Objective: To examine the relationship between dietary phylloquinone intake and vitamin K status of postmenopausal Caucasian women.
Design: Cross-sectional study, in which dietary intake was estimated using weighed record techniques and vitamin K status was measured by a single plasma phylloquinone concentration and 24-h urinary gamma-carboxyglutamic acid (Gla) excretion.
Setting: The metabolic research unit at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University, Boston, MA.
Subjects: 402 healthy postmenopausal Caucasian women who were participating in a randomized trial to determine the effect of calcium supplementation on bone loss. Of the original group, 362 had complete weighed diet records, 358 had corresponding plasma phylloquinone concentrations, and 346 had corresponding urinary Gla measurements.
Results: There was a significant correlation (r = 0.13, P = 0.01) between total dietary intake of phylloquinone (geometric mean = 89 micrograms/day) and plasma phylloquinone levels (mean = 1.12 nmol/l). Dietary intake was neither correlated with urinary Gla excretion (mean = 4.0 mumol/mmol creatinine) nor did it vary by season. The ratio of intra- to interindividual variance in phylloquinone intake was 2.6, from which it was estimated that 5 days of independent recording is necessary to estimate true usual dietary intake, assuming a correlation of 0.8.
Conclusions: A weighed record has the potential to be a reliable method for estimating dietary intakes of vitamin K which relate to plasma phylloquinone levels used as an indicator of vitamin K status in postmenopausal Caucasian women.