WASHINGTON (Reuters) - Doctors are reluctant to increase doses of patients' medications, even when their blood sugar, blood pressure and other symptoms are clearly out of bounds, experts told a diabetes meeting on Saturday.

Several studies showed that doctors are failing to prescribe higher doses of medicine or add new drugs for their patients with Type 2 diabetes when their blood glucose levels or high blood pressure go above the limits.

"Physicians have not typically been trained to continue to intensify things," said Dr. Alexander Turchin, an endocrinologist at Brigham and Women's Hospital and Harvard Medical School in Boston. "Physicians may be under appreciating the risk that hypertension places on diabetes patients."

Nearly 21 million people in the United States have diabetes, which contributes to more than 220,000 deaths a year and costs more than $132 billion annually, according to the American Diabetes Association.

Most have Type 2 diabetes, caused by a combination of genetic factors and lifestyle and closely linked with obesity and lack of exercise.

Diabetes patients have a much higher risk of heart and kidney disease, blindness and limb loss and must not only control their blood sugar, but must take care to keep their blood pressure and cholesterol low. Diet and exercise can do this but many patients also need drugs.

Studies presented to a meeting of the American Diabetes Association showed doctors in the United States, Germany and Britain are not stepping up the medications when needed.

Turchin's team reviewed records of 1,244 people with diabetes and high blood pressure who were treated by 166 physicians from 2000 to 2004.

Medications were intensified in only 26 percent of visits in which patients had too-high blood pressure. "Some of the reasons that are commonly given (are) that 'blood pressure is good enough,"' Turchin said.

Dr. Shari Bolen and colleagues at Johns Hopkins University in Baltimore studied the records of 254 government employees and family members with Type 2 diabetes and high blood pressure who were in a managed care program.

Doctors prescribed better doses of drugs only 12 percent of the time when blood pressure was clearly above limits.     Bolen said patients in her study had insurance and tended to take medicine as prescribed, but doctors failed to prescribe higher doses or different medications when warranted.

Dr. Stephen Gough of Britain's University of Birmingham and colleagues studied data from records from 1,600 doctors in Britain and Germany and found the patients' blood sugar was poorly controlled.

They looked at a measurement called A1C, which shows what a person's average blood sugar level has been for the past three months. On average it was 8.4 percent, Gough said -- above the recommended 7 percent.