Vitamin D levels can be optimized by Magnesium. Lower vitamin D levels may be caused by magnesium deficiency. Dr. Martha Shrubsole writes “Vitamin D insufficiency is something that has been recognized as a potential health problem on a fairly large scale in the United States… A lot of people have received recommendations from their healthcare providers to take vitamin D supplements to increase their levels based upon their blood tests. In addition to vitamin D, however, magnesium deficiency is an under-recognized issue. Up to 80% of people do not consume enough magnesium in a day to meet the recommended dietary allowance (RDA) based on those national estimates.”
Source - American Journal of Clinical Nutrition in 2018.