That finding, reported in Neurology, comes from researchers at Chicago's Rush University Medical Center. They found that older people with blood markers associated with vitamin B12 deficiency had the smallest brains and the lowest scores on tests measuring thinking, reasoning, and memory.
Though the new study doesn't prove that vitamin B12 deficiency caused those problems, older adults are more likely than younger people to have lower levels of vitamin B12, which is found in foods such as meat, fish, poultry, milk, eggs, and fortified breakfast cereals.
"As we get older our stomachs produce less of the acid that breaks down the vitamin to make it available for absorption," Rush University associate professor of clinical nutrition Christine Tangney, PhD, tells WebMD. "Older people also take more drugs that inhibit absorption, such as [the diabetes drug] metformin."
Vitamin B12 and Memory Loss
Low vitamin B12 levels, as indicated by higher levels of the amino acid homocysteine, was first linked to brain shrinkage in a 2008 study led by Oxford University emeritus professor of pharmacology A. David Smith.
Last year, the U.K. research team also reported findings from a small clinical trial showing that people who took supplements containing vitamin B12, vitamin B6, and folate had less brain shrinkage than people who did not take the supplements.
Earlier this month, the group reported that supplementation also appeared to slow cognitive declines in the same group of high-risk patients with early memory loss.
"We found that the vitamin B treatment not only slowed decline, it stopped it in some people with high levels of homocysteine," Smith tells WebMD.
The new study included 121 people aged 65 and older living on Chicago's south side. As part of a larger, ongoing aging and memory study, they underwent brain imaging an average of 4.5 years after taking memory and brain function tests.
They also got blood tests to check their vitamin B12 level and markers of vitamin B12 deficiency, including homocysteine and a substance called methylmalonate.
Low blood levels of B12 were not directly linked to poorer scores on the brain function tests or reductions in brain volume. But higher levels of the B12 deficiency markers, especially methylmalonate, clearly were, Tangney says.
She adds that measuring blood B12 levels is a notoriously poor indicator of vitamin insufficiency in older people.
"We saw much more rapid declines in memory in people who were deficient in B12 as assessed by these more sophisticated markers," Tangney tells WebMD.
Vitamin B12 Supplementation?
Brain imaging confirmed that higher levels of homocysteine and methylmalonate were associated with smaller brain size.
Tangney says it is too soon to recommend vitamin B12 supplementation as a strategy for slowing memory loss and brain shrinkage, even though the small U.K. study found that practice to be beneficial.
Smith agrees, but adds that elderly people with early evidence of memory impairment should have their homocysteine level checked. If levels are high, medically supervised vitamin B supplementation may be appropriate, he says.
He also recommends eating breakfast cereals fortified with vitamin B12.
"Ready-to-eat cereals are one of the best food sources of vitamin B12 for older people because the vitamin does get into the body," Tagney says.