It seems quite extraordinary that we prescribe statins to women when there is no evidence that doing so will significantly increase their life expectancy.
It is true that the statin trials have focused on men, so the data for women are less extensive.
But there is still a great deal of information from trials. A recent meta-analysis in The Lancet reviewed the evidence on primary prevention in women. It included data on 10,990 women treated for five years. In this analysis, not only was there no effect on overall mortality, there was no effect on CHD.
The data on secondary prevention are more fragmented and it is difficult to draw any firm conclusions.
However, existing data certainly do not suggest any significant benefit. The 4S study, for example, was by far the most positive of any of the statin trials done so far in men.
At the end of the 4S study four more women were alive in the placebo arm than in the statin arm. However, this arm of the study was underpowered to reach statistical significance.
The HPS study, which included more than 5,000 women, was hailed as being almost universally positive, and 'proving' that statins were as effective for women as men.
While it is true that in this high risk, secondary prevention study, women were significantly protected against stroke and CHD, the figures for overall mortality were absent.
The overall mortality data was eventually published, four years later, in an online medical journal.
The benefit on overall survival in women did not actually reach statistical significance. It is true that there were more women alive in the statin arm than the placebo arm.
If we use the concept of NNT, the HPS data suggest that we need to treat 2,542 women for five years to delay 36 deaths.
In order to provide the information in a way that is most meaningful to our patients, we need to be able to answer this question: what does a reduction of 36 deaths, over five years of a clinical trial, in 2,542 women, equate to in increased life expectancy?
To rephrase this question, if you are a high risk woman, how much longer can you expect to live?
It is not possible to answer that question with absolute certainty. Primarily because it is not known what the survival curves look like from beyond the trial period of five years. However, a basic model can be used (see diagram).
It is possible to establish that, after five years of treatment it would take about one year for the number of deaths in the statin arm to 'catch up' with deaths in the placebo arm.
Added life years
What has been achieved, therefore, by treating 2,542 people for five years, is to create 36 added years of quality life.
This means that 12,710 years of treatment results in 36 added life years, which equates to 353 years of treatment to increase life expectancy by one year.
Turning this equation the other way round it is now possible to calculate that one year of statin treatment will increase life expectancy by 1/353 years, or about one day.
This means that in a woman at very high risk of cardiovascular disease, 30 years of treatment with a statin will increase life expectancy by slightly more than a month on average.
This is the only statin trial done to have shown any impact on overall mortality in women and this was a very high risk group.
In lower risk and primary prevention there is no impact on overall mortality at all.
Despite this, if NICE decides to support the latest Joint British Societies' guidelines, around seven million women in the UK will be taking statins for the rest of their lives.
Dr Kendrick is a salaried GP in Manchester
- Statin trials have focused mainly on men.
- For primary prevention there is no impact with statins on overall mortality.
- The data on secondary prevention with statins in women is fragmented.
- One year of statin treatment will increase life expectancy by about one day.
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- Heart Protection Study Collaborative Group. The effects of cholesterol lowering with simvastatin on cause-specific mortality and on cancer incidence in 20,536 high-risk people: a randomised placebo-controlled trial. BMC Medicine 2005, 3: 6 www.biomedcentral.com/1741-7015/3/6 .