A new randomized trial from the Vanderbilt-Ingram Cancer Center has shown that magnesium helps optimize vitamin D levels in the body[1][3]. In people with vitamin D deficiency, magnesium increased vitamin D levels, while in people with high levels it decreased them[1][3]. This study confirms a previous observational study from 2013 that linked low magnesium levels to low vitamin D levels[1][3]. The study included 250 people at risk of colorectal cancer due to risk factors or removal of a precancerous polyp[1][3]. Magnesium and placebo doses were adjusted according to initial dietary intake[1][3]. Magnesium deficiency blocks vitamin D synthesis and metabolism[1][3]. This explains why vitamin D supplementation does not work the same for everyone and why studies on its association with cancer or heart disease have yielded mixed results[1][3].