Researchers call for raising RDA for vitamin B12; wild salmon seen as superior source
by Craig Weatherby
Some people's brains shrink as they approach or enter their elder years.
And, unsurprisingly, age-related brain shrinkage is associated with the development of dementia.
Now, the results of a British study show that people with higher blood levels of vitamin B12 are six times less likely to experience brain shrinkage—a change associated with development of dementia—compared to people with lower B12 levels.
Prior studies have linked B12 deficiency to pernicious anemia, cardiovascular disease, cancer, and neurodegenerative disorders.
Lower B12 levels have been associated with cognitive impairment, probably because B12 helps maintain healthy nerve cells, form red blood cells, and synthesize DNA.
But as many as one-quarter of the elderly have mild B12 deficiency. Vegetarians who avoid all animal products are also at risk of B12 deficiency.
Link found between low B12 levels and brain shrinkage
Scientists from the University of Oxford followed 107 volunteers aged 61 to 87, none of whom were vitamin B12 deficient (Vogiatzoglou A et al. 2008).
Blood samples were taken to measure levels of vitamin B12, homocysteine, and folate (another B vitamin linked to dementia and atherosclerosis).
The blood was also tested for levels of compounds called holotranscobalamin (holoTC) and methylmalonic acid (MMA), which serve as markers for absorption of dietary B12.
Annual brain shrinkage among the volunteers was calculated using MRI scans.
Over a five-year period, the researchers noted greater brain shrinkage among people with lower vitamin B12 and holoTC levels.
In fact, the volunteers with the lowest blood levels of B12 were six times more likely to experience brain shrinkage.
(Neither high homocysteine levels nor low folate levels were linked to brain shrinkage.)
As the researchers wrote, “Low vitamin B12 status should be further investigated as a modifiable cause of brain atrophy and of likely subsequent cognitive impairment in the elderly” (Vogiatzoglou A et al. 2008).
Earlier study linked higher B12 levels to dementia deterrence
Last year, researchers from the University of Oxford followed 1,648 volunteers for 10 years.
They reported that the participants with higher vitamin B12 blood levels were 30 percent less likely to develop age-related cognitive decline (ARCD) or other forms of dementia.
The British team also found that increased levels of the amino acid homocysteine—a known risk factor for atherosclerosis (plaque-ridden arteries)—doubled the risk of dementia or cognitive impairment.
Previous epidemiological studies link high levels of homocysteine with suspected or confirmed dementia, and homocysteine levels can be lowered by higher intake of vitamin B12 and folate.
These findings dovetail with those from the new report, which linked higher vitamin B12 levels to reduced risk of brain shrinkage in older people.
They suggest that it may be wise to test older individuals annually for B vitamin levels.
And they reinforce the wisdom of eating balanced diets rich in brain-friendly B vitamins, omega-3s, and antioxidants.
Rise in B12 intake urged; wild salmon are superior sources
The current vitamin B12 recommended daily allowance (RDA) for people aged 14 or older is 2.4 micrograms (mcg).
But absorption can vary among people, so it is wise to exceed the RDA substantially, as insurance.
At-risk groups such as the elderly and vegans should take supplemental vitamin B12.
The U.S. Institute of Medicine (IOM) has not established an upper limit for vitamin B12 because, as the IOM states, “…no adverse effects have been associated with excess vitamin B12 intake from food and supplements in healthy individuals.”
The IOM recommends that adults older than 50 years take vitamin B12 supplements, because of the high rate of impaired absorption of vitamin B12 from animal foods.
Two years ago, Danish researchers examined the associations between vitamin B12 intake and markers of vitamin B12 deficiency in 98 postmenopausal women aged 41 to 75.
Their results show that RDA levels for vitamin B12 should be raised to 6 mcg (Bor MV et al. 2006).
Wild salmon are superior sources of B12, providing from 4 to 7 mcg of vitamin B12 per 3.5 oz serving (USDA Nutrient Database), compared with only 2 mcg in beef.
And wild salmon also provide abundant amounts of omega-3s, high intakes of which are associated with reduced rates of dementia.
- Bor MV, Lydeking-Olsen E, Møller J, Nexø E. A daily intake of approximately 6 microg vitamin B-12 appears to saturate all the vitamin B-12-related variables in Danish postmenopausal women. Am J Clin Nutr. 2006 Jan;83(1):52-8.
- Clarke R, Birks J, Nexo E, Ueland PM, Schneede J, Scott J, Molloy A, Evans JG. Low vitamin B-12 status and risk of cognitive decline in older adults. Am J Clin Nutr. 2007 Nov;86(5):1384-91.
- Feng L, Ng TP, Chuah L, Niti M, Kua EH. Homocysteine, folate, and vitamin B-12 and cognitive performance in older Chinese adults: findings from the Singapore Longitudinal Ageing Study. Am J Clin Nutr. 2006 Dec;84(6):1506-12.
- McCracken C, Hudson P, Ellis R, McCaddon A; Medical Research Council Cognitive Function and Ageing Study. Methylmalonic acid and cognitive function in the Medical Research Council Cognitive Function and Ageing Study. Am J Clin Nutr. 2006 Dec;84(6):1406-11.
- Vogiatzoglou A, Refsum H, Johnston C, Smith SM, Bradley KM, de Jager C, Budge MM, Smith AD. Vitamin B12 status and rate of brain volume loss in community-dwelling elderly. Neurology. 2008 Sep 9;71(11):826-32.
- von Castel-Roberts KM, Morkbak AL, Nexo E, Edgemon CA, Maneval DR, Shuster JJ, Valentine JF, Kauwell GP, Bailey LB. Holo-transcobalamin is an indicator of vitamin B-12 absorption in healthy adults with adequate vitamin B-12 status. Am J Clin Nutr. 2007 Apr;85(4):1057-61.