A 10-year study of more than 3,000 women has found that dietary iron may reduce the risk for premenstrual syndrome, while potassium intake may increase it.

Using data from a larger analysis of women’s health, researchers studied 1,057 women with PMS and 1,968 control subjects. They used questionnaires to establish their nutrient intake, both food and supplements, and established cases of PMS by clinical diagnosis.

After controlling for various health and dietary factors, they found that women in the highest 20 percent for iron intake were about 40 percent less likely to suffer PMS as those in the lowest 20 percent.

The study, published online in The American Journal of Epidemiology, found the opposite effect with potassium. Those in the highest 20 percent of intake had a 46 percent increased risk for PMS compared with those in the lowest 20 percent. There was no risk associated with intake of magnesium, zinc, manganese, copper or sodium.

The senior author, Elizabeth R. Bertone-Johnson, an associate professor of epidemiology at the University of Massachusetts, cautioned women against taking too much iron, or consuming too little potassium, both of which can be harmful. “Eating a balanced diet with a variety of foods,” she said, “is a good way to ensure that women are consuming important vitamins and minerals.”

The Food and Nutrition Board of the Institute of Medicine recommends 18 milligrams of iron daily for women 19 to 50, and 4,700 milligrams of potassium a day for all adults.