Interdependence of serum concentrations of vitamin K1, vitamin E,
lipids, apolipoprotein A1, and apolipoprotein B: importance in assessing
vitamin status
Vitamin E (α-tocopherol) and vitamin K1 (phylloquinone) are fat-soluble vitamins and are important nutrients in health and disease. In this study serum concentrations of vitamin E and vitamin K1, lipids and apolipoproteins A1 and B were measured in neonates, normal and hyperlipidaemic
individuals in an attempt to establish their interrelationships. A high
degree of correlation was observed between the concentrations of the
vitamins and those of lipids and apolipoproteins (r ranged from 0.42 to 0.92; p<0.001). Stepwise linear regression methods determined that serum concentrations of both vitamin E and vitamin K1 could best be predicted by using equations excluding lipids but containing only apolipoprotein A1 and B concentrations. Correlation coefficients between predicted and measured values were 0.89 for serum vitamin E, and 0.83 for serum vitamin K1 concentrations. To test the validity of the derived formulae, measured and estimated vitamin K1
and vitamin E concentrations in serum were determined in another group
of neonates, normal adults and hypercholesterolemic adults and the
comparisons were shown to be very good. These results indicate that the
serum levels of both vitamins depend critically on the concentration of
the lipoprotein carriers, apolipoproteins A1 and B. Hence, in order to identify variations in serum vitamin K1
and vitamin E concentrations, which are independent of variations in
carrier concentration, it will be necessary to express these serum
vitamins as ratios of vitamins to apolipoprotein A1 and B carriers.
Introduction
The fat-soluble vitamins K1
and E do not have specific physiological carriers in plasma. They are
transported by the plasma lipoproteins and are present in all
lipoprotein fractions, namely, chylomicrons, very-low-density
lipoproteins (VLDLs), low-density lipoproteins (LDLs) and high-density
lipoproteins (HDLs) [1], [2], [3]. There are strong similarities and
links between the metabolism of LDL and that of vitamin E. Vitamin E is
secreted from the liver in VLDL and is delivered to cells chiefly via
the high affinity receptor for LDL [4]. As for LDL, cells may also take
up the vitamin via a route, which is independent of the LDL receptor
[4], [5]. Serum concentrations of vitamin E are dependent on plasma
lipid concentrations [6]. For example in a hyperlipidaemic state the
absolute value of serum vitamin E concentration may be normal and the
subject still found to be vitamin E nutritionally deficient [7] Thus,
the use of a relative measure of plasma vitamin E (ratio of tocopherol
to total lipids or to cholesterol) has become essential in evaluating
vitamin E nutritional status in individuals or in populations [6], [8],
[9], [10].
The relation between vitamin K1
and serum lipids is less clear. Sadowski et al. assessed the vitamin K
nutritional status of individuals in different age groups [11]. The
authors noted that they obtained different results when they used a
ratio of vitamin to lipid rather than absolute concentrations of serum
vitamin as the index of nutritional adequacy [11]. Further studies in
neonates found that a series of very low absolute concentrations of
vitamin K1 in serum did not reflect the vitamin K status
[12]; serum lipid values were however not considered. Thus, despite the
limited evidence, it seemed probable that the interpretation of serum
vitamin K1 levels might require similar qualifications to those applying to vitamin E [10].
The present study has examined the interrelation between the concentration of serum vitamins K1 and E and some of their carrier lipoprotein components using vitamin E as a currently established marker.
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