Relationships between dietary intakes and fasting plasma concentrations of fat-soluble vitamins in humans.

Dietary intakes of retinol equivalents, alpha-tocopherol equivalents, vitamin D and phylloquinone were estimated from three sets of 4-d weighed diet records and compared to three corresponding fasting plasma concentrations of retinol, 25-hydroxyvitamin D, alpha-tocopherol, and phylloquinone measured in 34 healthy adults over 20 wk. The magnitude of the correlation between dietary vitamin intake and its corresponding biochemical measure is in part determined by the reproducibility of each of the measures, so within-to-between subject variance ratios were calculated for both dietary intakes and plasma concentrations. Phylloquinone was the only fat-soluble vitamin with a significant correlation between dietary intake and fasting plasma concentration (r = 0.51, P = 0.004). This correlation improved with an increase in both the number of independent diet records and independent plasma measures. Of the dietary intake measures, all the fat-soluble vitamins had greater within than between subject variance, with the highest measured for phylloquinone (6.86:1). Of the plasma measures, only phylloquinone had a within-to-between subject variance ratio greater than one (5.36:1). Comparisons across age and sex for dietary intake and plasma concentrations differed in pattern among the fat-soluble vitamins.