Are vitamin supplements really bad for your health? Professor Robert Thomas wades into the debate

This week, another scientific paper highlighted the potential harm a common ingredient found in many multi-vitamin supplements and fortified foods could cause, triggering a series of sensational headlines. This is not the first time, the health benefits of some vitamins and other ingredients has been put in question.

So, should we really be worried about the foods we eat or the supplements we take? - As a doctor and professor of nutrition, I explore the actual evidence.

This latest study reported an increased risk of a heart attack among people taking niacin (vitamin B3). Although potentially alarming, the risks have to be put into proportion and media articles featuring pictures of breakfast cereals are clearly out of proportion to the research findings.

Adding small amounts of niacin to food sources remains an important public health strategy. Deficiency of niacin was a major widespread cause of death until the early 20th century by a disease called pellagra, but fortification of flour and cereals has led practically to its eradication in developed countries.

Looking at the study in more detail, the authors reported that, in a group of 2000 men and women with known heart problems, those who took vitamin B3 had a higher incidence of subsequent serious cardiac events than those who did not.

The mechanism for this appears to be that a metabolite of unused vitamin B3 causes inflammation in the cardiac arteries - which could trigger a heart attack. The increased risk was, therefore, only seen in vulnerable people who take excess niacin, in supplement form, over long periods of time, so, fortified cereals and flour are extremely unlikely to have any negative influence.

That said, this study was still very relevant because many multi-vitamins have levels of niacin and other vitamins way-above the RDA (recommended daily allowance). In the light of these new findings, it would be sensible to read the label to ensure you don't exceed 100% RDA, especially if you have heart or blood pressure problems.

Reassuringly, most over the counter supplements are safe and can be a convenient way to avoid deficiency of specific nutrients essential for a healthy metabolism. A good example is Vitamin D which we would be deficient in, during the winter, without extra capsules or sprays. Likewise, there is evidence that giving B vitamins to heavy drinkers and vitamin C people in care homes with a poor appetite for fruit and vegetables are beneficial.

Supplements can also be useful way to boost intake of concentrated whole, phytochemical rich foods which have specific health properties such as turmeric and ginger for arthritis, phyto-v and yourgutplus for long covid, chamomile and resveratrol for sleep, Yourphyto for prostate and lutein for eyes, probiotics for gut health.

Most of these whole food supplement have a strong safety record, although it's best to choose blends which have undergone robust clinical evaluation. These would have had to be approved by ethical committees, have higher levels of quality assurance and hence safety.

Let's look at the pros and con of other commonly taken supplements.

Mineral supplements

These have a good safety record and suboptimal levels of essential minerals are becoming alarmingly commonplace. This is because in the race to get large quantities of affordable food, modern intensive farming, over cleaning and processing are depleting minerals from many foods on the shelves. Up to 75% of the worlds population now have suboptimal levels one of more essential trace minerals especially iodine.

Minerals are essential for the normal function of the body including the formation of protein, bone and cartilage, production of hormones, immune factors and anti-oxidants enzymes which protect us from toxins and chronic degenerative diseases such as dementia, heart disease, arthritis, cancer and premature skin ageing.

These are all good arguments for including a multimineral complex in your daily health routine but the trouble is, even with the hundreds of varieties of supplements available over the counter, it’s difficult to find one which contains the optimal blend. Many omit really import minerals such as iodine which is now worryingly deficient in the UK diet or have too many or inadequate quantities of other minerals. Look for one, such as Phytomineral, which has the complete range of essential minerals, including iodine at levels around 100% RDA and not more.

Vitamin A & E

Vitamin A deficiency still commonly effects children in developing countries causing blindness. In the west, however, vitamin A and E significant deficiencies are rare, but suboptimal levels should be avoided by eating a good diet of nuts, fruit, carrots, sweet potatoes.

