How Much B12 is Enough?

Source: Tufts University
October 11, 2002 (Reviewed: October 19, 2004)

Vitamin B12 deficiency is a health issue for many older adults, with multiple factors, including poor diet, atrophic gastritis, reduced intestinal absorption, and drug interactions contributing to the problem. While clinicians recognize the need for B12 supplementation in these at-risk individuals, it's not clear how much extra B12 is enough to provide a 'safety net' to otherwise healthy older adults.

Addressing this issue, a study published in the Journal of the American Geriatrics Society demonstrated that the regular use of non-prescription vitamin supplements (which typically contain 2 to 25 micrograms of B12) was enough to maintain adequate B12 stores in a group of healthy seniors.

Measurement of B12 status

Canadian researchers polled 242 healthy men and women aged 65 and older on their use of dietary supplements that contained B12; they also reported on their medications, usual diet, and medical history. The Mini-Mental State Examination (MMSE) was used to screen out those with signs of cognitive dysfunction or depression. Blood tests determined serum levels of B12, as well as methylmalonic acid (MMA), methylcitric acid (MCTR), and homocysteine (HYCS), all metabolites know to be affected by B12 status.

Effect of dietary supplements

Of the 242 participants, 37 (15%) had serum B12 levels below normal range (165 pmol/L); most of these people were not taking B12 supplements. Only about 25% of the group was taking supplements, all of which provided between 2.6 and 37.5 micrograms B12. But even at this relatively low dose, supplement use in this population provided significant protection against low B12 levels (p<0.005). Results showed a dose dependent relationship between oral vitamin dose and B12 status, and an inverse relationship between B12 dose and MMA (p=0.005), HCYS (p=0.05), and MCTR (p=0.05).

Advice to patients

B12 deficiency leads to cognitive and behavioral changes that are slow to develop and, at first, hard to detect. The resulting neurological damage, however, can't be reversed. The people in this study who did not use supplements were more likely than supplement users to have elevated levels of metabolites, an 'early warning' sign that had gone unrecognized in this apparently healthy group of people.

Generic multivitamins sold in the US include at least the RDA of 2.4 micrograms B12, but specialized 'senior formulas' often supply appreciably more than that. Current US nutrition guidelines advise older adults to regularly consume B12-fortified foods or to take a multivitamin that includes B12.

Source

• Is low-dose oral cobalamin enough to normalize cobalamin function in older people? A. Garcia, A. Paris-Pombo, L. Evans,  et al., J Amer Geriatr Soc, 2002, vol. 50, pp. 1401--1404

Related Links
B12 Screening an Essential Part of Seniors' Health Care
Vitamin Shortfall Linked to Alzheimer's Disease
Vitamin Therapy May Cut Cost of Heart Disease
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