Jeff is a 19 year old college student who usually climbs into bed around 1:00 AM and gets up about six hours later. That's not to say Jeff is sleeping those 6 short hours; his TV is on for awhile, but then Jeff and his friends sometimes text each other throughout the night.

Jeff's case is becoming more typical.  National and international studies are drawing the same conclusions:

"Mobile phone use after lights out is very prevalent among adolescents," according to a study by the JFK Medical Center in Edison, N.J. "Its use is related to increased levels of tiredness. There is no safe dose and no safe time for using the mobile phone for text messaging or for calling after lights out."

The study finds that older students tended to be awakened by a text message more often during the night than their younger counterparts. Researchers also found that older teens who are awakened by text messages reported being more tired than those who are never awakened during the night.

"Concerns about media use should not be limited to television," the authors conclude. "Mobile phone use for text messaging and Internet use are related to sleep behavior as well."

For the JFK Medical Center study, 40 kids, ages 8 to 22, filled out questionnaires regarding their phone habits. The hospital also conducted research, in part, with teenaged patients, with hospital staff getting a firsthand look at teen's almost compulsive need to stay connected.

The medical center said it has a video tape of a nurse asking a teenage patient if his cell phone is off.  The patient answers, "Yes", but is then seen texting as he is monitored on videotape during a night's stay at the center.

A 2010 Neilsen Company study showed teens aggressively use their cell phones to text, surf the web, listen to music, play games, and sometimes talk.

But more and more, kids are staying up late, sometimes four hours past their bedtimes, to feed their addictions. And if they receive texts after they've fallen asleep, they'll usually wake up to answer them.

While this may seem like nothing more than an annoying form of teen rebellion, doctors worry the lack of sleep could lead to serious mood and cognitive problems, like anxiety, depression, ADHD and learning difficulties.

Lack of sleep at night might not be the only reason to worry about teens and their texting addictions. They could develop physical injuries in their hands, wrists, and fingers.

Doctors report more patients complaining of tingling, numbness and pain in their fingers and wrists. Since this is a relatively recent complaint, at least in large numbers, physicians are looking around for a recent phenomenon that might explain it. Their attention quickly fell on texting.

With over 152.7 billion text messages sent per month in the United States alone, it is becoming clear that people are shifting their primary method of communication from voices to hands and fingers. Does this shift explain the injuries?

While these complaints can all be signs of tired, overused hands, these symptoms can also indicate something more serious, such as a repetitive stress injury, tendonitis, aggravation of arthritis or sprains, and even carpal tunnel syndrome, doctors say.

"It is important that patients don't dismiss symptoms of sore fingers, occasional numbness and tingling", says George Kardashian, M.D., an orthopedic surgeon and hand specialist at The Center for Bone and Joint Disease in Hudson, FL. "These symptoms are all the body's way of saying it needs a break or a more serious injury will occur."

Kardashian suggests patients take frequent breaks from texting and typing and stretch the affected areas if experiencing any symptoms. If pain and/or swelling exist, use ice packs to reduce swelling while giving your hands a rest.

Or maybe turn off the cell phone and get a full night's sleep.