Tufts: Study identifies trends of vitamin B6 status in US population sample

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Public release date: 20-May-2008

http://www.eurekalert.org/pub_releases/2008-05/tuhs-sit052008.php

Contact: Grossman

Tufts University, Health Sciences

Study identifies trends of vitamin B6 status in US population sample

BOSTON- (May 20, 2008) In an epidemiological study, Tufts University

researchers identified trends of vitamin B6 status in a sample of the

United States population based on measures of plasma pyridoxal 5'-

phosphate (PLP) levels in the bloodstream. Plasma PLP is the indicator

used by the federal government to set the current Recommended Dietary

Allowance (RDA) of vitamin B6, a nutrient essential for red blood cell

function and important for maintaining a healthy immune system and blood

glucose levels.

" Across the study population, we noticed participants with inadequate

vitamin B6 status even though they reported consuming more than the

Recommended Daily Allowance of vitamin B6, which is less than 2

milligrams per day, " says Martha Savaria , PhD, an epidemiologist

at the Mayer USDA Human Nutrition Research Center on Aging at Tufts

University. " We also identified four subgroups where this trend seemed

most prominent: women of reproductive age, especially current and former

users of oral contraceptives, male smokers, non-Hispanic

African-American men, and men and women over age 65. " Someone with

inadequate vitamin B6 status is at risk of becoming Vitamin B6 deficient

should their vitamin B6 levels drop too low.

Corresponding author and colleagues studied 7,822 blood samples

of men and women ages one-year and older collected from the 2003-2004

National Health and Nutrition Examination Survey (NHANES). Vitamin B6

inadequacy was defined as a plasma PLP concentration less than 20

nmol/L. To the authors' knowledge, the current study is the first large

scale study to use plasma PLP concentrations to evaluate vitamin B6

status in free-living people of all ages. The investigators were also

able to consider whether the current RDA guaranteed adequate vitamin B6

status because study participants were questioned about supplement use

and two days' worth of food intake.

Eleven percent of supplement users and nearly a quarter of non-users

demonstrated plasma PLP blood levels of less than 20 nmol/L. Within the

four sub-groups where vitamin B6 inadequacy was most prominent, the

prevalence of low plasma PLP levels significantly exceeded 10

percent©¤even among those who consumed 2 to 2.9 milligrams per day of

vitamin B6. The RDAs for vitamin B6 in men and women who are not

pregnant or lactating are as follows: 1.3 mg per day for men and women

ages 19-50, 1.7 mg per day for men over age 50 and 1.5 mg for women over

age 50.

Writing in the May 2008 issue of the American Journal of Clinical

Nutrition, and colleagues noted a stark contrast in plasma PLP

levels between women of childbearing age (ages 13 to 54) and their male

peers. " When we looked specifically at the plasma PLP levels in women of

childbearing age, we noticed they were significantly lower than in males

in approximately the same age group. " continues, " Most

importantly, the data suggest that oral contraceptive users have

extremely low plasma PLP levels. Three quarters of the women who

reported using oral contraceptives, but not vitamin B6 supplements, were

vitamin B6 deficient. "

A pattern of low vitamin B6 status also surfaced in menstruating women

who reported using oral contraceptives but who were no longer using them

at the time of the NHANES survey. Among women in this sub-group who were

not taking vitamin B6 supplements, 40 percent demonstrated plasma PLP

blood levels below the cut-off for vitamin B6 inadequacy. says,

that although these results are somewhat surprising, the link between

oral contraceptive use and vitamin B6 deficiency remains unclear. " The

vitamin could be stored elsewhere in the bodies of the oral

contraceptive users, or in a different form, since our study only

examined plasma PLP. "

To further support their findings, and colleagues measured

homocysteine levels in the blood and compared them against the plasma

PLP measures. Homocysteine is an amino acid that can accumulate in the

blood if vitamin B6 levels are too low. Though study participants using

oral contraceptives at the time of the survey did not demonstrate

elevated homocysteine levels, the homocysteine concentrations of former

users were significantly higher than those of women who had never used

oral contraceptives. says this could mean that oral contraceptive

use has an effect on vitamin B6 status that is masked during use by

acute effects of the exposure.

Because the study shows association and not causation, stresses

that further research is necessary to determine whether the RDA for

vitamin B6 is high enough. " We have identified populations with a high

prevalence of apparently inadequate vitamin B status, " says.

" However, it is important to recognize that signs of deficiency are not

seen at plasma PLP concentrations of 20 nmol/L and that dietary

assessment is imperfect. "

According to the National Institutes of Health (NIH), vitamin B6

deficiency is rare in the United States, but it can cause a form of

anemia similar to iron deficiency anemia. Vitamin B6 is widely

distributed in the American diet, and baked potatoes, bananas, 100

percent fortified cereals and chicken are particularly good sources.

says, " The question our study raises is whether, due to aging,

genetics, or exposures, some population subgroups need supplements to

achieve the current biochemical definition of adequate status. "

###

This study was supported by the National Institutes of Health and by the

U.S. Department of Agriculture.

MS, Picciano, MF, Jacques PF, Selhub, J. American Journal of

Clinical Nutrition. 2008 (May); 87: 1446-54.

--

ne Holden, MS, RD

" Ask the Parkinson Dietitian " http://www.parkinson.org/

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