20 August 2012
15 August 2012
The Harvard School of Public Health, Boston, USA
“Scientific research is very complex. There are many different types of research studies, and each has its distinct strengths and weaknesses. Studies can provide established relationships (evidence) as well as probable and possible links, for example, between nutrient intake and disease risk reduction. Nutritional science has adopted the rules of evidence-based medicine, considering randomized, placebo-controlled trials (RCTs) as the best providers of scientific evidence as they infer strong causal relationships. However, experts criticize that as the criteria of evidence-based medicine do not fit into a nutritional context, the effects of nutrients and dietary supplements cannot be measured like those of the drugs in evidence-based medicine (see also Looking for evidence in nutritional science and What insights can be expected from micronutrient supplementation studies?). Consequently, meta-analyses using RCTs can be of limited validity, particularly when they have questionable inclusion criteria for studies, disregard certain trials, and compare studies that are not really comparable (see also Do antioxidant supplements increase mortality? and Analyzing the Benefit/Risk Ratio of Antioxidant Supplements).
One of the most crucial things to keep in mind is how a given study referred to in the mass media fits into the entire body of evidence on a topic.
The starting point for many (if not all) mass media reports on supplements is that the major vitamin trials have, for the most part, produced disappointing results, and even evidence of harmful effects in some cases. Scientific research is, however, much too complex to be properly discussed in a balanced way in simple newspaper articles. The majority of the most popular studies used by the media to produce stories about harmful effects of micronutrient supplements do not provide conclusive, generalizable information:
Some famous examples of such trials are two studies from the 1990s which suggested that high doses of beta-carotene (10 times the recommended dose) taken for years by heavy smokers and asbestos workers increased their risk of lung cancer (1,2). Not all trials of beta-carotene have showed this harmful effect. However, many newspapers turned this into a general warning against supplements containing beta-caro-tene, disregarding the fact that potential harmful effects were shown in groups at a high-risk of lung cancer taking excessive doses. Sometimes, the media even present positive results in a uniformly negative way. The SU.VI.MAX trial (3), for example, showed a reduction in cancer risk by 31% and overall mortality by 37% among men taking a combination of antioxidant vitamins and minerals. These effects were not apparent in women, because they (unlike with the men) tended to already have sufficient blood concentrations of the nutrients at the beginning of the study. Typically, media reports only mention that there was no effect in women – and so the study is mostly represented in a negative fashion.
Although many mass media reports are written in a one-sided and simplistic way, some of the points in the negative statements about dietary supplements are valid: ideally, a balanced and varied diet should cover micronutrient requirements. Dietary supplements can close gaps in nutrient intake but they cannot compen-sate for a generally unhealthy lifestyle. Regarding supplement dosage, consumers should follow the nutrient intake recommendations of public health authorities.”
Based on: Harvard School of Public Health. The Nutrition Source – Nutrition Research and Mass Media: An Introduction. Published online 2012.
20 August 2012
30 October 2012
The US Institute of Medicine has published new data advising that almost all people take sufficient vitamin D when their blood levels are at or above 20 nanograms per milliliter. Other scientists continue to endorse the older guidelines recommending vitamin D levels above 30 nanograms per milliliter.
6 September 2013
A new study from India suggests that anti-inflammatory effects of vitamin D may contribute to the treatment of gingivitis, an inflammation of the gum tissue.