Women who say they feel stressed early in their menstrual cycle are more likely to report the cramping, bloating and mood swings of PMS — premenstrual syndrome — later in the month, a new study shows.

Researchers from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, along with researchers from other institutions, quizzed 259 women of childbearing age about their stress levels. The women were asked how often they felt unable to control their lives, and how often they felt nervous, for example. Study participants who reported a lot of stress early in the menstrual cycle were subsequently more likely than relaxed women to report moderate or severe discomfort before and during menstruation. Furthermore, all of the women in the study were followed for more than one cycle; among women who reported stress in one month and not in the next month, the more stressful month was, on average, followed by worse symptoms of PMS. The results up held after statistical adjustment for the women’s age, education, smoking status and weight-to-height ratio.

It is not totally clear why stress might affect a woman’s physical comfort and mood even weeks later, before and during her period. But stress is a hormonal process, and so, of course, is much of the work of the reproductive system. Writing in the Journal of Women’s Health, the researchers say that stress may have an impact on PMS through several channels: perhaps by altering levels of ovarian hormones, or perhaps because the stress hormone cortisol has an impact on PMS symptoms. “Stress-reduction programs,” the researchers write, “may be an effective, nonpharmaceutical treatment” for both physical and psychological symptoms of PMS.