Zissimopoulos and colleagues have published a freely accessible paper in JAMA Neurology titled ‘Sex and Race Differences in the Association Between Statin Use and the Incidence of Alzheimer Disease’.
The researchers conclude that statins are linked to a reduced incidence of Alzheimer’s Type Dementia. They further hypothesise that specific statins are linked to reduced incidence of Alzheimer’s Type Dementia according to ethnic and gender groupings.
I won’t go into detail here as the reader can access the paper via the link above.
We can however ask the question – how convincing is the evidence for the relationship? I will start by saying that I am convinced by the paper of a relationship between statins and incidence of Alzheimer’s Type Dementia. There is biological plausibility for this relationship and it also fits with other research findings. The researchers have used a large sample set and from my reading of the paper this looks to be an epidemiological study. The researchers have pulled medicare data which benefits from a large coverage of the U.S population.
The drawback of epidemiological data is that we can’t be certain of the quality of the data. In this study, more specifically we can’t be certain of the following assumptions
- If a person prescribed a statin is taking that statin
- If a person without a diagnostic coding for Alzheimer’s Type Dementia does not have Alzheimer’s Type Dementia
The model rests on a number of implicit assumptions. The conclusions are not just that statins are associated with a reduced incidence but more specific conclusions linked to individual statins.
In this regards the authors are bold to detail very specific hypotheses about individual statins. My impression is that there may be a lot of ‘noise’ in the data generated by assumptions in the model such as those described above and that this may account for the more specific findings. For example, low exposure to statins may be a proxy for reduced healthcare contact. Conversely high exposure may reflect those with increased healthcare contact when Alzheimer’s Type Dementia may be more likely to be detected**.
In the end, this impression is useful in terms of hypothesis generation. However the matter must be settled with data collection and number crunching. In this regards the authors have left researchers with interesting hypotheses that can be tested with relatively small sample sizes (albeit with appropriate power calculations). If these hypotheses are not confirmed then this would merit a more precise mapping out of the assumptions in the model used in this paper.
It should be noted that the statins are not presently licensed for prevention of Alzheimer’s Type Dementia in the UK.
Whenever there are multiple comparisons as in this study, there can be false positives. The usual method for dealing with this is the use of the Bonferonni Correction.
**meaning for instance that cases would be identified earlier and not therefore counted in incident cases
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