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Bioavailability of vitamin K1 in the UK diet and the relationship of intake to status
Project Code: N05050
Using data from 7 day weighed dietary records, dietary intake and sources of phylloquinone (vitamin K1) were examined in 1916 participants aged 16–64 years from the 1986/7 Dietary and Nutritional Survey of UK Adults, and 1423 participants aged 19–64 years from the 2000/1 National Diet and Nutrition Survey.
Vitamin K1 plasma status was measured using high performance liquid chromatography in 1154 plasma samples collected as part of the 2000/1 National Diet and Nutrition Survey.
Vitamin K1 enriched with stable isotopes of carbon and hydrogen was used to measure the metabolism and bioavailability of absorption. The in vivo fate of the labelled compounds was measured by mass spectrometry. As Vitamin K1 is found at very low concentrations in plasma and it was necessary to purify vitamin K1 from other compounds. New extraction, derivatisation and gas chromatography/mass spectrometry procedures were developed to allow the accurate measurement of labelled vitamin K1 in plasma.
Using these methods, two human volunteer studies were performed. The first study measured the kinetics of vitamin K1 in body pools, after an intravenous injection, in 10 volunteers. At the same time, the volunteers also consumed a capsule form of vitamin K1 labelled with a stable isotope and absolute values for vitamin K1 absorption were calculated by combination of the data from the injected and oral doses. The second volunteer study used data from the assessment of dietary intake of vitamin K1 in the Dietary and Nutritional Survey of British Adults to design meals typical of those consumed in the UK, from which to measure vitamin K1 absorption.
Analysis of dietary intake data showed that around 60 % of vitamin K1 comes from vegetables. Intakes in the UK have decreased between 1986/7 and 2000/1 mainly due to a decrease in green leafy vegetable consumption.
Mean vitamin K1 plasma concentration in the 2000/1 National Diet and Nutrition Survey was 0.94 nmol/L, but men (1.13 nmol/L) were found to have significantly higher plasma vitamin K1 than women (0.81 nmol/L).
From the stable-isotope volunteer experiments, vitamin K1 turnover was measured as 0.34 µg / kg per day and absorption of vitamin K1 from the capsule was only 13 %,which was lower than previous estimates. Results from the meal studies demonstrated a useful approach for the measurement of vitamin K1 absorption and showed that vitamin K1 absorption was poorer for the cosmopolitan and animal-orientated diets, compared to a convenience diet.
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