DEAR DR. ROACH: A cardiologist recently suggested that I should consider taking a statin because of my “borderline” cholesterol level. So, I took a dive into the details of statin therapy. I learned that although statins are thought to reduce the chance of a cardiovascular event by up to 50%, the actual reduction is very small.

I presented this information to the cardiologist and decided to forego statin therapy, which he endorsed. A better understanding of this difference would be very valuable to your readers. — T.G.

ANSWER: The amount of absolute risk reduction from a statin in a person without known heart disease depends mostly on a person’s absolute risk of heart disease. This depends on the person’s risk factors such as age, sex, blood pressure, cholesterol level, smoking status, family history, and other risk factors. (When a person already has known heart disease, then the benefits of a statin are so large that this kind of analysis isn’t generally done.)

The relative risk reduction from a statin depends on the potency and dose of a statin, but a typically used number is about a relative risk reduction of 20%. (A 50% relative risk reduction isn’t achievable with the current medication.)

I normally go through this analysis with every patient when considering a statin, and it starts with estimating their absolute risk prior to treatment. There are several calculators to give an estimate; I usually use tinyurl.com/PREVENTCalc and adjust it for any risk factors that are not considered by the calculator. (I should add that some people just have difficulty understanding these numbers and simply ask me about my opinion, which is fine, but I prefer to work collegially.)

For example, a 75-year-old man who has a cholesterol of 220 mg/dL and an HDL of 45 mg/dL with a blood pressure of 140/80 mmHg (all of which might be considered “borderline”), the calculator gives an estimated absolute risk of 19.4%. This is the risk of this person developing any kind of obstructive heart disease, including a heart attack or death, during the next 10 years.

With a statin, a reasonable guess would be a drop of about 20% of the absolute risk (19.4% in this case), meaning a drop to 15.5%. The relative risk reduction is 20%, but the absolute risk reduction for this person is 3.9%.

A second example is a 50-year-old woman with the exact same numbers who has an absolute risk of 3.6%. She would get the same 20% reduction, but this is only a 0.72% drop for a new absolute risk of 2.88%.

Clinicians and epidemiologists use another number called the “number needed to treat” (NNT), which is a function of the absolute risk reduction. In the examples above, about 26 75-year-old men would need to be treated for 10 years to prevent a case of heart attack or death, while 139 50-year-old women would need to be treated to prevent one case.

The benefit of a statin or any other treatment to reduce heart disease depends on how much risk a person has to begin with. Whether this benefit is “worth it” to any given person depends not only on the absolute benefit, but also on their aversion to medicine and their level of worry about heart disease.

The cost of a statin ($5 or $10 a month) isn’t a big consideration for most. Serious side effects to statins are rare, but if they occur, there are alternatives.

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Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu.