%

Total prevalence of low/marginal B12: 39% of adults

B12 by dietary source:

Source	Effect on B12
Fortified cereals	Strongest positive
Dairy	Positive
Meat	Modest positive
Supplements	Strong positive

Key finding: B12 from meat was less bioavailable than from fortified foods, especially in older adults.

Mechanistic Insights

Age-related decline in B12 status reflects:

•Gastric atrophy reducing intrinsic factor
•Reduced gastric acid (needed to release food-bound B12)
•Medications (PPIs, metformin) further impairing absorption
•Crystalline B12 (supplements, fortified foods) absorbed independently

Clinical Implications

39% of adults have suboptimal B12 status. Older adults may absorb supplemental B12 better than food-bound B12. Regular monitoring warranted, especially in elderly.

Metabolic Health Perspective

This Framingham data established population-level B12 insufficiency. For metabolic optimization, levels >500 pg/mL provide a margin of safety for neurological protection.