A link has been found between daily energy drink use and chronic insomnia among college students. Research suggests that 51% of women and 37% of men who consume energy drinks have difficulties sleeping. Among men and women who rarely or never consume energy drinks, there is a 20% drop in sleep difficulties. Women who drink energy drinks daily have an 87% higher likelihood of sleeping fewer than six hours per night. These types of beverages generally contain about 75–150 mg of caffeine per can, and many students consume several a day. This would come close to, if not exceed, the daily recommended limit of caffeine for one person, which is 400mg. Although researchers say there is not yet a direct correlation, poor sleep could be causing students to consume caffeine, not the inverse.