The new analysis, published in the journal Nutrients, noted that many research projects have attempted to study nutrients that are naturally available in the human diet the same way they would a powerful prescription drug.
As such many of these studies have come to conclusions that have little scientific meaning, even less accuracy and often defy a wealth of other evidence, according to Professor Balz Frei of the Linus Pauling Institute at Oregon State University - who led the new study.
Such flawed findings will continue until the approach to studying micronutrients is changed, he added - noting that changes are needed to provide better, more scientifically valid information to consumers around the world who often have poor diets, do not meet intake recommendations for many vitamins and minerals, and might greatly benefit from something as simple as a daily multivitamin or mineral supplement.
"One of the obvious problems is that most large, clinical studies of vitamins have been done with groups such as doctors and nurses who are educated, informed, able to afford healthy food and routinely have better dietary standards than the public as a whole," explained Frei - who is an expert on vitamin C.
"If a person already has adequate amounts of a particular vitamin or nutrient, then a supplement will probably provide little or no benefit," he said. "That's common sense."
"But most of our supposedly scientific studies take results from people with good diets and healthy lifestyles and use them to conclude that supplements are of no value to anyone."
The new analysis specifically looked at problems with the historic study of vitamin C, however the scientists behind the analysis said many of their observations are more broadly relevant to a wide range of vitamins, micro nutrients and studies.
Frei and his colleagues argued that nutrition research requires new methodologies that accurately measure baseline nutrient levels, provide supplements or dietary changes only to subjects who clearly are inadequate or deficient, and then study the resulting changes in their health.
Indeed, the team noted that supplementation or an improved diet will primarily benefit people who are inadequate or deficient to begin with. However, most modern clinical studies do not perform a baseline analysis to identify nutritional inadequacies and do not assess whether supplements have remedied those inadequacies.
As a result, any clinical conclusion made with such methodology is pretty much useless, they said - adding that tests must be done with blood plasma or other measurements to verify that the intervention improved the subjects' micronutrient status along with biomarkers of health.
In addition, Frei and his colleagues noted that new approaches are required to better reflect the different ways in which nutrients behave in cell cultures, lab animals and the human body.
"In cell culture experiments that are commonly done in a high oxygen environment, vitamin C is unstable and can actually appear harmful," explained Alexander Michels, a lead author on the report. "And almost every animal in the world, unlike humans, is able to synthesize its own vitamin C and doesn't need to obtain it in the diet. That makes it difficult to do any lab animal tests with this vitamin that are relevant to humans."
Indeed, many studies have found that higher levels of vitamin C intake are associated with a reduced incidence of chronic disease, including coronary heart disease, stroke, diabetes, hypertension and some types of cancer. The levels of vitamins needed for optimal health also go beyond those needed to merely prevent deficiency diseases, such as scurvy or rickets, they added.
Volume 5, Number 12, Pages 5161-5192; doi:10.3390/nu5125161
"Myths, Artifacts, and Fatal Flaws: Identifying Limitations and Opportunities in Vitamin C Research"
Authors: Alexander J. Michels and Balz Frei