Scientists have carried out a large number of studies to investigate whether vitamin D might help reduce or treat cancer. A large meta-analysis published in 2019 concluded that, although vitamin D did not reduce the incidence of cancer, it did reduce cancer mortality. Similarly, a large clinical trial published a year later found that although vitamin D supplementation was not linked with decreased cancer incidence, it was associated with a reduced incidence of advanced cancer.

Vitamin D and cancer

The term “natural” is fairly meaningless in relation to the safety or effectiveness of a supplement. To provide an extreme example, cyanide is a natural compound that ferns produce. Of course, we are not suggesting that any supplements contain cyanide.Some natural plant compounds do have medicinal properties, but there is more to it than that. For instance, dandelion roots are a laxative, whereas dandelion leaves are a diuretic.

If the label says ‘natural,’ it's not  always safe

Probiotics are foods or supplements that contain microorganisms, whereas prebiotics are foods or supplements that contain compounds designed to promote gut bacteria.In most instances, we still don’t know which probiotics are helpful and which are not. We also don’t know how much of the probiotic people would have to take or who would be most likely to benefit. Even for the conditions that have been studied the most, researchers are still working toward finding the answers to these questions.

Probiotics and prebiotics

Antioxidants are compounds that prevent oxidation, and they include vitamin C, vitamin E, selenium, and carotenoids, such as beta carotene. In general, fruits and vegetables are rich in antioxidants.Research has shown that people who eat more vegetables and fruits have lower risks of several diseases; however, it is not clear whether these results are related to the amount of antioxidants in vegetables and fruits, to other components of these foods, to other factors in people’s diets, or to other lifestyle choices

Antioxidants and longevity

In fact, more can sometimes be dangerous. As vitamin and mineral supplements are available without a prescription, people can be forgiven for assuming that they are safe at any dosage.Large dosages of some vitamins can hamper the body’s finely tuned systems. Too much vitamin C can interfere with the body’s ability to absorb copper, a metal that’s needed by the body. Too much phosphorous can inhibit the body’s absorption of calcium. The body cannot get rid of large doses of vitamins A, D, and K, and these can reach toxic levels when too much is taken.

More is not always better

Although there is a grain of truth to this slice of “common knowledge,” the evidence that vitamin C can prevent a cold is weak.The scientists found that vitamin C supplementation did not prevent the common cold in the general population. However, they did conclude that it reduced the severity of symptoms and the duration of the cold.

Vitamin C does not prevent a cold

The supplement industry is huge. In 2016, the global nutritional supplement sector turned over an estimated $132.8 billion. By 2022, some experts predict that this figure will exceed $220 billion.According to the National Health and Nutrition Examination Survey, in 2011–2012, 52%Trusted Source of adults in the United States reported using some kind of supplement. Almost 1 in 3 people (31%) took multivitamins.

Vitamins and supplements: the statistics

Many of these products contain active ingredients that might interfere with other drugs. Supplements might, therefore, boost or reduce the effects of pharmaceutical drugs.

Taking supplements alongside normal medicines

The idea that taking vitamin and mineral supplements will protect our hearts is reassuring. However, a large review and meta-analysis published in 2018 could find no significant benefit.

Vitamin and mineral supplements

In this edition of Medical Myths, we tackle some persistent myths about supplements, including multivitamins, probiotics, and antioxidants.