Why are people buying Vitamin K supplements?
There's been a wave of supplements launched containing Vitamin K, particularly K2. Why do people take them?
Not everybody will have heard of Vitamin K2.
But more and more of us are consuming it in supplements, according to market research firm Mintel.
It says new food, drink, vitamin and supplement product launches containing Vitamin K2 have gone up 183% globally between 2008 and 2012.
The better known form of Vitamin K, Vitamin K1, posted a healthy, but slower growth - 96% - over the same reviewed period.
The number of products containing Vitamin K1 still far outstrips those containing Vitamin K2. All types of Vitamin K were in 1% of all food, drink, vitamins and supplement launches last year, according to Mintel.
But what is Vitamin K, what's the difference between K1 and K2, and why are people taking Vitamin K supplements?
The NHS says Vitamin K has several important functions, for example blood clotting, which helps wounds heal properly. Babies are born with lower levels of Vitamin K, and for this reason the NHS offers an injection of it soon after birth to prevent internal bleeding problems.
There is also increasing evidence fat-soluble Vitamin K is needed to help build strong bones.
Adults need approximately 0.001mg a day of Vitamin K for each kilogram of their body weight, according to the NHS.
It says people should be able to get all they need by eating a varied and balanced diet, with any not needed immediately stored in the liver for future use.
It cites green leafy vegetables such as broccoli and spinach, vegetable oils and cereals as good sources of Vitamin K. Small amounts can also be found in meat such as chicken and dairy foods.
The NHS also advises that taking too many Vitamin K supplements might be harmful.
Those taking anticoagulants should also take heed of the experience of an Ayrshire man with a mechanical heart, who was hospitalised after his eating too many Brussels sprouts - which contain lots of Vitamin K - counteracted their effect.
So why are Vitamin K, and particularly Vitamin K2, supplements on the rise?
Laura Jones, a global food science analyst at Mintel, says recent research has revealed Vitamin K2 has much broader health benefits than previously thought, and is increasingly being seen as a bone health ingredient.
"Vitamin K1 has a relatively short half-life and is rapidly cleared from the blood and is cleared by the liver within eight hours. In comparison vitamin K2 has a longer half-life of up to 72 hours, meaning it remains biologically active in the body for longer.
"Vitamin K2 is also absorbed better by the body, and is linked to cardiovascular health. It directs calcium to the bones, and prevents it from being deposited where it shouldn't be, for example arteries and organs, where it can cause harm," she says.
The health claims for Vitamin K have had support from the European Food Safety Authority in recent years, with the body stating that "Vitamin K contributes to maintenance of normal bone," and "Vitamin K contributes to normal blood coagulation".
The ageing population - especially in major markets like Europe, Japan, China and the US - is also having an impact on supplement sales, with an increase in osteoporosis resulting in more interest in bone health.
The number of new products with bone health claims having grown 44% since 2009, according to Mintel.
And while calcium and Vitamin D continue to be the most common vitamins in food and supplements making a bone health claim, Jones thinks that as consumers' awareness of Vitamin K2 increases, so will its prevalence.
But not everyone is convinced.
Dr Sarah Jarvis, a general practitioner and regular guest on the BBC's The One Show, says there is no evidence to suggest that people aren't getting enough Vitamin K.
"I can see no reason why normal healthy people would need a Vitamin K supplement or any supplement - with the exception perhaps of Vitamin D - it's far better to have a balanced healthy diet," she says.
She thinks supplements send the wrong message.
"My feeling from young people that come into my clinic is that they think they can have a rubbish diet and take multi-vitamins to make up for it, which they can't.
"And if older people are worried about their bones, it's more important they look at calcium and Vitamin D. Vitamin K is connected with clotting - too much can have a negative impact if, for instance, you're taking medicine like warfarin," she says.