Here’s our expert guide to getting your head around the vitamin, plus the top-selling vitamin K supplements from Boots.com
You might know the majority of your vitamin ABCs, but when it comes to vitamin K, you might not be as clued up – perfectly understandable as it does tend to get overlooked. But not anymore!
We ask the experts to give us the lowdown on everything vitamin K, from what it does and how much you need to the best food sources and how to decide if a vitamin K supplement is for you.
What is vitamin K and what does it do?
‘Vitamin K is a fat-soluble vitamin that plays an essential role in blood clotting and bone health1,’ explains Victoria-Jain Hamilton, registered nutritionist and founder of The Autoimmunity Nutritionist. ‘The body needs it to produce a protein called prothrombin, which is key for these2.'
What are the food sources of vitamin K?
There are three types of vitamin K: K1 (which we get through our diet), K2 (which is made by bacteria in our intestines) and K3 (a synthetic water-soluble type that’s used as a treatment for adults)3.
Vitamins K1 and K2 can be found in a range of dietary sources and are stored in your fat tissue and liver4. ‘You can find vitamin K1 in green vegetables, such as kale, spinach, broccoli, lettuce and swiss chard,’ says Azmina Govindji, dietitian and spokesperson for the British Dietetic Association. You can also find it in vegetable oils, such as soybean and canola oil5. Sources of vitamin K2 include fermented soybeans and eggs6.
Diet-derived vitamin K can also be found in cereal grains and small amounts can be found in meat and dairy products.
How much vitamin K do you need per day?
‘The UK acceptable intake is 1mcg per kg of your body weight,’ explains Azmina. ‘So, if you weigh 60kg, an acceptable daily amount would be 60mcg.
‘You should be able to get all the vitamin K you need if you eat a balanced range of foods that includes green, leafy vegetables.’
According to the NHS, any vitamin K your body does not need immediately is stored in the liver for future use, so you do not need to include it in your diet every day.
The good news is that it’s easy to obtain from any meal. ‘As it’s a fat-soluble vitamin, it’s more efficiently absorbed if you have it at the same time as a food that contains fat, so try adding an oil-based dressing to your green salad7,’ suggests Azmina.
Are vitamin K supplements necessary?
If you eat a healthy and balanced diet, you should be able to meet all your vitamin K requirements. An oral supplement may help support this, but there isn’t any evidence to show that it’s an essential.
But if you do choose to take one, it’s important to bear in mind that food supplements are intended to supplement the diet and should not be substituted for a varied diet or healthy lifestyle.
While taking 1mg or less of vitamin K daily is unlikely to be harmful, according to the NHS there’s not enough evidence to know what the effects might be of taking high doses daily.
Who should consider taking a vitamin K supplement?
It could be worth looking at a supplement if you’re on antibiotics. ‘As antibiotics can destroy vitamin-K-producing gut bacteria8, it might be worth supplementing with vitamin K to improve levels,’ suggests Victoria-Jain. So, if your course lasts for a few weeks or it causes you to have a poor appetite, it may be something to consider.
‘In addition, as vitamin K is fat soluble, cholesterol-lowering medication may interfere with vitamin K absorption, so people taking these medications have a higher risk of deficiency,’ says Victoria-Jain. There are those with malabsorption conditions that may also make them more prone to vitamin K deficiency. Speak to your GP or pop in store for a chat with your Boots Pharmacy team to talk through options best suited for your needs.
And if you are thinking of taking a vitamin K supplement, but are on blood-thinning medication, such as warfarin, see your doctor or pharmacist before taking, because of the impact vitamin K can have on blood coagulation/clotting.
What vitamin K supplements are there?
A diet-first approach is best when it comes to getting your recommended quota, particularly if you’re taking warfarin as you need to keep your intake of vitamin K-rich foods about the same each day. However, this doesn’t apply if you’re taking other anticoagulant medicines, such as apixaban or dabigatran, but you should check with your GP, anticoagulant clinic or pharmacist if you’re not sure.
If you do choose to support your levels with a dietary supplement, here are three of the top-selling vitamin K supplements at Boots.com to consider, though it’s also worth noting that vitamin K is rarely sold separately and is usually alongside other vitamins, as is the case here. Have a browse of the full range of vitamin K supplements to find more.
