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A drop in blood potassium levels caused by diuretic thiazides could be the reason why hypertensive patients taking these drugs are at higher risk for developing type 2 diabetes, according to a new study.
The drugs helpfully accelerate loss of fluids, but also deplete important chemicals, including potassium.
“Previous studies have told us that when patients take diuretic thiazides, potassium levels drop and the risk of diabetes climbs to 50%,” says lead researcher Tariq Shafi, MD, Department of Nephrology, Johns Hopkins University School of Medicine, Baltimore, Maryland. “Now, for the first time, we think we have concrete information connecting the dots.”
For the study, researchers examined data from 3,790 nondiabetic participants in the Systolic Hypertension in Elderly Program (SHEP) — a randomized clinical trial conducted between 1985 and 1991 designed to determine the risk versus benefit of giving a certain hypertension medication to people aged 60 years or older.
Half of the subjects were treated with chlorthalidone and half with a placebo. Of the 3,790 subjects, 1,603 were men and 724 were nonwhite. None had a history of diabetes. In the original study, potassium levels were monitored as a safety precaution to guard against irregular heartbeat.
Results of the study showed that for each 0.5 MEq/L decrease in serum potassium, there was a 45% increased risk of diabetes. None of the people in the group receiving placebo developed low potassium levels.
Dr. Shafi said these findings should encourage physicians to establish a potassium baseline by checking hypertensive patients’ medical records to determine their potassium levels before prescribing thiazides.
“We would normally look at the number only after 6 weeks of treatment to make sure it was not low enough to cause heart problems. As a result, we might not be aware that it dropped significantly from where it was before treatment, putting the patient at risk for developing diabetes,” he said.
Hypertension, Nov, 2008