Daniel Sereni, France
A large proportion of adults in western countries regularly take vitamins supplements. This represents a huge market. But is it useful?
It is well established that vitamins are essential for our health. Vitamin deficiencies provoke diseases and foetal and developmental abnormalities. Children are receiving vitamin D supplements for Ricketts prevention and some elderly people need vitamin D because of proven deficiency. There are indications for folic acid (a group B vitamin) supplementation during pregnancy in defined situations.
Vitamin deficiency may result from insufficient intake or absorption, and this can lead to serious complications. Deficiency has also to be prevented or corrected in some diseases (for example intestinal or liver disease) or when people are given certain treatments that interfere with the absorption or the metabolism of vitamins.
But millions of people without any recognised or suspected deficiency take vitamins every day (usually “multivitamins“). They do so because some medical publications have suggested that vitamin supplements can prevent major and frequent illnesses like cardio-vascular disease and cancer.
Most of these assumptions were based on observational studies. There have been also a few randomised clinical trials comparing the outcome of people receiving a vitamin supplement compared to a group receiving a placebo.
The US Preventive Task Force (USPTF), a recognized independent organisation, has recently published a recommendation based on a systematic review of the 87 published randomised trials evaluating vitamin supplementation in the prevention of disease in healthy adults. The USPTF concludes that current evidence is insufficient to assess the balance of benefits and harms of the use of multivitamin supplements for the prevention of either cardiovascular disease or cancer.
There is thus no evidence that vitamin supplementation in healthy adults prevents cardiovascular diseases and cancer. Actually, there are adverse effects due to vitamin excessive intake, such as an increased risk of kidney stones, fractures, and stroke. These adverse effects are rare, but they show that systematic vitamin supplementation is not only useless but may be harmful.
