Gastric bypass and other weight-loss surgery sometimes lead to a dangerous vitamin deficiency that can cause memory loss, confusion, lack of coordination and other problems, according to a new study.

The deficiency, called Wernicke encephalopathy, affects the brain and nervous system when the body has too little vitamin B1 (thiamine). It can also cause vision problems.

It happens most often in people who have frequent vomiting after the surgery, which is not uncommon.

The study, published in the March 13, 2007 issue of Neurology, the scientific journal of the American Academy of Neurology, looked at 32 cases of Wernicke encephalopathy. Many of these people also had unusual neurological symptoms, such as seizures, deafness, psychosis, muscle weakness and pain or numbness in the feet or hands.

"When people who have had weight loss surgery start experiencing any of these symptoms, they need to see a doctor right away," says study author Sonal Singh, M.D., of Wake Forest School of Medicine in Winston-Salem, North Carolina. "Doctors should consider vitamin B1 deficiency and Wernicke encephalopathy when they see patients with these types of neurological complications after weight loss surgery. If treated promptly, the outlook is usually good."

The treatment is simple vitamin B1 replacement through an IV or injection. Of the 32 people studied, 13 made a full recovery. Unfortunately, many continued to have memory problems, weakness or difficulty coordinating physical movements.

Singh says more research is needed to determine how common the condition really is. He points out that some doctors prescribe B1 to all their patients who have had weight-loss surgery but recommends that national standards be set for all doctors to follow.