Taken by millions of Brits and Americans in the pursuit of achieving optimum health, vitamins and supplements are a multi-billion-pound industry.

However, experts warn taking certain combinations of them can be dangerous.

Potential harms of mixing popular vitamin pills range from deficiencies to even organ damage.

The riskiest pairing comes with taking red yeast rice extract and niacin — said to help lower cholesterol.

Todd Sontag, a family medicine specialist with Orlando Health Physician Associates in Florida warned that both products together could potentially cause liver damage.

What's more, Mr Sontag explained, the supposed benefits to heart health of taking the supplements is not rooted in good evidence.

'Doubling up doesn't increase the benefits and may be harmful to the liver,' he told wellness website The Healthy. 

This risk is heightened if other cholesterol-lowering substances, like statins, are added into the mix.

Cases where medics have found patients suffering serious liver injury from taking red yeast rice extract supplements have been documented previously. 

One common risk of taking different vitamins or supplements at the same time is that they counteract each other, which could leave you facing a potential vitamin or mineral deficiency.

Taking magnesium and calcium supplements at the same time is one example.  

For this reason, Dr Tod Cooperman, president of ConsumerLab, a New York-based company that tests health and nutrition products, recommends spacing out high-dose magnesium and calcium supplements by at least two hours, as they can otherwise compete for absorption.

Magnesium helps the body turn the food we eat into energy while calcium intake is crucial for bone health.

A similar interaction also occurs with potassium, a mineral key to good heart health, and calcium, as well as with zinc and copper.

The NHS warns that too much zinc can interfere with absorption of copper — a mineral we need for producing bloods cells and supporting bone health. 

If we don't get enough copper we can suffer anaemia and weakening of the bones, the health service warns. Again, experts advise spacing dosage of supplements by two hours to reduce this risk. 

A host of vitamins that are absorbed with fat during digestion, medically known as fat-soluble vitamins, should also not be taken together.

This includes vitamins A, D, E and K and if you need to take supplements of these ensure you space them out by a couple of hours during the day to maximise absorption.

Those who enjoy a brew might also want to avoid taking iron supplements at the same time, experts say.

Iron is crucial nutrient in making red blood cells which carry oxygen around the body.

However, if taken alongside a cup of black or green tea, iron supplements can bind to tannins, the plant compounds that are found in tea instead of being absorbed by the body.

This interaction only occurs if both tea and iron supplements are taken directly together.

It is also a good idea to be cautious about combining sleep boosting substances such as melatonin and herbal supplements like valerian, ashwagandha, kava, and St. John's Wort. 

While by themselves they should be harmless, a combination could lead to unexpected drowsiness that could prove dangerous. 

 Although not technically a supplement combination, experts are also keen to highlight the dangers of taking some health supplements with certain medications.

The most important of these is St. John's Wort and antidepressants. 

Both can boost levels of serotonin, a 'feel good' hormone, in the body to dangerous levels leading to a condition called serotonin syndrome.

This can trigger confusion, agitation, twitching, sweating, shivering and diarrhoea but in severe cases can lead to potentially dangerous seizures and an irregular heartbeat.

Lastly, iron supplements can interfere with some antibiotics, a class of drugs used to treat infections, stopping them from working.

Those prescribed these drugs should be cautious about taking them together, experts said. 

The NHS says most people should get all the nutrients they need by having a varied and balanced diet.