Vitamin supplements: helpful or harmful?

Dr Hannah Sweilam

We spend more than £420 million a year on vitamin supplements that are supposed to improve our health, but are they really helping? Dr Hannah Sweillam investigates.

Recent years have seen an increase in the use of vitamin supplements and now as many as two thirds of adults (65%) take some form of vitamin or supplement.  There’s no denying that vitamin deficiency can lead to illness and that in these circumstances, vitamin supplements can be beneficial. The real question, though, is whether vitamin supplements are of any benefit to healthy individuals?

There seems to be a perception among the general population that vitamin supplements as a whole guard against chronic disease, and a tendency to accept them as ‘natural products’ that are beneficial and safe, even if they have not been proven to be so.  Yet a growing body of evidence suggests that multivitamins offer little or nothing in the way of health benefits, and that certain vitamins might cause harm. Lets take a look at some of the most popular.


 Multivitamins: multi-risks?

Multivitamins are the most popular type of supplement and 46% of all adults have taken multivitamins in the last 12 months according to research by Mintel, a marketing research agency. The origin of this trend is not clear but one thing’s for sure: it wasn’t started by medical doctors.

In 2011, researchers from the University of Minnesota evaluated over 38,000 older women and found that those who took supplemental multivitamins, magnesium, zinc, copper, and iron died at rates higher than those who didn’t. The researchers commented, “Based on existing evidence, we see little justification for the general and widespread use of dietary supplements”, and concluded they would prefer supplements to be used only for medically-defined reasons, such as a proven nutrient deficiency.




In 2004, the Lancet published a review of 14 studies which evaluated the effect of multivitamins on cancers (throat, stomach, bowel, pancreatic and liver cancer). The multivitamins were comprised of beta-carotene, vitamins A, C, E, and selenium, all of which are antioxidants. It is reasonable to think that antioxidant supplements might have a positive effect on health as oxidation in the body (the process that converts food to energy) produces free radicals, which are thought to play a part in the development of many diseases, including cancer.  Turns out, it’s not that simple. The results indicated that these supplements did not help prevent gastrointestinal cancers and instead, the researchers concluded that “they seem to increase overall mortality” or death rates.  A separate study, which looked at whether a similar concoction of antioxidants could reduce the risk of skin cancer, found that these vitamins appeared to increase the risk of skin cancer in women.

Two trials found a small (only borderline) significant benefit from multivitamin supplements on cancer in men, and out of these studies, the one that included women found no benefit to women.  On the subject of whether multivitamins can help stave off dementia, a study published in the American Journal, Annals of Internal Medicine in 2013, concluded that multivitamins don’t help to prevent memory loss.


What about single vitamin supplements?


Can single vitamin supplements beneficial? The short answer: if you’re a healthy adult, probably not

Vitamin A

There is evidence from observational studies that people who eat more fruit and vegetables, which are rich in vitamin A, and people who have higher blood levels of beta-carotene (a vitamin A precursor), have lower rates of lung cancer.  On the back of this, a study researched the effect of a daily vitamin A  supplement on more than 18,000 people who were at high risk of developing lung cancer.  The study had to be stopped early because of clear evidence of no benefit of vitamin A supplements and mounting evidence of possible harm: there were 28% more lung cancers and 17% more deaths among those taking the supplement.

Similarly, the Cancer Prevention Study, of more than 29,000 male smokers in Finland, found that vitamin A supplements did not reduce the risk of cancer and that there were more deaths (from lung cancer and heart disease) among those taking the supplements.



Vitamin E

In 2005, researchers evaluated 19 trials, involving more than 135,000 participants who took vitamin E supplements.  The study found an increased risk of death associated with high-dose (more than 400 IU) vitamin E supplements and concluded that they should be avoided.  It’s easy to buy vitamin E capsules, in stores or online, that contain a dose as high as 1000 IU. That same year, another study published in the Journal of the American Medical Association, studied people with diabetes or vascular diseases who took vitamin E; those who took vitamin E were more likely to develop heart failure than those who didn’t.  An international network of research institutions found that men who took vitamin E had an increased risk of prostate cancer.


A link between calcium supplements and an increased risk of heart problems is a recurring theme in research papers.  A trial that looked at data from 23,980 participants aged 35 to 64 years concluded that calcium supplements might increase the risk of heart attacks and “should be taken with caution”.

One large Swedish study of more than 60,000 women investigated the association between long-term intake of calcium supplements and death. It found that high intakes of calcium were associated with higher death rates from all causes and a higher risk of cardiovascular disease (disease relating to the heart and blood vessels).   An American study, involving more than 388,000 participants, found that a high intake of supplemental calcium is associated with an increased risk of cardiovascular death in men, but not in women.

So does that mean you should throw your calcium tablets in the bin? It depends on your age. In certain cases, particularly in the older population, calcium supplements are important in helping to prevent osteoporosis and it’s not suggested that calcium supplements should be avoided all together. Rather that they should be taken only when there is an identified medical need and in accordance with medical advice.



Clear role for vitamin supplements in specific situations

 Certain vitamin supplements, in cases of a clearly defined medical need, are still recommended.  For example, use of folic acid by pregnant women to prevent birth defects, is definitely recommended.  Likewise, a very clear role exists for other dietary supplements, such as iron supplements to treat anaemia, and in certain cases vitamin D and calcium supplements play an important role in bone health.


The bottom line

Vitamin supplements can be either helpful or potentially harmful depending on the situation.  In particular cases they are helpful and will be recommended by a medical professional.

On the other hand, convincing evidence of any real health benefit from multivitamins is lacking and certain vitamin supplements have been associated with an increased risk of heart problems, cancer and death.

There is still a lot we don’t understand about vitamins and how they interact with our body.  It’s possible, for example, that some vitamin supplements are not processed by our body the same way that vitamins found naturally in our diet are, and that exceeding the recommended daily amount of certain vitamins (which is difficult to do through diet alone) could be more harmful than people realise.

The best approach is have a balanced, healthy diet and to use supplements with caution- only where there is a defined medical need and in accordance with medical advice.