Low Vitamin B12 Linked to Smaller Brains and Cognitive Decline

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Brian Hagiwara

Older people may not be getting enough vitamin B12, and that could affect their thinking and the size of their brain, according to a new study.

For the research published in the journal Neurology, scientists led by Christine Tangney, an associate professor of clinical nutrition at Rush University Medical Center, followed a group of 121 people aged 65 or older for 4.5 years. The researchers measured the participants’ blood levels of vitamin B12 and markers of its breakdown products. They also recorded people’s performance on tests of thinking skills and took MRI scans of their brains.

The researchers found that low levels of vitamin B12 were linked to smaller brain volumes and lower scores on cognitive tests. Vitamin B12 is critical for normal red blood cell formation, as well as for producing other agents important for maintaining healthy DNA, hormones, proteins and fats the body needs.

Because experts have disagreed over whether B12 levels in the blood accurately reflect how much of the vitamin the body is actually using, the researchers also looked for compounds that build up when there isn’t enough B12 and when body processes that rely on the vitamin don’t occur. These compounds include homocysteine and methylmalonic acid (MMA). Indeed, as homocysteine and MMA levels increased among the volunteers in the study, their scores on tests measuring global cognition, memory and perception dropped.

“Almost all of the markers of B12 deficiency are strongly and inversely related to cognitive function, which means that as they rise, there was lower brain volume and worse performance on the cognitive tests,” says Tangney.

Tangney started investigating the effect of vitamin B12 levels on cognition when an earlier study she conducted found that MMA levels among the elderly were relatively high. MMA, she says, is a better indicator of B12 status since it picks up how much B12 is actually absorbed by the tissues. Since MMA works with B12 to produce another important metabolite, buildup of MMA is a sign that there isn’t enough B12 around for the process to take place.

Vitamin B12 deficiency is particularly concerning among the elderly, since people tend to absorb less of the vitamin already with age. Anywhere from 1.5% to 15% of the adult U.S. population may be deficient in vitamin B12, according to the latest health statistics. The most recent Dietary Reference Intakes developed by the Institute of Medicine currently recommend at least 2.4 micrograms (mcg) of vitamin B12 daily (a 3-oz. serving of salmon contains nearly 5 mcg of B12, while a cereal fortified with 100% of the daily value for B12 contains 6 mcg).

Other foods high in vitamin B12 include fish, meat (especially liver), poultry, eggs, milk, and milk products.

Vitamin B12 gaps are also a potential problem among the growing number of American patients with diabetics who take metformin. The popular medication to treat Type 2 diabetes interferes with B12 absorption.

For the current study, a team of neurologists, nurses and neuropsychological technicians conducted an in-depth series of 17 brain function tests on the elderly volunteers in their homes, including evaluations of word list recall, logical memory, delayed recall, number ordering and naming and reading skills. The MRI scans were done on participants who agreed to the procedure, and were done only once for each person. That means that Tangney’s team couldn’t track changes in brain volume in individual participants across time, but could only compare brain volume in those with low and high levels of B12 intake.

Based on her findings, Tangney says she would recommend that more American adults take B12 supplements, since the vitamin is so crucial to brain function, especially as people age. Testing for B12 deficiency, she says, might also be a good way to help many seniors avoid age-related cognitive problems and possibly help them maintain their intellectual vigor.

If deficiencies are discovered, people can start taking B12 supplements or get shots of the vitamin, which may hold off or even reverse decline in cognitive functions. “If we can do something simple for patients before they need big tests of their cognitive function, that’s important and potentially useful,” Tangney says.

Alice Park is a writer at TIME. Find her on Twitter at @aliceparkny. You can also continue the discussion on TIME‘s Facebook page and on Twitter at @TIME.