On 17 July 2012, Euromonitor International published a blog by consumer health analyst Stephanie Prymas titled:’ Vitamins and Dietary Supplements: Too Much of a Good Thing?’. The blog states: “Unfortunately, there is a growing body of evidence showing that overdoing it on certain nutrients can indeed be harmful.”
The seven statements and the studies they refer to, provide very weak support for the statement regarding growing evidence showing that overdoing it on certain nutrients can be harmful. The findings of two of the studies cannot be extrapolated to Europe. The other studies have been criticised by experts because of their methodological limitations and because they cite relative risk figures which do not reflect actual risks.
Below, I respond to each of Stephanie’s seven statements.
Statement (1): “A study in the November 2011 American Journal of Clinical Nutrition, which surveyed nearly 9,000 US adults, found that supplement users consume more minerals from their diets than non-users, increasing the risk of conditions such as kidney stones, which are associated with high calcium consumption.”
It is important to highlight the fact that this statement relates to an analysis of data from the National Health and Nutrition Examination Survey (NHANES) 2003-2006 in the United States. NHANES is a program of studies designed to assess the health and nutritional status of adults and children in the United States. Its findings and conclusions cannot be extrapolated to other national populations. One of the main reasons for this is the fact that the use of dietary supplements is very high in the United States compared to other countries.
The actual conclusions cited in the abstract of the November 2011 American Journal of Clinical Nutrition analysis were: “Individuals who used mineral-containing dietary supplements had higher mineral intakes from food sources in the diet than did nonusers. For all minerals examined, and particularly for calcium and magnesium in men and women and iron in women, supplement use decreased the prevalence of intake inadequacy for each respective mineral.”
Statement (2): “Researchers followed almost 24,000 subjects in Germany for 10 years and discovered that those taking calcium supplements were 86% more likely to have a heart attack during the study. While this relationship was not causal, the association was strong enough to prompt the authors to suggest that dietary consumption may be a preferable calcium source.”
Dr William Ware, Editor of International Health News has noted that this study received considerable media attention because it suggested an 86% increase in the risk of having a heart attack for users of calcium supplements.
However, from looking at the data in the tables of the study write-up and focusing on myocardial infarctions (heart attacks), he notes that over 11 years, 1.6% of non-takers of any supplement had heart attacks. 2.73% of those who took only calcium had heart attacks and 1.87% of those who took calcium plus another supplement had heart attacks.
Dr Ware notes that the 86% relative risk increase for calcium alone became a non-significant 20% when the statistical analysis involved confounders and in addition, took into account cumulative supplementation.
The International Alliance of Dietary/Food Supplement Associations (IADSA) highlighted a large number of limitations of the observational study including that it was not designed to measure CVD (cardiovascular disease) events as the primary outcome; didn’t exclude those with high blood cholesterol and high blood pressure; and contained inaccurate calcium intake data.
Statement (3): “Patients with excess levels of vitamin D have a 2.5 times greater risk of developing atrial fibrillation…”
The research cited resulted in an article titled “Industry hits back at ‘nonsense’ vitamin D heart study” which appeared on the NutraIngredients website on 18 November 2011. The article cited a statement by supplier DSM which was headlined ‘Conversion Errors and Vitamin D Nonsense’. According to the article, DSM stated that the unpublished research was flawed in its measurement methodology and would struggle to pass peer review.
Statement (4): “Researchers at Johns Hopkins University analysed data from more than 15,000 adults and found that vitamin D supplementation decreased blood levels of C-reactive protein, or CRP, an indicator of inflammation linked to cardiovascular disease. After a certain level, however, additional vitamin D actually increased CRP levels. Most troublingly, this threshold was at the lower end of the “normal” range for vitamin D.”
The Vitamin D Council said of this study: “You can’t draw any conclusions about CVD (cardiovascular disease) risk because this was a correlation of two serum levels between two unmatched groups. It was not an intervention study, and it did not measure CVD.”
Statement (5): “Dutch researchers examined over 245,000 people and found both low and very high levels of vitamin D were linked to a greater risk of death.”
Firstly, this study was not carried out by Dutch researchers! The research was from the University of Copenhagen and was based on blood samples from 247,574 Copenhageners. Commenting on the finding of the study on the Vitamin D Council website, Dr William Grant stated: “This finding flies in the face of numerous studies reporting benefits of higher serum 25(OH)D concentrations for the diseases contributing the most to mortality rates in Europe and the United States.”
Statement (6): “A study of more than 35,000 men in the October 2011 Journal of the American Medical Association found that those taking vitamin E had a 17% higher risk of developing prostate cancer versus those receiving a placebo.”
This study reported that those taking vitamin E had a 17% higher risk of developing prostate cancer versus those receiving a placebo. This was a relative risk. Relative risk means the probability of developing a disease relative to an exposure, while absolute risk represents the probability that a specific event will occur in a specific population, in a specific time frame.
Statement (7): “According to a study in The Lancet in February 2012, selenium supplements, which may prevent some cancers and delay cognitive decline, may also increase the risk of developing Type 2 diabetes when taken at higher doses.”
The main conclusion of this review of the evidence was that although additional selenium might benefit people who are lacking in this essential micronutrient, for those who already have enough selenium in their diet (including a large proportion of the USA population), taking selenium supplements could be harmful, and might increase the risk of developing type-2 diabetes
However, it should also be noted that the intake of selenium varies hugely worldwide. Whilst intakes are high in the USA, Canada and Japan, they are lower in Europe. The Review found that studies in different populations with different selenium status and genetic background have produced divergent results.