Is your iPad an anti-sleeping tablet?

Many people spend their last moments before sleep reading on a tablet computer or checking messages on a smart phone. Researchers at the Mayo Clinic wondered whether the light emitted by such devices might be disrupting users' sleep patterns.

The initial findings of a sleep study suggest that dimming a smartphone and holding it at least 14 inches from your face might help you sleep better.

Dr. Lois Krahn, a psychiatrist at Mayo's Scottsdale, Ariz., clinic, conducted the study to determine if smartphones and tablets were interfering with melatonin, a hormone that helps control the body's sleep cycle.

"The question is does a tablet or mobile device emit enough light to be a problem?" Krahn said on the Daily Circuit.

Krahn's research involved measuring the light two different tablets and a smartphone emitted in a dark room. The measurements were made at various distances.

Research looked at a variety of devices, positioned 14 inches from the eye.

"We found that they do not emit enough light to be a problem" at that distance. "If you have it right up to your nose, that's different" but "dimming the light just a little bit really puts you in a safe place."

Melatonin is secreted when we people are in the dark, so that's why it's harder to sleep in a bright room even if our eyes are closed. "Our bodies are still aware of the light."

As devices evolve, there are concerns they not become brighter. "We're in a world filled with mobile devices. We have to understand how they affect our sleep and our functioning, " Krahn said.

Below are Krahn's recommendations, based on the study:

• Use middle or low settings for brightness on your smartphone or tablet. Only the highest brightness setting might affect melatonin.

• Keep the device at least 14 inches from your face