The cobalamins are a group of cobalt containing B vitamins (cyanocobalamin, methylcobalamin and adenosylcobalamin) that are collectively called vitamin B12. Vitamin B12 is required as a cofactor for methionine synthase, an enzyme that converts homocysteine to methionine using tetrahydrofolate (THF) as a methyl donor. High homocysteine levels are a risk factor for cardiovascular disease, and research has shown that folate and vitamin B12 are able to lower elevated plasma levels. The elderly can be particularly vulnerable to B vitamin deficiencies because vitamin B absorption declines with age and energy intakes fall. Synergism occurs between folate and vitamin B12, whereby without vitamin B12, the methyl group from N5-methyl-THF can not be removed. Thus regeneration of THF does not occur. This physiological situation is called the methyl-folate trap and the reduced levels of THF result in inhibited synthesis of rapidly proliferating cells that require THF.
Researchers1 have investigated the vitamin B12, folate and homocysteine plasma levels of ≈5600 Canadian individuals aged between 6 and 79 years in order to assess the effects of folate fortification in foods since 1998. The data collected was part of the Canadian Health Measures Survey during 2007 to 2009, and included data that measured serum vitamin B12, red blood cell folate and plasma total homocysteine. Interestingly, 4.6% of the Canadians sampled were clinically vitamin B12 deficient (<148pmol/L, mean value 309pmol/L), although there was no evidence of folate deficiencies. There was a higher incidence of vitamin B12 deficiency amongst obese individuals compared to normal weight individuals, which might suggest that B12 is sequestered in fat tissue, thus reducing plasma levels. The authors reported that 5.1% of Canadians in the survey had elevated homocysteine, and these individuals were more likely to be vitamin B12 deficient, and have lower folate status.
These results support previous studies showing an inverse association between some B vitamins and homocysteine levels. The elderly were more likely to have poor vitamin B status compared to the young, something that has been previously reported. The 5% of individuals with high homocysteine levels were also more likely to have lower vitamin B12 status. An association that has already been found for vitamin B6, which is also required for homocysteine removal, albeit via a different enzyme (cystathionine β-synthase). Associations between vitamin B12 and folate intakes have been reported, and the likely reason for this is that they are often present together in supplements. It would therefore be expected that those individuals with the highest intakes would likely be those who supplement the vitamins in combination. Based on current research, these individuals have the lowest risk of elevated homocysteine levels.
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