The results of the new research suggest that people who consume too many dietary supplements of the mineral may put themselves at risk of heart infection.
Manganese is an essential mineral that, if consumed excessively, can be toxic. The mineral can be found in abundance in leafy vegetables such as spinach and kale, as well as in tea, pineapple, and nuts.
A new study published in the journal Cell Host & Microbe suggests that excessive dietary manganese may even lead to a fatal infection of the heart. The infection in question is caused by the bacterium Staphylococcus aureus, which is also known as "staph" or "golden staph."
Staph is also the leading cause of infective, or bacterial, endocarditis. This occurs when S. aureus, having entered the bloodstream, is carried to the heart and settles in a heart valve or in the inner lining of the heart chamber.
The senior author of the new study is Eric Skaar, Ph.D., who is the Ernest W. Goodpasture Professor of Pathology, Microbiology, and Immunology at the Vanderbilt University Medical Center in Nashville, TN.
Manganese may lead to heart infection
Prof. Skaar told Medical News Today that he and his colleagues analyzed "the impact of multiple metal deficiencies and excess on S. aureus infection" in mice.
They fed a group of mice three times more manganese than the normal amount, and another group of mice was fed a normal diet. The team found that "only excess manganese had an effect on susceptibility to infection."
Most of the mice that received excessive manganese died as a result of a staph infection.
"We were surprised because we expected metal deficiency to impact susceptibility, not metal excess," Prof. Skaar told us.
The researchers put forth an explanatory mechanism for their findings, which involves the immune system's so-called reactive oxygen burst - also known as oxidative, or respiratory, burst.
Oxidative burst is a key process of the body's innate ability to defend itself against bacteria. During it, reactive oxygen species, or oxygen-containing molecules, are rapidly released by different types of immune cell.
Prof. Skaar explains that in the case of a staph infection, under normal conditions, "neutrophils [a type of white blood cell] pour into the site of infection and blast the bacteria with reactive oxygen species."
However, excessive manganese seems to counteract this process. A protein key for absorbing excess manganese and other metals seemed to be inactive in the hearts of mice fed too much manganese.
This protein is called calprotectin. It is part of the immune system's antimicrobial line of defense, and its role is to keep bacteria away from nutrients, inhibiting their growth.
Clinical implications of the findings
"[In our study] we are using a level of metal that could reasonably be encountered by humans, and some patient populations who are at increased risk for S. aureus infection are exposed to comparable levels of manganese," Prof. Skaar explained to MNT.
He notes that these patients who are more likely to get a staph infection and develop endocarditis have also been found to have abnormally high levels of tissue manganese in previous studies.
These people include substance abusers who inject drugs intravenously, people with liver disorders, and patients who have been on an intravenous diet for a long time.
"It's striking that a single dietary change can inactivate one of the most powerful branches of innate immune defense and lead to fatal infection," Prof. Skaar said.
In the future, he and his team plan to examine in more depth why the heart, in particular, is prone to fatal staph infections.
"The human body does a wonderful job of regulating nutrient levels, and a traditional Western diet has plenty of minerals in it. The idea of super-dosing nutrients needs to be given careful consideration."
Prof. Eric Skaar