We invite you to contribute to a Special Issue of Nutrients, entitled Dietary Supplements . The purpose of this Special Issue is to advance dietary supplement science by presenting commissioned overviews on four nutrients of particular current interest and controversy: Vitamin D, iodine, iron, and omega-3 fatty acids. To supplement these contributions, we welcome the submission of manuscripts describing original research or providing systematic reviews related to various issues in dietary supplement science. Manuscripts across a broad range of topics will be considered, but we are particularly interested in manuscripts that address the following areas:

• Health effects, both positive and negative, of single nutrients, such as vitamin D, iodine, iron, and omega-3 fatty acids, with an emphasis on human studies.
  
• Human clinical trials of dietary supplement use
  
• Motivations for and prevalence of the use of dietary supplements
  
• Mechanisms of action of nutrients and other bioactive components of dietary supplements.
  
• Biomarkers of nutritional status, especially those measured in human samples.
  
• Development and application of analytical tools for the measurement of bioactive components of dietary supplements.
  
• Databases of dietary supplements’ composition for use in improving the assessment of nutrient intake and of the exposure to ingredients present in these products in human populations.