Studies have linked poor sleep to obesity and other health problems, and now new research suggests a reason why.

The study, of 38 men with and without chronic insomnia, found that those with the sleep disorder had 30 percent lower nighttime levels of the hormone ghrelin, which is involved in appetite control.

A number of studies in recent years have highlighted the role of sleep in overall health. Research has linked poor sleep — owing to sleep disorders or shift work, for example — to higher risks of obesity, diabetes and heart disease.

These latest findings, reported in the journal Psychoneuroendocrinology, help shed light on why sleep deprivation might encourage weight gain and its related health consequences.

"We are just starting to understand how hormones that we thought were specifically related to energy metabolism and appetite can be affected by poor sleep," lead researcher Dr. Sarosh J. Motivala, of the University of California Los Angeles, told Reuters Health.

"This study suggests that altered hormone regulation could explain why some insomnia patients gain weight over time."

For the study, Motivala and his colleagues had 14 men with chronic insomnia and 24 healthy men spend two nights in the sleep lab. The researchers used a catheter to periodically take blood samples from the men as they slept, looking for fluctuations in the hormones leptin and ghrelin.

Leptin, which helps regulate body weight, is secreted by fat cells; low blood levels of leptin promote hunger, while increases tell the brain the body is full and encourage calorie burning. Ghrelin is secreted by the stomach to boost appetite.

In this study, men with chronic insomnia had lower overnight levels of ghrelin compared with their healthy counterparts. While that might seem like a good thing, the findings actually point to a problem in ghrelin regulation in men with insomnia, according to Motivala.

It's possible, he explained, that insomnia patients' ghrelin levels are lower than normal at night, but elevated during the day — possibly boosting appetite.

On the other hand, he added, people with chronic insomnia may have consistently lower levels of the hormone, pointing to general dysregulation in how ghrelin is "expressed" in the body.

Motivala said he and his colleagues are trying to answer this question in an ongoing study of men and women with insomnia.