What is vitamin K (phylloquinone)?

Discovered in 1929, vitamin K is the collective name for a group of three different compounds, the most common being vitamin K1 or phylloquinone. There's also K2 or menaquinone as well as K3 or menadione. Vitamin K is a fat soluble vitamin so some fats or oils are needed in the diet so it can be taken up into the body from the digestive tract.

What does vitamin K do in the body?

Vitamin K is used to make proteins that help our blood clot which is why it's so important for healthy blood and normal clotting. For this very reason, it's given to babies just after they're born (read more below).

Anyone who takes medication to keep the blood thin e.g. Warfarin and Heparin, will generally be told to keep their vitamin K intake at a steady level each day, neither too much nor too little. Greatly varying intakes of vitamin K - such as two large salads one day and no vegetables at all the next - can stop these medication from working properly.

Vitamin K helps protect your bones from fracture and also slows postmenopausal bone loss. In addition, it helps prevent calcification of your arteries.

How much do I need?

Women need 60 micrograms (mcg) while men need 70 micrograms (mcg) of the vitamin each day.

Adequate Intakes for vitamin K per day are:

     (From NHMRC Australia 2006):

• 2.0 mcg for babies (0 to 6 months)
• 2.5 mcg for babies (7 to 12 months)
• 25 mcg for toddlers (1 to 3 years)
• 35 mcg for schoolchildren (4 to 8 years)
• 45 mcg for schoolchildren (9 to 13 years)
• 55 mcg for teenager (14 to 18 years)
• 60 mcg for women
• 70 mcg for men
• 60 mcg for pregnant women
• 60 mcg for breastfeeding women.

mcg means micrograms

Safe upper limit for vitamin K

Safe even at quite high intakes

Best food sources of vitamin K

Vitamin K is found in a wide variety of foods but particularly excellent sources are green vegetables, many types of lettuce, berries and dried herbs. Good sources include meat, milk and grains. Cooking doesn't affect it but freezing may destroy some. Here's a list:

• Green vegetables (spinach, silverbeet, Swiss chard, Asian greens e.g. bok choy, asparagus, green beans)
• Kale, cabbage, broccoli, cauliflower - fresh, cooked and frozen
• Dark-green salad leaves (watercress, rocket or arugula, dark lettuces, radicchio, mustard greens, beet greens)
• Dried herbs e.g. thyme, sage, coriander, basil, marjoram, mixed Italian herbs
• Fresh green herbs (basil, parsley, chives, rosemary etc.)
• Liver
• Eggs
• Cheese
• Wholemeal flour
• Wholemeal and grainy breads
• Sea vegetables e.g. kelp

Vitamin K is made by the bacteria that live normally in our digestive tract. Newborn babies don't have bacteria established in their systems so they receive an injection of vitamin K immediately after birth to prevent bleeding.

Easy ways to get your recommended day's intake of 60 mcg

Vitamin K for newborn babies

In 2010, the NH&MRC confirmed its recommendation that all newborn babies receive an injection of vitamin K soon after birth. Babies do not get enough vitamin K from their mothers during pregnancy. Without vitamin K, they are at risk of getting a rare blood disorder called Vitamin K Deficiency Bleeding or VKDB. You can read the full report from the NHMRC website.

Vitamin K has been given to newborns for the past 20 years and seems to have caused no problems. The easiest and most reliable way to give babies vitamin K is by injection (1 mg or 0.1 mL of Konakion) at birth. This gives protection for a few months. By the age of six months, babies have built up their own supply.

Vitamin K can also be given by mouth. Several oral doses are needed to give enough protection, because vitamin K is not absorbed as well and the effect does not last as long.

What are deficiency symptoms for vitamin K?

Anyone deficient in vitamin K is likely to have symptoms related to difficulty in clotting or bleeding. These symptoms include heavy menstrual bleeding, bleeding gums, bleeding within the digestive tract, nose bleeds, prolonged clotting times, haemorrhage and anaemia.

A second set of vitamin K deficiency-related signs involves bone problems which can include loss of bone (osteopenia), loss of bone density (osteoporosis) and fractures.