Low vitamin D levels negatively impact red blood cell production and may interfere with iron absorption, causing low iron levels. Low vitamin D levels can suppress the production of a hormone called hepcidin, which regulates iron absorption and iron concentration in the blood. Low iron stores may also contribute to low vitamin D levels by reducing the activity of iron-containing enzymes that activate vitamin D.This highlights the importance of monitoring vitamin D and iron levels, as low levels of one may negatively affect the other. Take vitamin D separately from some fat-soluble nutrients, like vitamin E, which competes for absorption with vitamin D.Though you can take vitamin D and iron together, it’s best to avoid taking iron with supplements that contain multiple nutrients, as some multivitamins that contain vitamin D also contain minerals that can reduce iron absorption. Additionally, if you’re severely low in vitamin D, you may require large doses of supplemental vitamin D or vitamin D injections.