Complex sentence: The U.S. National Institutes of Health notes that none of these products are intended for the prevention or treatment of any disease and in some circumstances supplements are dangerous; adding that certain supplements "may have value" for those who fail to consume a balanced diet.
Split into simpler sentences: The U.S. National Institutes of Health notes supplements aren't intended to prevent or treat any disease and in some circumstances supplements are dangerous. The agency says certain supplements "may have value" for those who fail to consume a balanced diet.