ORONO – An apple a day may be a simple recommendation for healthy eating, but when it comes to trace elements in the diet, the guidelines get a little more complicated.

So it is with manganese, an element that is critical, as a team of University of Maine researchers is finding, for cardiovascular health.

The federal government has not developed daily recommended intake levels for manganese as it has for other nutrients such as vitamin C and calcium. However, the importance of manganese in the diet is becoming clearer. In 1998, a research team led by Dorothy Klimis-Zacas of the University of Maine Department of Food Science and Human Nutrition reported evidence that the trace element may be important to biochemical processes in artery walls.

Now, she and her students have turned to mechanical tests of arteries to determine if indeed a lack of manganese paves the way for heart disease.

“Manganese is critical for synthesis of GAGs, the cement of the artery, that make the arterial walls strong,” said Klimis-Zacas. “We know that manganese deficiency leads to lower production of GAGs in arteries. Now we want to see if it also leads to functional changes in how well arteries work.

Members of the research team include Anastasia Kalea, a student from Greece; Cindy Norton, a student from Whiting; and Matt L’Italien, an undergraduate student from Jay. Their work is supported by a $70,206 grant from the U.S. Department of Agriculture.

The project got under way in June when the team began feeding 60 laboratory rats with diets that had three levels of manganese but were otherwise identical.

In another aspect of the study, blueberries are being studied to see if they have any effect on the mechanical properties of arteries. Since blueberries are high in antioxidants and manganese, the research team wants to see if adding the fruit would confer protection to the arteries from damages related to the low manganese diet.

After 15 weeks, the researchers surgically removed the threadlike arteries from the rats. Using a unique and sensitive system, they fastened one end of the arteries to a device that records maximal force developed by the artery and stores data in the computer. The rest of the artery is suspended in a solution. The researchers then tested the ability of each artery to contact and relax when exposed to two stimulants, epinephrine and acetylcholine.

The results, which will be reported next spring at the Annual Meeting of Experimental Biology in New Orleans, could underscore the importance of dietary manganese in maintaining the health of artery walls. The American Heart Association estimates more than 60 million Americans have one or more forms of cardiovascular disease including high blood pressure and coronary heart disease.

“For cardiovascular disease, manganese deficiency could just be the beginning. It appears to prepare the artery for another insult. That could be caused by oxidized cholesterol or tobacco smoke,” said Klimis-Zacas.

Klimis-Zacas is the editor of “Manganese in Health and Disease,” a book published by CRC Press in 1994 and is preparing the second edition of Nutritional Concerns for Women by CRC to be published in 2003.