In this brief technical article we examine the role of Vitamin K in health. We also look at the potential for supplementation and some of the research being conducted into this fascinating micronutrient.
The name and structure of vitamin K
Vitamin K was first identified by the Danish Chemist Henrik Dam. It eventually earned him the Nobel prize in 1943 for his discovery of its role as the K-oagulation factor in blood clotting.
Vitamin K is not a single chemical structure but actually refers to a group of fat-soluble vitamins. The two most common forms of vitamin K are K1 (phylloquinone) and K2 (menaquinone).
Vitamin K2 can be further subdivided into a family of closely related menaquinone molecules (MK’s). These differ in the length of their side-chain structure, the n representing the number of isoprenoid side chain residues.
Dietary sources
Plants are the principal dietary source of vitamin K accounting for around 90% of total vitamin K intakes. Rich sources include green leafy vegetables such as kale, broccoli and spinach.
K2 is found in animal based products (as MK-4) e.g. fatty meat and eggs and in fermented foods (as MK-7 to 9) e.g. cheese and Natto.
Natto, a fermented soy product commonly consumed in Asia, is the richest known dietary source of vitamin K2.
Vitamin K’s essential role in the body
K vitamins are critical co-factors for a variety of proteins in the body. These include those involved in blood clotting, calcium transport, insulin regulation, fat deposition, cell proliferation and DNA transcription.
Vitamin K as K1 is well known for its role in the blood-clotting cascade whilst K2 is best known for helping to regulate calcium transport and bone health. In the K2 form it can be stored in the body’s fatty tissues and the liver.
Vitamin K deficiency
Deficiencies of vitamin K are believed to be relatively rare given its abundance in green leafy vegetables although exclusively breast fed infants can be vulnerable.
Individuals relying on a Western diet may be receiving sub-optimal levels of K2. ThIs comes with the move away from dairy foods, lowered consumption of fatty and organ meats e.g. liver and the general lack of fermented foods.
The relatively poor inter-conversion between K1 and K2 can exacerbate a potential lack of vitamin K2. Small amounts of MK-4 can be formed via the metabolic conversion of K1 during its absorption in the intestinal mucosa and in other organs. However, this constitutes less than 20% of the body’s requirement for K2.
Gut bacteria in the large intestine also produce vitamin K2 although this routes contribution to the overall daily requirement has yet to be established.
Taking a food supplement
The US institute of Medicine has recommended a vitamin K intake range of 90-120 micrograms per day. The European Food Safety Authority (EFSA) has set an adult adequate intake (AI) level for K1 of 70 micrograms per day. Interestingly no intake level has been set specifically for K2. It has a different biological function to that of K1 and is the form most likely to be deficient.
Vitamin K appears to be very safe. The European Scientific Committee on Food (SCF) concluded that there was no appropriate evidence to determine a tolerable upper intake level.
Vitamin K can be purchased commercially as oil or in powdered form for use in supplements. K2 used in supplements is most commonly present in either the MK-4 or MK-7 isoform. MK-4 comes from synthetic manufacture while MK-7 is still commercially produced from Natto fermentation.
The dietary intake of vitamin K required for optimal function of all vitamin K-dependent proteins is not yet known. However, given the physiological importance of vitamin K supplements would appear to be of value.
Future interest in Vitamin K
There has been growing interest and research into the link between vitamin K status and the severity of certain COVID related symptoms.
Recent research published in the British Journal of Nutrition1, presents vitamin K metabolism as the potential missing link between lung damage and thromboembolism. These are two of the most serious outcomes observed in COVID-19 patients.
The researchers highlighted the need for further research to determine whether vitamin K supplementation has a place in treatment protocols, something that remains largely unexplored.
The role of vitamin K in Coronary heart disease (CHD) is another area where research to date has been sparse despite the known correlation.
A recent Norwegian community-based study population2, observed that intake of K2 was associated with lower risk of CHD. The researchers recommended a need for more studies on the noteworthy association between K2 and CHD.
These are just two examples amongst a plethora of exciting research which also includes the role of vitamin K in osteoporosis prevention as well as its link to life expectancy.
Such work continues to highlight the role of vitamin K in health and the valuable potential role of targeted nutritional prophylaxis.
References
1. Rob Jansen, Jona Walk, et al. Vitamin K metabolism as the potential missing link between lung damage and thromboembolism in Coronavirus disease 2019. British Journal of Nutrition (2021), 126, 191–198.
2. Haugsgjerd TR, Egeland GM, Nygård OK, et al. Association of dietary vitamin K and risk of coronary heart disease in middle-age adults: the Hordaland Health Study Cohort. BMJ Open 2020;10:e035953. doi:10.1136/ bmjopen-2019-035953.
https://bmjopen.bmj.com/content/bmjopen/10/5/e035953.full.pdf