Study after study has shown that vitamin supplements do not offer any benefits over a well-balanced diet. In certain cases they may even be detrimental to health. In 1994, the National Cancer Institute, showed, after studying 29,000 Finnish men, all long-term smokers, that those receiving beta carotene supplements had an 18% increased risk of developing lung cancer. Two years later another study in the U.S. involving 18,000 subjects at risk indicated that those taking vitamin A and beta carotene had a 28% increased risk of developing lung cancer. The same pattern has been repeating itself since then. For instance, studies in 2004 have shown that antioxidants such as vitamin A, C, E and beta carotene not only do not prevent cancer but appear to increase overall mortality. With vitamin E a further issue has arisen. Researchers from the Cleveland Clinic studied 36,000 men and found that those taking vitamin E had a 17 percent greater risk of developing prostate cancer.
Still vitamin D seemed to be the exception, and until recently continued to be promoted for the prevention of cancer, cardiovascular disease and other conditions. The problem was that these recommendations were mostly based on observational studies. In this type of study researchers follow a group of people to determine what factors may affect their health. But it is very difficult to draw conclusions from observational studies. It might be that people taking vitamin D are healthier, not because of the vitamin, but possibly because they have also a better diet or they exercise more. More conclusive data are based on randomized control trials. This involves following two groups of people, one group given vitamin D and the other a placebo, and looking for the outcome. In meta-analyses, studies are combined to increase the size of the pool and therefore reliability.
This is the approach followed by a group of New Zealand researchers. In “The Lancet Diabetes and Endocrinology (January 24, 2014),” they reported on meta-analyses of randomized controlled trials on skeletal, vascular and cancer outcomes associated with vitamin D supplementation. This involved examining 38 different trials with a total of over 80,000 different subjects.
The conclusion represents another setback for those who promote the routine use of vitamin supplements. There is little justification for prescribing vitamin D supplements in the general population to prevent cardiovascular disease, cancer, fracture, or to reduce the risk of death. Unfortunately I am not sure that the study will have an impact on supplement sales which in North America amount to more than $ 30 billion a year.