Almost one million Brits have been issued a caution regarding certain supplements, as they could react badly to a medication they are on. According to an expert, combining these pills could be “harmful”.

A dietitian identified three commonly used supplements which could be hazardous if taken alongside warfarin, a medication frequently prescribed to thin the blood.

It’s believed that approximately 1.5 per cent of the UK population, equating to around 700,000 individuals, are on warfarin.

Victoria Taylor, dietitian for the British Heart Foundation (BHF), explained more in an article for the charity’s Heart Matters magazine. Firstly, Victoria warned that it is always best to eat a healthy, balanced diet without the need to rely on supplements.

She said: “Many different supplements are available in the shops and on the internet, some of which make claims about improving general health and specific conditions like heart disease. But these claims are not always true.”

Furthermore, she warned: “Taking a supplement cannot undo the negative effects of an unhealthy diet. Research also shows that supplements do not help to stop or improve heart and circulatory diseases. In some cases, supplements can even be harmful.”

She also dispelled the common notion that supplements are healthier due to their higher concentrations of vitamins and minerals. She clarified: “You may think supplements are healthier than food because they contain high levels of vitamins and minerals. But more is not always better. Having too much of some vitamins and minerals can be bad for your health.”

Mixing supplements with warfarin

Victoria highlighted the potential risks associated with mixing certain supplements with medicine, particularly calling out vitamin K, omega-3, and St John’s wort. She drew attention to their negative interactions with the blood thinner warfarin, which could lead to detrimental side effects.

“Some supplements can also affect the medicines you are taking, causing side effects,” she warned. “For example, vitamin K, omega-3 and St John’s wort all interact with the blood-thinning drug warfarin.”

The NHS has also advised caution when combining some herbal remedies with warfarin. Its official guidance cautions: “Do not take St John’s wort, the herbal remedy for depression, while you’re taking warfarin. It can increase your risk of side effects.”

Moreover, the health service recommends a consultation with a GP prior to taking vitamin K if already on warfarin. The NHS instructed: “Tell your doctor if you’re taking vitamin K supplements before you start taking warfarin. Do not start taking vitamin K supplements while you are taking warfarin without checking with your doctor first.”

NICE has highlighted specific worries regarding the increased bleeding risk when warfarin is used alongside omega-3-acid ethyl esters. It said: “Warfarin causes bleeding, as can omega-3-acid ethyl esters; concurrent use might increase the risk of developing this effect.” The manufacturer’s instructions also advise caution or avoidance of such combinations.

For individuals considering adding supplements to their health routine, Victoria recommends consulting a GP before taking any action, underlining the necessity of expert advice. She advised: “Talk to your doctor before spending money on supplements. If you need them they will prescribe or recommend them.”

She points out that the only routine vitamin supplement universally suggested is vitamin D. Victoria further explained: “The exception to this is that it is recommended we all take 10 micrograms a day of vitamin D supplement in the autumn and winter, because vitamin D is mainly made in our bodies with the help of sunlight.

“Just a little comes from food. Apart from this, a healthy, varied, balanced diet provides all the energy, vitamins and minerals you need.”