New research may help explain why eating fruits, vegetables, whole grains, and nuts helps protect the heart and prevent diabetes.

The key may be the mineral magnesium.

People in the study who ate magnesium-rich diets seemed to be protected against developing metabolic syndrome, a cluster of risk factors linked to cardiovascular disease and diabetes.

These risk factors include elevated blood pressure, low levels of HDL "good" cholesterol, elevated triglycerides (blood fats), elevated fasting-glucose (blood sugar) levels, and abdominal obesity as determined by waistline measurement.

Low-Magnesium Diets

Study participants who ate diets low in magnesium were more likely to develop the heart disease and diabetes risk factors.

Whole grains, nuts, and many fruits and vegetables are excellent dietary sources of magnesium.

"These foods have long been recognized as being healthy foods that may protect people from disease," researcher Ka He, MD, ScD, tells WebMD. "Magnesium could play an important role in this, but it is just one component of diet -- and diet is just one component of a healthy lifestyle."

The study group consisted of 4,637 young adults between the ages of 18 and 30 when enrolled in the mid-1980s. Fifteen years after entering the study, just over 600 had developed metabolic syndrome.

The researchers divided all the participants into four equal-sized groups based on their reported magnesium intake.

Daily Recommendations

The National Academy of Sciences recommends a daily magnesium intake of 400 milligrams and 310 milligrams, respectively, for adult males and nonpregnant females age 19 to 30. The recommended levels are 420 milligrams for adult males over 30 and 320 milligrams for adult nonpregnant females over 30.

He and colleagues concluded that people in the study who consumed the most magnesium had a 31% lower risk of developing metabolic syndrome, compared with people who ate the least.

Higher magnesium intake was associated with reduced risk of the individual risk factors that make up metabolic syndrome compared with those with the lowest intake.

The findings are reported in the April 4 issue of the American Heart Association journal Circulation.

Foods, Not Supplements

The researchers noted that the findings need to be confirmed in clinical studies. These studies are also necessary, He says, for determining the optimal daily dosage of the nutrient for people at risk for heart disease or diabetes.

He adds that foods, not dietary supplements, are the best sources of magnesium. Almonds, cashews, soybeans, spinach, avocados, whole grains, beans, and some fish are good food sources of the nutrient.

"Magnesium-rich foods are also rich in other nutrients, which may also be important for reducing risk," he says.

Cardiologist Nieca Goldberg, MD, worries that that message may be lost on many people who think they can take the easy way out with dietary supplements. Too much magnesium from supplement sources (outside of food) can cause problems ranging from weakness and nausea to toxic effects on the heart and nervous system.

"Certainly it is easier to go out and buy a bottle of pills than make the commitment to eating a healthier diet," she says. "But I can tell you from experience that when people make that commitment it really does pay off."

Goldberg is chief of the Women's Cardiac Care center at New York's Lenox Hill Hospital.

In addition to eating a diet rich in vegetables, fruits, whole grains and nuts, she recommends limiting simple carbohydrates, like those found in pasta and other white-flour based foods.

And both Goldberg and He agree that diet is just one factor in reducing heart disease and diabetes risk.

"People should eat healthy foods that are rich in magnesium to reduce their risk," He says. "But exercising regularly, not smoking, and maintaining a healthy body weight are also very important