Menaquinones, Bacteria, and the Food Supply: The Relevance of Dairy and Fermented Food Products to Vitamin K Requirements

Abstract

Vitamin K exists in the food supply as phylloquinone, a plant-based form and as menaquinones (MKs), a collection of isoprenologues mostly originating from bacterial synthesis. Although multiple bacterial species used as starter cultures for food fermentations synthesize MK, relatively little is known about the presence and distribution of MK in the food supply and the relative contribution of MK to total dietary vitamin K intake. Dairy products may be a predominant source of dietary MK in many regions of the world, and there is recent interest in enhancing the MK content of dairy products through identification and selection of MK-producing bacteria in dairy fermentations. This interest is increased by emerging evidence that current dietary recommendations based on the classic role of vitamin K as an enzyme cofactor for coagulation proteins may not be optimal for supporting vitamin K requirements in extrahepatic tissues and that MK may have unique bioactivity beyond that as an enzyme cofactor. Observational studies have reported favorable associations between MK intake and bone and cardiovascular health. Although randomized trials have provided some evidence to support the beneficial effects of MK on bone, the evidence to date is not definitive, and randomized trials have not yet examined MK intake in relation to cardiovascular outcomes. Food production practices provide a means to enhance dietary MK availability and intake. However, parallel research is needed to optimize these production practices, develop comprehensive food MK content databases, and test hypotheses of unique beneficial physiological roles of MK beyond that achieved by phylloquinone.

Coprophagy in nineteenth-century psychiatry

“…Clinicians dealing with this challenge may wish to consider the growing evidence of the importance microbial ecology in human mental and general health, particularly in relation to microbes that: (a) generate the neuroprotective short-chain fatty acids n-butyrate, acetate, and propionate as by-products of their own metabolism [62]; (b) synthesise Menaquinones (vitamin K2) which play an important role in bone remineralisation and calcium regulation – of particular relevance to osteopenia in the elderly [63]; (c) produce indoles such as indolamine-2,3-dioxygenase, which act as catalysing enzymes in tryptophan synthesis, with corresponding beneficial effects on the gut epithelium, but also on serotonin synthesis [64,65]. They might also wish to consider the bacterial species that have been found to upregulate neurotransmitters and neurotransmitter precursors, including GABA, Dopamine, 5HT, and acetylcholine – of particular relevance to mental illness and to neurodegenerative diseases such as Alzheimer’s and Parkinson’s [66].…”

Menaquinones, Bacteria, and Foods: Vitamin K2 in the Diet

“…The isoprenoid side chain is synthesized separately and is joined to the naphthoquinone ring to form demethylmenaquinone. Prenylation and methylation catalyzed by polyprenyltransferase (MenA) and methyltransferase (MenG) are the last steps of the synthesis of menaquinone [16,17]. An alternative pathway, called the futalosine pathway, was described in microorganisms that lack men genes.…”

“…Vitamin K2 is mostly synthesized by bacteria; therefore, the highest number of long-chain menaquinones is found in fermented dairy products, such as cheese and fermented vegetables, such as natto and sauerkraut [16]. One exception is MK-4, which is formed by a realkylation step from menadione present in animal feed or as a product of tissue-specific conversion directly from dietary phylloquinone [5].…”

New Perspectives for the Nutritional Value of Vitamin K in Human Health

“…Phylloquinone contains a phytyl side chain, which has only one unsaturated bond, and is found in plants and cyanobacteria [18,19]. Menaquinones are predominantly produced by bacteria and composed by a side chain with repeating isoprene residues, each containing an unsaturated bond [18][19][20]. In human diet their main sources are fermented foods represented by cheese and curd in Western diets, and the traditional Japanese food made from soybeans, natto.…”

“…In human diet their main sources are fermented foods represented by cheese and curd in Western diets, and the traditional Japanese food made from soybeans, natto. Depending on the number of prenyl repeats, menaquinones are subcategorized as MK-n, with n corresponding to the number of isoprenoid units, generally ranging from 4 to 13 [18][19][20]. MK-4 and MK-7 are commonly used as vitamin K2 supplements.…”