Nearly two-fifths of the U.S.
population may be flirting with marginal vitamin B12
statusthat is, if a careful look at nearly 3,000 men and women in the
ongoing Framingham (Massachusetts) Offspring Study is any indication.
Researchers found that 39 percent of the volunteers have plasma B12
levels in the "low normal" rangebelow 258 picomoles per liter
While this is well above the currently accepted deficiency level of 148 pmol/L,
some people exhibit neurological symptoms at the upper level of the deficiency
range, explains study leader Katherine L. Tucker. She is a nutritional
epidemiologist at the Jean Mayer USDA Human Nutrition Research Center on Aging
at Tufts University in Boston.
"I think there's a lot of undetected vitamin B12 deficiency out
there," says Tucker.
She noted that nearly 9 percent of the study population fell below the current
deficiency level. And more than 16 percent fell below 185 pmol/L. "Many
people may be deficient at this level," she says. "There is some
question as to what the clinical cutoff for deficiency should be."
Deficiency can cause a type of anemia marked by fewer but larger red blood
cells. It can also cause walking and balance disturbances, a loss of vibration
sensation, confusion, and, in advanced cases, dementia. The body requires
B12 to make the protective coating surrounding the nerves. So
inadequate B12 can expose nerves to damage.
Tucker and colleagues wanted to get a sense of B12 levels spanning
the adult population because most previous studies have focused on the elderly.
That age group was thought to be at higher risk for deficiency. The researchers
also expected to find some connection between dietary intake and plasma levels,
even though other studies found no association.
Some of the results were surprising. The youngest groupthe 26 to 49 year
oldshad about the same B12 status as the oldest group65
and up. "We thought that low concentrations of B12 would
increase with age," says Tucker. "But we saw a high prevalence of low
B12 even among the youngest group."
The good news is that for many people, eating more fortified cereals and dairy
products can improve B12 status almost as much as taking supplements
containing the vitamin. Supplement use dropped the percentage of volunteers in
the danger zone (plasma B12 below 185 pmol/L) from 20 percent to 8.
Eating fortified cereals five or more times a week or being among the highest
third for dairy intake reduced, by nearly half, the percentage of volunteers in
that zonefrom 23 and 24 percent, respectively, to 12 and 13 percent.
The researchers found no association between plasma B12 and meat,
poultry, and fish intake, even though these foods supply the bulk of
B12 in the diet. "It's not because people aren't eating enough
meat," Tucker says. "The vitamin isn't getting absorbed."
The vitamin is tightly bound to proteins in meat and dairy products and
requires high acidity to cut it loose. As we age, we lose the acid-secreting
cells in the stomach. But what causes poor absorption in younger adults? Tucker
speculates that the high use of antacids may contribute. But why absorption
from dairy products appears to be better than from meats is a question that
needs more research.
Fortified cereals are a different story. She says the vitamin is sprayed on
during processing and is "more like what we get in
McBride, Agricultural Research Service Information Staff.
This research is part of Human Nutrition, an ARS National Program (#107)
described on the World Wide Web at