Vitamin (fat-soluble)

• UK RNI None
• US RDA 80 mcg

Functions

• Production of four proteins involved in blood clotting
• Involved in bone calcification and mineralization

Good food sources

• Alfalfa
• Broccoli
• Brussels sprouts
• Cabbage and other leafy green vegetables
• Cauliflower
• Green tea
• Liver
• Meats
• Soybean, rapeseed and olive oils
• Tomatoes
• Whole grains

Deficiency signs and symptoms

• Bleeding and haemorrhage
• Increased urinary calcium excretion
• Osteoporosis

Preventing deficiency

Vitamin K can be synthesized by Bacteroides bacteria in the small intestine so it is not essential to obtain all vitamin K from the diet unless these bacteria have been depleted by taking antibiotics. Bacterial synthesis alone is not sufficient to meet all the body's needs. Vitamin K produced by bacteria in the colon is not absorbed.

Since vitamin K is fat-soluble, the presence of chronic diarrhoea, or any defect in fat digestion and absorption, or a deficiency of fat or oil in the diet, could result in depletion of vitamin K levels. About 60-70 per cent of dietary vitamin K is excreted daily, so a daily intake of vitamin K-rich foods is advisable. The long-term use of aspirin-based medication increases vitamin K requirements.

Comments

The plant form of vitamin K is known as phylloquinone (sometimes known as vitamin K1). Intestinal bacteria synthesize a family of compounds with vitamin K activity known as menaquinones (vitamin K2). Liver stores of vitamin K are small, and mainly consist of menaquinones. Bone contains substantial concentrations of both phylloquinone and menaquinones.

Vitamin K is often given routinely to newborn, especially premature, babies to prevent haemorrhagic disease of the newborn. Newborn infants have a low vitamin K level due to the lack of gut bacteria in the first few days of life. Proteins found in bone tissue - known as osteocalcin, bone Gla protein and matrix Gla protein - depend on adequate vitamin K levels, which may explain why supplementation with this nutrient helps to reverse osteoporosis.

SUPPLEMENTATION

In research studies, Vitamin K supplements have been found to:

• Accelerate healing of bone fractures
• Increase bone formation in post-menopausal women with osteoporosis
• Reduce the amount of calcium excreted in urine

Preferred form and suggested intake

Vitamin K supplements are not normally recommended since for most purposes more than adequate amounts of the vitamin can be obtained from vegetables.