The results contradict National Institutes of Health (NIH) findings that B6 inadequacies are rare in the US. It is one of the largest epidemiological studies to evaluate B6 levels. The study identified four groups as being particularly deficient in the nutrient: women of reproductive age especially current and former users of oral contraceptives; male smokers; non-Hispanic African-American men; and over-65s. "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 two milligrams per day," said Martha Savaria Morris, PhD, an epidemiologist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts. Vitamin B6 has been linked to heart health and immune system function and is important for red blood cell performance. Deficiencies can cause anaemia. "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," the researchers wrote. The study, published in the May issue of the American Journal of Clinical Nutrition, analysed blood samples of a varied sample of 7822 men and women aged one year or older, some of whom were supplement users. The data was collected from the 2003-2004 National Health and Nutrition Examination Survey (NHANES) and looked for plasma pyridoxal 5'- phosphate (PLP) levels, which is a co-factor in many important bodily functions such as amino acid metabolism and some enzymatic reactions. For the purposes of the study, PLP levels of less than 20 nmol/L were deemed to be inadequate in both men and women. Eleven per cent of supplement users and nearly a quarter of non-users demonstrated plasma PLP blood levels of less than 20 nmol/L, with a higher incidence among the highlighted sub-groups. Women Contraceptive-using women of child-bearing age (ages 13 to 54), recorded significantly lower PLP levels. "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," said Morris. "Most importantly, the data suggest 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." Menstruating women also recorded lower PLP levels but the researchers would not be drawn on a direct link between contraceptive use and vitamin B6 deficiency. "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," they said. Further study Morris emphasised the study demonstrated association not causation and called for further research in the area. "We have identified populations with a high prevalence of apparently inadequate vitamin B status," Morris 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." PLP levels are commonly used to inform Recommended Dietary Allowances (RDAs) for vitamin B6. The RDAs for vitamin B6 in men and women who are not pregnant or lactating are 1.3mg per day for men and women ages 19-50; 1.7mg per day for men over 50 and 1.5mg for women over age 50. Source: American Journal of Clinical Nutrition Volume 87, pages 1446 -54. "Trends of Vitamin B6 Status in US Population Sample" Authors: Morris MS, Picciano, MF, Jacques PF, Selhub, J.