Regular vitamin A and E supplements, unless correcting a known deficiency, should be avoided. Unlike natural phytochemicals from plants which promote a natural adaptive increase in anti-oxidant enzymes when needed, vitamin A and E are direct anti-oxidants and can actually override this process.

Vitamins A & E can also block signals which reduce the anti-oxidant enzyme levels when not needed. As such they cause anti-oxidant enzymes to remain elevated, even when the oxidative stress subsides. Combined with their direct antioxidant properties this can result in a state called anti-oxidative stress.

These biological process explain why studies have reported that excess intake of vitamin A and E reduces sports performance. For example, a study of kayakers found that those randomised to take a vitamin E and beta-carotene supplement had increased muscle damage and inflammation, hindering the recovery of muscle damage.

If taken for a long time they are also linked to an increased cancer risk. For example a study which gave vitamin A to smokers with the aim to reduce the risk of cancer actually found the incidence of lung cancer was higher. The Queensland skin cancer study also reported a higher rate of recurrent skin cancers in those taking vitamin E capsules. Likewise, the SELECT study showed a higher incidence of prostate cancer after vitamin E and the CARET Study showed an increased risk of both lung and prostate cancer.

Cloves and spearmint extracts

These contain especially high levels of a phytochemical called a polyphenol, which like vitamin E have been shown to overwhelm antioxidant pathways in laboratory studies. Most importantly, there is little research showing any benefits in humans and absolutely none involving men with prostate cancer.

Clove oil has been investigated as a euthanizing agent for fish species and spearmint has been investigated for hirsutism and could affect androgen levels in a negative way. This has not stopped some manufacturers, based on dubious research, adding them to untested blends and implying health benefits usually targeted at men.

Cod liver oil and fish oils supplements

Omega 3 and other fatty acids are essential for many vital biological pathways, yet western diets are noticeably deficient in them. We certainly should be eating more omega rich foods such as nuts, flax and chia seeds and avocados as well as seafood including mackerel, sardines and other oily fish.

A fish oil supplement, at first glance, seems a sensible way to boost intake but emerging studies have highlighted potential concerns. Some oils have been found by the consumer watchdog consumerlab.com to contain toxins including dioxins and PCB, as they use fish from polluted seas or fish that are higher up the food chain.

What's more, if exposed to heat, oxygen and light, fish oils are broken down into substances such as aldehydes which have carcinogenic properties - so if you do take fish oil supplements it's best to store them in a cool dark place and finish each batch well within the "use-by date".

Cod liver oil has particularly high levels of vitamin A, as well as naturally occurring vitamin E. Extra Vitamin E is also often added as a preservative. Clinical studies have reported that regular consumption probably does not help heart disease or stroke and in terms of cancer, may slightly increase prostate cancer risk although this more-likely relates to excess vitamin E intake.

The court is still out on whether these findings are significant and more research is needed but until this issue is resolved, many doctors would recommend avoiding fish oil supplements especially those with extra vitamin E. Instead concentrate on whole foods or omega rich supplements which have been sourced from non-animal sources such as algae.

General rules on taking vitamin supplements

Unlike drugs, over the counter supplements do not have medical licences so are not as strictly regulated by organisations such as the American FDA or the UK's MHRA. They are classed as foods but some health claims are permitted by the European Food Standards agency (EFSA) or in the UK, the Food Standards Agency (FSA).

You often see these allowed health claims on packaging of supplements include, for example, vitamin D supports healthy bones, Zinc supports the immune system, iodine support normal thyroid function and hormone formulation.

Try to look for supplements with appropriate health claims and, if possible, stick to those which have undergone formal clinical evaluation. It is, however, difficult for the public to spot these as many unscrupulous sellers add words such as "Research" in their company titles or description of their products in a ploy to mislead customers, despite conducting no clinical studies at all.

Many academic Institutes, including the one I currently lead, have conducted several studies on nutritional supplements and the ones involving concentrated whole foods rather than specific chemicals extracted from foods have the best evidence of benefit and the highest safety record.