Women who eat a diet rich in B vitamins have less risk of premenstrual syndrome (PMS), a new study says.

Those who ate more of foods such as spinach and fortified cereal had about a quarter lower risk of PMS, according to the study in the American Journal of Clinical Nutrition. The same was not true, however, for women who got their B vitamins from supplements.

Thiamine and riboflavin are two of the many kinds of B vitamins. The study does not mean that thiamine and riboflavin themselves stave off PMS; it’s possible, for example, that women who eat more of the vitamins also have other habits or characteristics that have an effect.

Still, women who might be concerned with getting PMS “might want to evaluate their diet and make sure they’re having a reasonable (amount) a day of thiamine- and riboflavin-rich foods,” said Elizabeth Bertone-Johnson, associate professor of public health at the University of Massachusetts, Amherst.

Severe PMS - which affects about one in six women - is sometimes treated with either birth control pills or antidepressants, Bertone-Johnson, who co-authored the study, told Reuters Health.

Reducing the chance of PMS through diet may be an alternative to some of these treatments, which are expensive and can have side effects, she said.

The researchers looked at the diets of more than 3000 women, who filled out food surveys three times over 10 years. During this time, about 1050 women developed symptoms of moderate to severe PMS such as anxiety, depression, irritability, abdominal pain, fatigue and bloating.

The Institute of Medicine recommends adult women eat 1.1 milligrams each of thiamine and riboflavin per day. But the researchers found that higher amounts were needed to show a benefit, Bertone-Johnson said.

Women who reported eating about 1.9 milligrams of thiamine per day were less likely to come down with PMS - about two in five developed PMS compared to three in five women who ate about 1.2 milligrams a day.

The rates were the same for women who ate about 2.5 milligrams of riboflavin per day compared to women who ate around 1.4 milligrams per day.

It’s relatively easy to eat this much thiamine and riboflavin a day, Bertone-Johnson said. That’s about two to three bowls of fortified cereal, three quarters of a cup of dried beans, or about three ounces of red meat, for thiamine.

About one to two bowls of cereal provides this much riboflavin, or a three-ounce portion of cow’s liver.

This is the first time that food nutrients have been linked to PMS, said Ellen Freeman, professor of obstetrics/gynecology and psychiatry at the University of Pennsylvania in Philadelphia.

“It suggests that the B vitamins may have a role in the symptoms” of PMS, Freeman, who was not involved in the study, told Reuters Health.

Despite the fact that PMS has been studied for several decades, no one really knows what causes it, Bertone-Johnson said.