Expert: William B. Jeffries, Ph.D. - 2/18/2006

Question
I have been taking HCT for decades. I have occasionaly had sun induced rash (tennis) and have recently read that usage may increase probability of onset of diabetes. I am 70 yrs old, exercise often(run), weigh 160 lbs(height 5' 10"), and have no health problems except hypertension(poorly controlled) and mildly elevated cholesterol (controlled). I also take Micardis(80mg)
Should I be concerned about HCT?

Answer
At higher doses, hydrochlorothiazide can increase blood sugar levels, which is the primary problem in diabetes.  Research has shown thiazides reduce blood potassium levels, which causes blood sugar to rise.  If potassium loss caused by thiazide diuretics is prevented, then blood sugar levels will not rise.  

In recent long-term clinical trials, treatment with a thiazide diuretic was associated with a slight increase in blood glucose levels; however it is unknown whether long-term control of blood potassium will prevent this small increase in the incidence of diabetes.  

In the same studies, thiazide diuretics have been found to significantly reduce the incidence of illness and death due to cardiovascular disease such as heart attack, heart failure and stroke.  Thus the potential benefits of these drugs are currently considered to far outweigh the risks.  This is why the current national recommendations for the treatment of hypertension say that most patients with hypertension should be placed on a thiazide diuretic (see this link: http://www.nhlbi.nih.gov/guidelines/hypertension/express.pdf)

If you are concerned about your blood sugar, then it is important to ensure that blood potassium is also high enough while taking a thiazide.  Ask your doctor about your potassium and what you can do to ensure it stays in the normal range.  He/she will likely encourage you to maintain adequate potassium intake (raw fruits and vegetables), or prescribe potassium supplements or an additional drug to control the loss of potassium.