Women who get a little more than the recommended daily amount of iron in their diets may be less likely to get a more severe form of premenstrual syndrome (PMS), according to a new study.
Researchers followed about 3,000 women over 10 years and found that those who consumed more than 20 milligrams (mg) per day of iron sources were 30 percent to 40 percent less likely to develop PMS than women who got less of the mineral.
"Most previous studies of PMS have focused on effective treatments and factors that differ between women who have PMS and those who don't," said Elizabeth Bertone-Johnson, the study's lead author from the University of Massachusetts in Amherst.
"We were interested in looking further at some specific minerals," she added, noting that her team had previously studied the relationship between vitamin intake and PMS.
For the new study, the researchers limited their analysis to PMS in which symptoms such as breast tenderness, bloating, depression and anxiety are so severe they "substantially impair life activities and social relationships."
That type of PMS affects between 8 percent and 15 percent of U.S. women, they write in the American Journal of Epidemiology.
The study is based on data from a large ongoing study of U.S. nurses, who were between the ages of 25 and 42 years old in 1989, and it focuses on 3,025 women who did not have PMS in 1991.
Each woman completed three food questionnaires sent to them over the next 10 years, which asked how often they were eating 131 different types of foods and supplements.
The researchers then compared the diets of the 1,057 women who went on to develop severe PMS during the study period to the diets of the 1,968 women who did not.
Overall, eating a diet that provided about 22 mg of iron every day was linked to a 33 percent decrease in a woman's risk of developing PMS during those 10 years, compared to the women who ate the least amount of iron - about 10 mg.
Those 22 mg are a little more than the 18 mg of iron per day that's recommended for adult women, according to the researchers.
Even greater iron consumption was tied to an even larger drop in risk for PMS, but some of the women were eating diets with too much of the mineral.
"I think our message - based on these data - is meeting the (recommended daily amount) for iron seems to have a significantly lower risk for PMS. We don't want to recommend women take the upper limit (of 45 mg), because of potential adverse consequences," Bertone-Johnson said.
Women in the study with the highest iron intakes tended to get most of the mineral from non-meat sources.
The U.S. Institute of Medicine, which sets recommended dietary allowances for nutrients, points out that iron consumed from meat and poultry sources is more easily processed in the body, and that people who get their iron only from a vegetarian diet might want to consume as much as twice the recommended amount.
Although Bertone-Johnson said they can't prove iron prevents PMS, the researchers suspect the mineral may have something to do with the production of serotonin, a molecule that plays a role in many processes in the body and in the brain.
Iron is necessary for the body to manufacture serotonin, they write.
Among the new study's limitations is their reliance on the women's own reports of what they ate. The researchers write that additional studies are needed to confirm the new findings and to show that the benefits of getting more iron outweigh the risks.
Further research is also necessary, they say, to look at some of their other findings, including that women with the highest intakes of potassium were about 50 percent more likely than others to develop PMS.
"Our advice from this study is pretty similar to what we've taken from previous work… Not focusing on any one nutrient per say, just make sure your diet is balanced and you're meeting the (recommended daily amount) on your vitamins," Bertone-Johnson said.
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