Dementia risk still quite low

Written by on June 2, 2016 in in the news, research, What Causes Rosacea? with 0 Comments
rosacea dementia alzheimers

You may have read articles online recently detailing all manner of discoveries relating to how having rosacea can raise your risk of having dementia – twice the chance of Parkinson’s or something like that.

The recent publication of a large study done in Denmark certainly has gained some publicity across the internet. A recent commentary on the Danish study says that 14 news outlets, 3 blogs and 23 tweeters picked up the story. Some of the commentary concluded that there was “7% increased risk of dementia, and a 25% increased risk of Alzheimer’s disease compared with those who didn’t have the skin condition”.

An alternate view

Dr. Leslie Citrome from New York Medical College (and Editor in Chief of the International Journal of Clinical Practice), cautions that reporting on `relative’ versus `absolute’ differences can lead to misleading results.

Rosacea and dementia: relative vs. absolute effect sizes

Int J Clin Pract, June 2016, 70, 6, 428–433.

L. Citrome New York Medical College, Valhalla, NY, USA

The difference in crude rates failed to show that the rate of Alzheimer’s disease was greater in women with rosacea.

When calculating the difference in incidence rate/1000 person years, rates for Alzheimer’s disease were indeed higher for women with rosacea, and amounted to an absolute risk increase of 0.19/1000 person years. This latter result leads to substantially less alarm than stating a 28% increase in risk.

Relative measures of effect size are prone to misinterpretation by the lay press because they seem so large although the absolute rates they are calculated from are quite small.

Moreover, in observational studies, many epidemiologists will be less likely to accept at face value a relative effect size of less than 3.0, and almost never a relative effect size of less than 2.0. Increases in risk of less than 100% (i.e. a relative effect size of less than 2.0) are difficult to interpret because of the possibility of confounding factors that have not been accounted for.

(emphasis added).

Putting Results in Perspective

So what does an `absolute risk increase of 0.19/1000 person years’ mean? If this is indeed the more considered output of the Danish research, what sort of increased risk is there, for real?

Well it would take around 5000 person years to find one more person with dementia that also has rosacea. So if we say we will live to 80, that means just 1 more person per 65 persons develops dementia co-incidence with their rosacea. Doesn’t sound so bad as “double the risk or dementia” now does it ?

A Professional Rebuke

Dr. Citrome goes on to chastise the original researchers for going for the `big news’ headline rather than the more conservative, and equally accurate story that the `risk is still quite low’.

Upon interview, the lead author has stated ‘In fact, while the risk in rosacea patients may be slightly increased compared with the general population, the absolute risk [to any one patient] is still quite low’.

However, it would have been best if that statement was placed in the published report and abstract, and in the accompanying press release, thus avoiding stoking fears among those with rosacea that their true risk of developing dementia is much higher than what the research actually suggests.

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About the Author

About the Author: David Pascoe started the Rosacea Support Group in October 1998. .

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