Doctors have known for a long time that people who are sick often have very low blood levels of vitamin D. This naturally led to the assumption that taking vitamin D supplements might help fight disease.

In a recent paper, however, Trevor Marshall, Ph.D., professor at Australia's Murdoch University School of Biological Medicine and Biotechnology, argues that this assumption is wrong.

... Supplemental vitamin D has been used for decades, and yet the epidemics of chronic disease, such as heart disease and obesity, are just getting worse.

Marshall explains that our bodies contain something called a Vitamin D Nuclear Receptor (VDR), which plays a key role in our immune response to cancers, multiple sclerosis and other diseases. The VDR lowers vitamin D levels as a normal part of our body's response to disease. In other words, low levels of vitamin D in sick people are a sign that the immune system is doing its job.

"Molecular biology is now forcing us to re−think the idea that a low measured value of vitamin D means we simply must add more to our diet," Marshall says, "Supplemental vitamin D has been used for decades, and yet the epidemics of chronic disease, such as heart disease and obesity, are just getting worse. In fact, the use of supplements can be harmful, because they suppress the immune system so that the body cannot fight disease and infection effectively."

Published in the current issue of the journal BioEssays, Marshall's research shows that even small doses of ingested vitamin D can interfere with the proper operation of the immune system.