Some recent clinical trials have concluded that vitamin supplements are of no value or they may even be harmful. (Agencies)
Many projects have tried to study nutrients that are naturally available in the human diet the same way they would a powerful prescription drug, researchers said.
This leads to conclusions that have little scientific meaning, even less accuracy and often defy a wealth of other evidence, said Balz Frei, professor and director of the Linus Pauling Institute at Oregon State University.
These flawed findings will persist until the approach to studying micronutrients is changed, Frei said.
New methodologies are needed 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, researchers said.
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, they said.
And other approaches are also needed that better reflect the different ways in which nutrients behave in cell cultures, lab animals and the human body.
The analysis specifically looked at problems with the historic study of vitamin C, but scientists say many of the observations are more broadly relevant to a wide range of vitamins, micro nutrients and studies.
"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," said Frei, an international expert on vitamin C and antioxidants.
Vitamin or mineral supplements, or an improved diet, will primarily benefit people who are inadequate or deficient to begin with, researchers said. But most modern clinical studies do not do 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.
"It's fine to tell people to eat better, but it's foolish to suggest that a multivitamin which costs a nickel a day is a bad idea," researchers said.
Many scientists studying these topics are unaware of ways in which nutrients may behave differently in something like a cell culture or lab animal, compared to the human body.
This raises special challenges with vitamin C research in particular, researchers said. The research review was published in the journal Nutrients.
Some recent clinical trials have concluded that vitamin supplements are of no value or they may even be harmful.