Women who feel bloated, irritable or depressed before getting their periods — classic signs of premenstrual syndrome, or PMS — may want to pay attention to the amount of iron in their diets, according to a new study.
Researchers at the University of Massachusetts at Amherst found that women with an iron intake of more than 20 milligrams a day had about a 35 percent lower risk of being diagnosed with PMS than women who had the lowest iron intake, about 10 mg a day. To get the higher amount, a woman would only have to eat one cup of iron-fortified cereal, which typically contains about 24 mg of the mineral.
PMS affects anywhere from 8 to 15 percent of women during their childbearing years and is characterized by physical and emotional symptoms ranging from breast tenderness and food cravings to fatigue and moodiness.
Other research has shown that diet affects the development of PMS or may ease the severity of its symptoms. For example, diets high in calcium-rich foods have been shown to lower the risk of PMS, but little was known about the role other minerals might play in preventing the symptoms.
For the study, researchers reviewed three sets of food frequency questionnaires collected over a 10-year period from more than 3,000 American women, ages 25 to 42. All the women were enrolled in the ongoing Nurses' Health Study II, which is exploring the influence of diet and lifestyle on women's health.
Researchers compared the mineral intakes from food as well as supplements for nearly 1,060 women who had been diagnosed with PMS against those of roughly 1,970 women who had few if any PMS symptoms.
The scientists also considered other factors linked to PMS, such as a woman's age, weight, pregnancy history, use of oral contraceptives and her smoking and exercise habits.
"We were somewhat surprised by our findings for iron since no previous studies had observed this relationship," said study author Elizabeth Bertone-Johnson, Sc.D., an associate professor of epidemiology at UMass Amherst.
But not all forms of dietary iron are the same. It was primarily the iron found in plant foods and in supplements, non-heme iron, that reduced a woman's chances of developing PMS. The heme iron coming from animal sources, such as red meat and poultry, did not have the same effect.
Bertone-Johnson suspects that non-heme iron had a stronger relationship with PMS because it's easier to eat a diet rich in plant and supplement sources. For example, three-quarters of a cup of fortified cereal has 18 mg of non-heme iron, and a cup of lentil or beans has between 3 and 7 mg. But a 3-ounce serving of beef has only 2 to 3 mg of heme iron, so you would need to eat a large serving of beef to meet your daily iron needs, which is not advisable considering its saturated fat content.
The study, which was published online on Feb. 26 in the American Journal of Epidemiology, evaluated data for eight different minerals.
Potassium: A surprising finding
Iron was not the only mineral linked to an improvement in PMS symptoms. The study found some evidence that a zinc intake of more than 15 milligrams a day was associated with a lower risk of PMS. But this effect was only seen for zinc supplements and not for food sources of the mineral.
Although the role zinc may play in PMS needs to be evaluated in greater detail, deficiencies of the mineral may be linked to mood-related symptoms like depression and possibly menstrual cramps, Bertone-Johnson said.
Researchers found no connection between intakes of sodium, magnesium or manganese and PMS. But it was a completely different story for potassium; high intakes of this mineral were linked to a greater risk for PMS.
"We saw a 46 percent increase in the risk of PMS only among women with the highest level of intake, which was approximately 3,700 milligrams a day. This was compared to women consuming the lowest amount, or roughly 2,300 milligrams," Bertone-Johnson said.
Potassium, found in foods such as sweet potatoes, bananas and orange juice, may increase a woman's chances of developing PMS by boosting levels of a hormone linked to water retention. The mineral may also contribute to other physical and emotional symptoms, such as bloating, depression and irritability.
"We were surprised to find that potassium intake was associated with a higher risk of PMS, as this was contrary to our expectations," Bertone-Johnson said.
Because the effects of potassium on PMS need further investigation and the mineral is an important component of a healthy diet, Bertone-Johnson said she would still encourage women who have PMS to consume the recommended daily allowance (RDA) for potassium, or 4,700 mg a day. But they should not go considerably higher than that amount.
"Our findings suggest that minerals, including iron and zinc, may be involved in PMS, but this needs to be replicated in other studies," Bertone-Johnson said.
For now, she suggests that women experiencing PMS symptoms meet the RDA for these minerals: 18 mg a day for iron and 8 mg a day for zinc. She also recommends getting 1,000 mg of calcium daily, the RDA for this mineral.
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