THE NUMBER NEEDED TO TREAT NNT
represents an estimate of the number of people who need to undergo the treatment of interest in order to prevent one additional adverse outcome from occurring. For example, if an intervention has an NNT of 10, it means you’d have to treat 10 people with that specific intervention to prevent one additional bad outcome.
As a measurement, the NNT is considered to be more clinically useful than sorting through relative risks, odds ratios or absolute risk reduction.(1) But it’s important to understand the population that was studied and what the specific outcome of interest is. For example, a medication used to prevent heart attacks from occurring will have one NNT for people who have never had a heart attack but probably a different NNT when it’s used for people who are trying to prevent a second incident.
The NNT is typically included in the results of research studies and reviews. An organization called The NNT Group reviews various therapies and diagnostic interventions and lists the findings on its website, thennt.com.
NNTs and Statins
Time frame matters too. According to The NNT Group, statin drugs given for five years, in order to prevent heart disease in people who have no history of heart disease, is 104.(2) That means that 104 people have to take statins in order to prevent one extra person from having a heart attack. The NNT Group calculates the number needed to harm (NNH) as well. According to its findings, one in 50 people on statins develops diabetes and one in ten experiences muscle damage as defined as rhabdomyolysis. Undiagnosed muscle pain, such as myalgia, wasn’t included.
The picture changes when considering patients who have a history of heart disease. In this case, according to the reviewers, the statins NNT is 83 in order to prevent an additional death from occurring and 39 for preventing a nonfatal heart attack.(3) The harms are the same as in the previous instance.
In comparison, the Mediterranean diet has been studied in a large randomized trial and is included on The NNT website. When followed for five years, the Mediterranean diet has an NNT of 61 for preventing stroke, heart attack or death with no harms noted.(4) So, according to The NNT, the Mediterranean diet appears to be a better choice than statins for primary prevention of stroke, heart attack or death.
When the focus is shifted to studies on patients who’ve had one heart attack and are trying to prevent a second one, the NNT for the Mediterranean diet drops even lower. In fact, the NNT for preventing that repeat heart attack is 18, and the overall NNT for preventing death or cancer in this group is 30.(5)
1. Centre for Evidence-Based Medicine. Number Needed to Treat (NNT). www.cebm.net/number-needed-to-treat-nnt
2. The NNT. Statins for Heart Disease Prevention (Without Prior Heart Disease). www.thennt.com/nnt/statins-for-heart-disease-prevention-without-prior-heart-disease
3. The NNT. Statins for Heart Disease Prevention (With Known Heart Disease). www.thennt.com/nnt/statins-for-heart-disease-prevention-with-known-heart-disease
4. The NNT. Mediterranean Diet for Heart Disease Prevention (Without Known Heart Disease).www.thennt.com/nnt/mediterranean-diet-for-heart-disease-prevention-without-known-heart-disease
5. The NNT. Mediterranean Diet for Post Heart-Attack Care. www.thennt.com/nnt/mediterranean-diet-for-post-heart-attack-care