To Your Good Health
DEAR DR. ROACH: I am grateful for your recent explanation of statins and beta blockers. Could you also explain what calcium channel blockers do and how they work? I once read they have nothing to do with the mineral calcium. Is that right? Do they interact with statins? — A. B.
ANSWER: Calcium channel blockers have everything to do with the mineral calcium. Calcium is used as a messenger in the body to turn on and off important cellular functions. Although there are many kinds of calcium receptors, the two kinds that are important for the calcium blockers we use clinically are those in the heart and those in the blood vessels.
In the heart, blocking calcium channels slows the heart rate and decreases the strength of the heart's contractions. The calcium channel blockers verapamil and diltiazem work predominantly this way. These drugs are useful for people with high blood pressure and some kinds of too-fast heart rhythms.
Blocking calcium channels in the blood vessels opens them up. Amlodipine, nifedipine and many other calcium blockers ending in "-pine" work this way and are useful for blood pressure control and in people with spasm of blood vessels.
An example is Raynaud's phenomenon, where blood vessels constrict excessively in response to cold.
What you may have heard is that dietary calcium has very little or no effect on the action of calcium channel blockers, which is true. People on calcium channel blockers have the same dietary calcium needs as anyone else.
Some calcium channel blockers, such as amlodipine (Norvasc and others), inhibit an enzyme (CYP3A4) that metabolizes some statin drugs, such as atorvastatin (Lipitor). This has the effect of raising the statin levels in the blood, so clinicians should be cautious in prescribing high doses of some statins in people taking calcium channel blockers.
DEAR DR. ROACH: I hear about insulin resistance all the time. What is it and how do you prevent it? — M. E.
ANSWER: Insulin lowers blood sugar levels by moving the sugar into the cells that need it. Without insulin, cells starve for energy despite very high amounts of sugar in the blood.
A small amount of insulin should drop the blood sugar dramatically.
In people with insulin resistance, the effect of insulin is blunted. In such people — like those with Type 2 diabetes or prediabetes — insulin blood levels are usually higher than they are in people without diabetes. This is often, but not always, in conjunction with obesity. However, there are several other causes of insulin resistance, including medications, stress, pregnancy, anti-insulin antibodies and genetic causes.
Glucocorticoids such as prednisone cause insulin resistance, and stress causes the body to release its own glucocorticoid (cortisol) as well as other hormones that oppose the action of insulin.
There are many other drugs that can cause insulin resistance, predisposing people to weight gain and even overt diabetes. Among these, beta-blockers, niacin, birth control pills and HIV medications are among the most important.
Insulin resistance may not be completely preventable, but it can be minimized. The most important way to do this is by having a normal body weight.
Exercise directly reduces insulin resistance, even if body weight stays the same. This is one reason exercise is frequently recommended: It can make big improvements in health, even if a person doesn’t lose a pound.