Lots of people take vitamins, minerals and other remedies they buy from health shops – so called ‘over the counter’. It is a massive industry – estimated to be worth £1.86b in the UK alone. Is this just clever marketing?

The fact remains that a normal varied diet in the UK will provide all the nutrients you need. Even vegetarians do not normally need to take supplements. One of the commonest supplements is vitamin C but I have never seen a case of scurvy – vitamin C deficiency – in my lifetime. Vitamin C does not prevent colds or infections; this has been researched for over 20 years and shown not to work. Vitamin C is water soluble and so most of it is simply eliminated in the urine, but high doses can produce excess acid in the blood causing heart and kidney problems. This can be an issue with an operation so I ask patients to stop a t least a week before.

A concern for doctors is that we never actually know what the patient is taking. If you are prescribed a drug it will have gone through years of rigorous testing and the actual contents will have to be published, but supplements are not regulated in the same way and the ingredients, if listed at all, are often in the form of plants and vegetables as opposed to chemical composition. The risk of an interaction with anaesthetics or other drugs is always in the back of my mind.

If a doctor has told you to take a supplement then please do so, but always remember to bring the supplement in its original container to hospital for me to see.

So are there any other exceptions? Well, patients who are anaemic may be given iron supplements. That is fine, but I normally stop them for five days before an operation and for a couple of weeks after to avoid unpleasant constipation. A moderately low blood count is actually quite good for anaesthesia.

Recent research suggests that both men and women lack vitamin D in the winter in the UK due to a lack of sunlight, so a single vitamin D3 tablet each day is a good idea. The recommended dose is 1000 international units – much higher does can be bought over the counter but these are for short term use only.

There is some evidence folic acid, in a reasonably high dose of 800mcg a day, may reduce the risk of some cancers. It is cheap and side effects are very rare unless you take about five times this dose. Research some years ago suggested an even weaker effect for selenium. I am not advising anyone to take these supplements, merely pointing you to research. And glucosamine reduces painful joints.

There are prescription and non prescription drugs which can be used to prevent as opposed to treat illness – so call prophylaxis. Statins, used to treat high levels of cholesterol in the blood, play a major role in reducing heart attacks and strokes in the normal population. Sadly there has been some poor research and a group of doctors are opposed to routine drug administration in the population but I believe the evidence is clear that if you can take statins they are worth taking. Side effects are liver problems and muscle pain but these resolve if you then stop the tablets. Your GP should monitor your liver blood tests when you start.

Aspirin also reduces cardiovascular deaths but risks bleeding from the stomach which can be fatal. Research in the general population has been unclear as to whether the benefit outweighs the risk, so although you can buy aspirin over the counter I would strongly recommend you discuss this with your GP first. Interestingly it may also protect against bowel cancer but please talk to your GP!

Finally an interesting development – metformin. This incredibly cheap tablet is used to treat type 2 diabetes. A study following patients with diabetes found those on metformin had a lower incidence of heart attacks and strokes, although diabetes, which affects the small blood vessels, would be expected to increase the risk. Then a similar result was found for cancers. Metformin is known to work by inhibiting the mTORC1 pathway within cells which is responsible for cell proliferation in cancer.

A number of large studies are underway to confirm these exciting findings whilst other groups are looking at whether the drug may be helpful for dementia. It is too early to recommend widespread use as with statins, but we know metformin is safe in non diabetics – it cannot produce a hypo or low blood sugar and is commonly used for non diabetics such as women with polycystic ovaries. So certainly one to watch.

About the author

Dr Aubrey Bristow is a consultant anaesthetist in central London. These articles are his personal views and reflect individual issues of interest to patients. They are not a comprehensive review of the subject nor a substitute for a consultation with your anaesthetist.