An evening snack of dark chocolate may be the key to getting a good night's sleep. British researchers found that magnesium, an essential nutrient found in dark chocolate, helps cells keep track of the natural cycles of day and night.

Researchers at the University of Edinburgh and the MRC Laboratory for Molecular Biology in Cambridge discovered that concentrations of magnesium rose and fell in a 24-hour cycle in all types of cells.

This ebb and flow influences the cells' internal clocks — the sleeping and waking cycles called circadian rhythm, as well as the release of hormones, body temperature, and other bodily functions.

"Internal clocks are fundamental to all living things," said Dr. Gerben van Ooijen, of Edinburgh University. "They influence many aspects of health and disease in our own bodies, but equally in crop plants and micro-organisms."

The study showed that magnesium also has an impact on metabolism, helping regulate when and how quickly organisms convert food into energy.

The new findings could help the development of chronotherapy, which would determine the best time for medical treatments, and to increase yields and determine harvesting seasons in agriculture.

Previous research shows that magnesium provides a wide range of health benefits, including boosting the immune system and lowering the risk of heart attacks. Studies have also shown that people who have migraines tend to have lower levels of magnesium than those who are headache free.

Although magnesium is readily available in supplements, nutritional experts say it's best to get magnesium from your diet.

In addition to dark chocolate, magnesium is also found in many foods including green leafy vegetables, whole grains, avocados, nuts, seeds, yogurt, and bananas.

The study was published in Nature.