In a research letter published on Monday in the Journal of the American Medical Association-Internal Medicine, scientists noted that they found that vitamin D pills that they prescribed during their studies often did not have the potency that the manufacturers had claimed. They also noted that the U.S. Food and Drug Administration does not regulate vitamins and other supplements, so "potency may not be well evaluated."
The researchers had become curious after testing vitamin D supplements that were being given to women participating in a study regarding the supplements' efficacy when used during menopause. The amount of variance in the prescribed pills, according to their research letter, led them to begin testing over-the-counter varieties as well.
Here is some of the key information that was released on Monday regarding this study into vitamin D supplements.
* Overall, researchers say that they discovered that only one-third of the pills that they were giving to women in their initial trial met U.S. standards for potency.
* U.S. standards are determined by the the U.S. Pharmacopeial Convention, and state that compounded pills, such as the ones that were being used in the initial trial, must contain between 90 percent and 110 percent of the active ingredient listed on the label.
* Dr. Erin LeBlanc , who is one of the authors of the study and an endocrinologist at the Kaiser Permanente Center for Health Research in Portland, Ore., told the media on Monday that her team found that "the potency of these vitamin D supplements varied widely," as quoted by USA Today.
* The amount of actual vitamin D in any one of the supplements that the team tested ended up being between 9 percent and 140 percent of the actual amount listed on the packaging.
* When five pills were tested and the results averaged together, the results often were closer to being 100 percent of the promised dosage, but individual pills may contain too much or too little of the supplement to be effective.
* LeBlanc and her team found that even the pills that they were using in their initial trial, which were prescription strength and had been compounded, often contained between 52 percent and 146 percent of the vitamin D promised on the packaging.
* The concern, according to the team, is that those taking over-the-counter vitamin D supplements to treat a known deficiency may not get enough of it to actually help if the pills do not contain the amount of the supplement that is claimed on the labels.
* LeBlanc noted herself on Monday that if people with a known deficiency "are consistently taking a supplement with little vitamin D in it, they could face health risks," as quoted by MyHealthNewsDaily.
Vanessa Evans is a musician and freelance writer based in Michigan, with a lifelong interest in health and nutrition issues.