Most clinical studies of vitamins are "flawed by poor methodology", review finds
Most large clinical trials of vitamin supplements, including those that have concluded supplements are of no value or even harmful, have a “flawed methodology” that renders them “largely useless” in determining the real value of these micronutrients, a new analysis from Oregon State University has suggested.
Many projects have tried to study nutrients that are naturally available in the human diet in the same way they would a powerful prescription drug, according to the authors of the analysis, which was published on 16 December 2013 in the journal Nutrients. They said this leads to conclusions that have “little scientific meaning, even less accuracy and often defy a wealth of other evidence”.
New approach needed
The authors said the “flawed findings will persist until the approach to studying micronutrients is changed”. Such 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 a daily supplement, according to the authors.
New methodologies are needed that accurately measure baseline nutrient levels, provide supplements or dietary changes only to subjects who are clearly inadequate or deficient, and then study the resulting changes in their health, the authors 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. The authors also said 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 new analysis specifically looked at problems with the historic study of Vitamin C, but the researchers said many of the observations are more broadly relevant to a wide range of vitamins, micronutrients and their relevant 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 Balz Frei, and international expert on Vitamin C and antioxidants, and Professor and Director of the Linus Pauling Institute (LPI) at Oregon State University.
“If a person already has adequate amounts of a particular vitamin or nutrient, then a supplement will probably provide little or no benefit,” Professor Frei 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,” he said.
The researchers said vitamin or mineral supplements, or an improved diet, will primarily benefit people who are inadequate or deficient to begin with. But their analysis found that most modern clinical studies did not do baseline analysis to identify nutritional inadequacies and did not assess whether supplements had remedied those inadequacies.
Many people do not have an ‘optimal diet’
An optimal diet, rich in fruits and vegetables, can provide most of the nutrients needed for good health, which supplement critics say is reason enough not to use them. But the authors of the analysis said this criticism missed a “pretty obvious” point — that many people do not have an optimal diet.
“More than 90 percent of U.S. adults don’t get the required amounts of vitamins D and E for basic health,” Professor Frei said. “More than 40 percent don’t get enough vitamin C, and half aren’t getting enough vitamin A, calcium and magnesium. Smokers, the elderly, people who are obese, ill or injured often have elevated needs for vitamins and minerals,” he said.
“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,” Professor Frei said.
Nutrients behave differently in different environments
Beyond that, the authors of the analysis 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.
“In cell culture experiments that are commonly done in a high oxygen environment, vitamin C is unstable and can actually appear harmful,” said Alexander Michels, an LPI Research Associate and lead author on this 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,” he said.
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 merely to prevent deficiency diseases, such as scurvy or rickets.
Even though such studies often significantly understate the value of dietary supplements, the authors of this analysis said the largest and longest clinical trial of multivitamin/mineral supplements found a total reduction of cancer and cataract incidence in male physicians over the age of 50. That study suggested that if every adult in the US took such supplements, it could prevent up to 130,000 cases of cancer each year.
“The cancer reduction would be in addition to providing good basic health by supporting normal function of the body, metabolism and growth,” Professor Frei said. “If there’s any drug out there that can do all this, it would be considered unethical to withhold it from the general public. But that’s basically the same as recommending against multivitamin/mineral supplements,” he said.
Australian Food News reported earlier in January 2014 that a study in Norway had found that dietary supplements may be harmful to the body’s own defense systems.