How B Vitamins Can Affect Brain and Heart Health

Eight essential nutrients make up the suite of B vitamins also known as the B complex. Research at Tufts and elsewhere has revealed that these B vitamins influence a vast spectrum of human health and disease, including cognitive function, cardiovascular health, gastric bypass recovery, neural tube defects, and even cancer.

“It’s hard to study the B vitamins in isolation,” says gastroenterologist Joel Mason, senior scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) and professor at the Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy and Tufts University School of Medicine. “Four of these B-vitamins cooperate as co-factors in many critical activities in cells in what we call ‘one carbon metabolism’.” 

One carbon metabolism is a series of pathways that allow for the transfer of single-carbon units to cells for essential processes such as DNA synthesis, amino acid metabolism, and more. It’s their role in all these crucial biological functions that make the B vitamins so important—and so challenging to tease out how they contribute positively and, perhaps negatively, to human health.

Mason and two additional researchers who spent their careers studying one or more of the B vitamins explain what we currently know about how the five of the most prominently researched B vitamins impact or improve cognitive as well as cardiovascular health.

Cognitive Health, B₁₂, and Folate

One of the most active areas for B vitamin research is cognitive health. By the age of 75-80, 40% of people have a diminished ability to absorb food-bound B₁₂, says Mason. This deficiency leads to a decline in nerve health, particularly in the spine and brain, which can contribute to the risk of developing dementia in older adults. 

For decades, clinicians and researchers thought measuring plasma B₁₂ was accurate enough to determine if supplementation was needed. However, Mason says, while many elderly people may have B₁₂ levels that are in the ‘low to normal’ range, they are simultaneously developing neurological deficits linked to vitamin B₁₂ deficiency. 

“The contribution of vitamin B₁₂ deficiency to cognitive decline and the vascular disease that results in many cases of dementia is under-diagnosed and under-reported,” says Irwin H. Rosenberg, Jean Mayer University Professor Emeritus at Tufts and former dean of the Friedman School of Nutrition Science and Policy who also taught pharmacology at the School of Medicine. 

“Age-related cognitive decline is not just Alzheimer’s,” says Rosenberg. “We’ve lumped together many kinds of brain dysfunction under one name. And in doing so, we’ve overlooked how critical blood vessels—and by extension, nutrition—are to preserving brain function.”

The pathology of Alzheimer’s disease described the abnormal buildup of two proteins in the brain—amyloid and tau—which clump together, forming plaques and tangles which are believed to disrupt brain cell function. 

Yet Rosenberg says cerebrovascular disease and small vessel disease, which in some cases are connected to B vitamin deficiency, is more prevalent with cognitive decline and dementia than the buildup of harmful proteins in the brain, which has been the focus of so much research and drug development to treat Alzheimer’s disease. Treating people with drugs meant to address the protein buildup will not work if the cause of dementia symptoms is a B₁₂ deficiency. 

Testing to identify whether cognitive decline and dementia symptoms may be caused by a B₁₂ deficiency is therefore imperative, he says. 

“B₁₂ tests measure all B₁₂ in your system, even though approximately 80% is inactive,” says Paul Jacques, senior scientist at the HNRCA and professor at the Friedman School of Nutrition Science and Policy. 

To pinpoint a B₁₂ deficiency requires two additional tests. One, called the MMA test, measures levels of methymalonic acid, an acid produced during certain aspects of metabolism requiring adequate B₁₂. “It can be elevated with even a mild B₁₂ deficiency, indicating a potential higher risk of dementia,” says Jacques. 

A second test measures levels of an amino acid, homocysteine, which is also a byproduct of metabolism requiring B₁₂. If only homocysteine levels are elevated, a folate deficiency may be the problem. If both MMA and homocysteine are high, a B₁₂ deficiency is the likely culprit.