Vitamin K in the diet of the Irish population (1-90 years)

Abstract

Vitamin K is required to maintain normal blood coagulation and may also function in other areas including bone health and the inhibition of vascular calcification. The aim of this thesis was to estimate the intake, adequacy and dietary sources of vitamin K1 and vitamin K2 in the Irish population (1-90y) and to examine any changes in vitamin K1 or vitamin K2 intakes and sources in school-aged children (5-12y) between 2003-04 and 2017-18. This research was based on data from five nationally representative dietary surveys carried out by the Irish Universities Nutrition Alliance (www.iuna.net). These surveys included the National Children’s Food Survey (NCFS) (5-12y) (2003-04), the National Teens’ Food Survey (13-17y) (2005-06), the National Adult Nutrition Survey (18-90y) (2008-10), the National Pre-school Nutrition Survey (1-4y) (2010-11) and the NCFS II (5-12y) (2017-18). For each survey, dietary data were collected (at brand level) using weighed/semi-weighed food diaries. Each food, beverage and dietary supplement recorded was assigned a unique food code according to its food descriptor and nutritional profile. Using these food codes, the Irish Food Composition Database (IFCD) (2012) was updated to include food composition data for vitamin K1 and vitamin K2 (menaquinone-4 (MK-4) and menaquinones-5-10 (MK-5-10)). Vitamin K1 is typically found in green vegetables and certain plant oils. MK-4 is formed in mammals from the tissue specific conversion from vitamin K1 or from menadione (a synthetic form of vitamin K added to animal feed). The longer chained menaquinones, MK-5-10, are synthesized by bacteria capable of food fermentation and are found in fermented foods and foods of animal origin. As there are no analytical data available for vitamin K content of foods in Ireland, composition data for vitamin K1, MK-4 and MK-5-10 were assigned to each food code using published analytical values from the UK Composition of Foods Integrated Dataset, the United States Department of Agriculture National Nutrient Database or published papers, recipe calculation based on individual ingredients, and from nutritional information on product labels. In addition, foods that were either not fermented or of animal origin were assigned a composition value of 0µg for each menaquinone group. For a small number of food codes, vitamin K1 values were assigned based on the fat content of a similar product.. Overall, foods highest in vitamin K1 were herbs and ‘vegetable & vegetable dishes’. Foods highest in MK-4 and MK-5-10 were ‘meat & meat products’, ‘eggs & egg dishes’ and ‘cheese’. The distribution of vitamin K1 and vitamin K2 (MK-4 and MK-5-10) intakes in the Irish population were carried out using SPSS© for Windows™ Version 22.0. The mean intakes of vitamin K1 were above the European Food Safety Authority Adequate Intake (AI) of 1µg/kg/d (required to maintain normal blood coagulation) for children aged 1-12y. However, vitamin K1 intakes were below the same AI for teenagers aged 13-17y. ‘Vegetable & vegetable dishes’ (primarily green vegetables) was the key source of vitamin K1 for both children and teenagers. Mean intakes of MK-4 and MK-5-10 ranged from 8-13µg/d and 32-45µg/d in the Irish population aged 1-90y, respectively. The key dietary sources of MK-4 and MK-5-10 were ‘meat & meat products’, ‘milks’ and ‘cheese’. There was no difference in the intake and dietary sources of vitamin K1 or vitamin K2 in Irish children (5-12y) between 2003-04 and 2017-18. The data presented in this study will add to the small pool of data available on vitamin K intakes and sources in nationally representative samples of population groups. The Irish food composition database for vitamin K will support future researchers in the assessment of vitamin K intakes at individual or population level.