Women are more likely to crave chocolate during their menstrual periods than at other times of their cycles, a study of Kansas State University undergraduates has found.

Chocolate, offered in five forms, was the only food of 32 kinds studied in which strength of the participants' craving varied significantly when they were menstruating.

The study encompassed 83 single, white female students in a nutrition class. Once a week they were offered a pair of foods drawn from two of five categories: chocolate-flavored items such as cake, candy bars and ice cream; comparable nonchocolate foods; other high-sugar foods; low-carbohydrate foods such as hamburgers, tacos and pizza; and high-starch foods such as bread, popcorn and potato chips.

The women were asked which item in a pair they preferred and how strong their preference was. The women were also asked about their menstrual cycles, along with other health information. Only the preference for chocolate fluctuated with the menstrual cycle.

Chocolate is known to have various, usually mild, physiological effects such as narrowing the blood vessels, raising blood pressure and altering intestinal peristalsis. Chocolate also contains caffeine and theobromine, both stimulants. Theobromine is also reputed to produce subtle feelings of comfort and pleasure.

The researchers, Katharine Grunewald and Regina Tomelleri, say that while women may be seeking some of these effects to offset menstrual cramps or other unpleasant aspects of the menstrual period, they have no explanation for the preference.