Nearly two-fifths of the U.S. population may be flirting with marginal vitamin B12 status if the population of Framingham, Mass., is any indication.
A careful look at 3,000 men and women in the ongoing Framingham Offspring Study found 39 percent with plasma B12 levels in the "low normal" range--below 258 picomoles per liter.
While this is well above the currently accepted deficiency level of 148 pmol/L, some people exhibit neurological symptoms in the higher range, said study leader Katherine Tucker. She is a nutritional epidemiologist at the Jean Mayer U.S.D.A. Human Nutrition Research Center on Aging at Tufts University in Boston.
Nearly nine percent of the study population fell below the current deficiency level. And in excess of 16 percent fell below 185 pmol/L. "Many people may be deficient at this level," said Tucker. "There is a question as to what the clinical cutoff for deficiency should be.
"I think there is a lot of undetected vitamin B12 deficiency out there," she said, noting that the study covered people from 26 to 83 years old. The research was funded by the Agricultural Research Service (ARS), U.S.D.A.'s chief scientific agency.
B12 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.
"The good news," said ARS administrator Floyd Horn, "is that most people can enhance their B12 status by eating more fortified cereals and dairy products. Dr. Tucker's findings show that these foods were nearly as effective as supplements containing B12 for getting people's blood levels above the danger zone."
Tucker and colleagues looked at B12 levels spanning the adult population because most previous studies have focused on the elderly, who were thought to be at higher risk for deficiency. The results were surprising. The youngest group--the 26- to 49-year-olds--had about the same B12 status as the oldest group--65 and up. "We saw a high prevalence of low B12 even among the youngest group," Tucker said.
The researchers also expected to find some connection between dietary intake and plasma levels, even though other studies found no association. And they did find a connection. 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 5 or more times a week or being among the highest 3rd for dairy intake reduced, by nearly half, the percentage of volunteers in that zone--from 23 and 24 percent, respectively, to twelve and 13 percent.
Oddly, the researchers found no association between plasma B12 levels 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 said. "The vitamin isn't getting absorbed."
In the elderly, it's probably because they don't secrete enough stomach acid to separate the vitamin from the meat proteins that tightly bind it. But Tucker can only speculate about the reasons for poor absorption of the vitamin from meat among younger adults or why B12 appears to be better absorbed from dairy products than from meats.
Fortified cereals are a different story. Tucker said the vitamin is sprayed on during processing and is "more like what we get in supplements."
