By Debra Wein, MS, RD
The Facts About Vitamin B12
itamin B12, often thought of as strictly a concern for complete vegetarians, is being investigated further. In fact, recent research indicates that meat eaters and people with depression may also have limited B12 stores. According to the Dietary Reference Intakes released by the National Academy of Sciences in 1999, adults should take in 2.4 micrograms per day (mcg/day) of vitamin B12--an increase from the 2.0 mcg/day Recommended Dietary Allowance (RDA) stipulated in 1989. The report also suggests older adults might best obtain the necessary levels of B12 from fortified foods and supplements. The report states: "Because 10 to 30 percent of older people may malabsorb food-bound B12, it is advisable for those older than 50 years to meet their RDA mainly by consuming foods fortified with B12 or a supplement containing B12." In addition, further research recently published in the American Journal of Clinical Nutrition (Tucker et al. 2000) indicates that people under 50 might also benefit from taking in B12 from fortified food and supplements.
V I T A M I N B 12 P L A S M A CONCENTRATIONS
New research suggests that people with vitamin B12 plasma concentrations below 258 picomoles per liter (pmol/L) could be deficient in the vitamin. In the past, only those patients with levels below 148 pmol/L were diagnosed as clinically deficient.
STATUS CONCENTRATION (PMOL/L)
Normal Low to normal Clinically deficient
> 258 148-258 <148
What Is the Best Vitamin Source? A recent review (Tucker et al. 2000) of nearly 3,000 subjects (1,564 women and 1,435 men), ages 26 to 83 (984 subjects 26-49; 1,460 subjects 50-64; 555 subjects 65 and above) compared subjects' vitamin B12 plasma concentrations with sources of vitamin B12 ingested. Researchers used three values to assess B12 stores: less than 148 picomoles per liter (pmol/L) signifies a clinical deficiency; less than 258 pmol/L means a deficiency risk exits, though further testing is needed; and less than 185 pmol/L was the researcher's midpoint. In this study, 16 percent of the
subjects had plasma levels below 185 pmol/L; 39 percent had plasma levels below 258 pmol/L, putting them at risk for deficiency; and 8 percent were clinically deficient in vitamin B12, with levels below 148 pmol/L. After analyzing the subjects' diets, researchers came to the following conclusions: I Subjects who did not use supplements but consumed fortified cereal more than four times per week were half as likely to have low B12 concentrations as subjects who consumed neither supplements nor cereal. In fact, the 41 percent of subjects who did not take supplements or eat fortified cereal had the highest prevalence of low vitamin B12 concentrations (less than 185 pmol/L). I The group in the highest tertile of vitamin B12 intake from meat, poultry and/or fish took in approximately three times as much B12 as the group in the lowest tertile of vitamin B12 intake from this source. However, the vitamin B12 plasma concentrations of subjects in the highest tertile of meat consumption compared to those in the lowest did not reflect this difference. And compared to the cereal and milk groups, vitamin B12 plasma concentrations in the meat group were significantly lower, despite similar average vitamin B12 intake in these three groups.
The relationship between plasma concentrations and dairy intake of vitamin B12 was similar to the relationship between plasma concentration and cereal intake, rather than meat intake. Subjects in all food intake groups were significantly more likely to have lower vitamin B12 plasma concentrations (less than 185 pmol/L) than subjects in the supplement group. Twenty-eight percent of the subjects took supplements containing B12. Of the subjects taking supplements, only 8 percent had low vitamin B12 concentrations (less than 185 pmol/L) compared to 20 percent of subjects who did not take supplements.
The Bottom Line Cereal eaters were significantly less likely to have low plasma B12 concentrations than those who did not eat cereal. A positive relationship between plasma concentrations and intake appeared strongest for cereal and supplements and weaker for other foods, including meat, fish and poultry. This relationship existed even after adjusting for age, sex, body mass index, smoking, alcohol use and total calorie intake. Researchers believe that the protective effect of supplements, cereal or both may have been due to two factors. First, consuming these sources of vitamin B12 may have increased subjects' total intake of the vitamin. Plasma concentrations increase along with vitamin B12 intake until intake nears 10mcg/day, when the curve appears to level. The second possible factor is that the form of vitamin B12 in supplements, cereals and perhaps dairy foods may be more bioavailable than the form of B12 in other foods. Cooking meat, fish and poultry subjects the vitamin to heat degradation and loss (Tucker et al. 2000).
IDEA PERSONAL TRAINER
Vitamin B12 and Depression Consuming appropriate levels of vitamin B12 may help maintain mental as well as physical health, according to new research reported in the American Journal of Psychiatry (Penninx et al. 2000). In this study, physically disabled women 65 years and older with a vitamin B12 deficiency were twice as likely to be severely depressed as those not deficient in B12. Of the 700 study participants, 68.3 percent were not depressed, 14.3 percent were mildly depressed and 17.4 percent were severely depressed. The subjects' average age was 77.3 years. Similar to the Tucker study, cutoffs for potential vitamin B12 deficiency were 258 pmol/L and 148 pmol/L. Of the severely depressed women, 40.2 percent had vitamin B12 levels below the 258 pmol/L cutoff--significantly higher than the 31.6 percent among the nondepressed subjects. Similarly, 9.8 percent of the severely depressed subjects had vitamin B12 levels below the lower 148 pmol/L cutoff compared to 6.1 percent of the nondepressed subjects. Researchers hypothesized that a relationship between low B12 concentration and increased risk of depression exists because vitamin B12 is involved with reactions related to brain function. It should be noted that this was a cross-sectional study, which looked at
more than 700 subjects. The results cannot strictly confirm a cause-andeffect relationship between depression and vitamin B12 concentration. Also, since the results apply to disabled women only, further studies should examine both sexes as well as people who are not disabled. However, researchers believe the relationship is significant. Debra Wein, MS, RD, is president of The Sensible Nutrition Connection Inc., and an adjunct faculty member at Simmons College, The Boston Conservatory and the University of Massachusetts. Register at SensibleNutrition.com to receive her free e-mail newsletter, SNaC Bytes.
© 2001 by IDEA Health & Fitness Inc. All rights reserved. Reproduction without permission is strictly prohibited.