1000mcg Oral Vitamin B12 do not Bring Low Plasma Levels Back to Normal

You probably take a multivitamin, do you? Well, you eat healthy, as well? But does this mean you get enough of all nutrients? Maybe... maybe not. In a recent study (Baer. 2011) on vitamin B12 deficiency and supplementation in healthy young women, of the 300 participants, 137, i.e. 46%, had low-normal plasma levels of vitamin B12.

Interestingly, in participants with very low B12 levels, neither supplementation with 1000mcg of oral methylcobalamin, nor the consumption of a cereal meal (probably a bad idea, anyway) 4x/week for three months was able to restore B12 to an acceptable level:

Supplementation of either vitamin B12 pill or 100% RDA fortified cereal for 3 consecutive months resulted in significant (p < 0.05) increase in mean plasma vitamin B12 levels in all subjects (Table 4). Subjects whose baseline plasma vitamin B12 status was < 200 pg/ml were not observed to increase plasma vitamin B12 levels to at or above the 250 pg/ml benchmark following three months supplementation by either pills or 100% fortified cereal.

The scientists also have an answer as to why this might have been the case - malabsorption:

Upwards of 40% of all subjects who demonstrated plasma vitamin B12 values at or below the low-normal range reported daily use of medications associated with adversely affecting vitamin B12 absorption—significantly higher than the number of subjects who were observed to have plasma vitamin B12 levels above 250 pg/ml.

Bear & Parker's advice to people, especially from this "high-risk" group, is thus to supplement with "a higher dose of supplemental vitamin B12 (oral pill form) or sublingual methylcobalamin or IM methylcobalamin" in order to sufficiently correct vitamin B12 status.