With commentary by study lead author Nancy J. Brown, MD, professor of medicine and pharmacology at Vanderbilt University School of Medicine.
Viagra, a drug better known for its ability to improve men's erections, can also help improve insulin sensitivity in those who have prediabetes, potentially helping to delay or avoid the onset of type 2 diabetes, according to new research.
Researchers at Vanderbilt University School of Medicine looked at how sildenafil (Viagra) affected insulin sensitivity compared with placebo, says study leader Nancy J. Brown, MD, professor of medicine and pharmacology.
Her team randomly assigned 21 men and women to take sildenafil, 25 milligrams three times a day, and 21 others to take a placebo pill. Neither group knew which they were taking during the three-month regimen.
The average age in both groups was about 50. The average body mass index (BMI) was about 36, considered obese.
Those who took the sildenafil ''had a 20% improvement in insulin sensitivity compared to placebo," Dr. Brown says. The more insulin sensitivity a person has, the less insulin is needed to lower blood sugar levels. If a person has insulin resistance, their body can't make enough insulin to clear blood sugar, or it doesn't work well enough to lower the sugar.
The research is published online Nov. 18 in The Journal of Clinical Endocrinology & Metabolism.
In the U.S., 29 million people have type 2 diabetes, according to the Endocrine Society. About 3 in 10 people have prediabetes, in which the blood sugar levels are high but not high enough to be diagnosed as diabetes.
"We know a percentage [with prediabetes] go on to develop diabetes," Dr. Brown says. "The gold standard to preventing that is diet and exercise," Dr. Brown says. Yet, many patients find it difficult to keep up with a diet and exercise program, or to keep off the weight once they have lost it, and need more help, she says.
Drugs like sildenafil may help, she says. It works by inhibiting an enzyme that normally breaks down a chemical, cGMP, to relax the blood vessel. The chemical cGMP increases insulin sensitivity in muscle, according to the researchers.
Before doing the study, Dr. Brown says, the research team thought the drug would affect insulin secretion in response to glucose. "We found we were affecting insulin sensitivity," she says, and that was consistent with her previous research in animals. The researchers evaluated the effects of the drug and placebo by giving an infusion of glucose and then measuring the amount of insulin released.
They did not ask the men about any changes in erections, Dr. Brown said. That was to keep the study ''blinded,'' with neither group knowing if they were on the drug or the placebo.
The researchers also took urine samples and found that those on the drug had lower levels of the substance albumin in the urine, which reflects better kidney health, Dr. Brown says.
The study was small, but well done, says Joel Zonszein, MD, director of the Clinical Diabetes Center at Montefiore Medical Center and professor of clinical medicine at Albert Einstein College of Medicine, New York, who reviewed the findings.
However, the effect on insulin sensitivity was minimal, in his view. "I don't think it is going to be common [to use sildenafil] in the clinical arena," he says, unless a drug company steps in to develop a similar drug more specifically designed to affect peripheral tissues.
However, Dr. Brown says, some existing drugs to prevent diabetes may have negative effects on the heart, or not be good for patients with kidney disease, so more and alternative therapies are needed. She plans to continue to research the area.