August 23, 2015

Homocysteine, Cognition And Dementia - A Consistent Association

What do we mean by 'consistency'?

In this blog post we continue our review of the association between high blood levels of homocysteine and cognition. We are considering the link in terms of 'causality,' and how this relates to the work of Sir Austin Bradford Hill.

Hill considered that an important feature of a causal link would be whether it is 'consistent' or not. By this, he meant whether different persons, in different places, circumstances, and times, repeatedly observed the same association.

A consistent association:

Hill suggested that a good guide to a consistent association would be whether similar observations were reached in different ways. For example, is the relationship seen in studies following how the association develops over time (i.e. 'prospective' studies) as well as those looking back at historic data (i.e. 'retrospective' studies)?

Using this criteria, the relationship between high homocysteine and cognitive decline, as well as dementia, is certainly very consistent!

By 2008, 77 cross-sectional studies on more than 34,000 subjects and 33 prospective studies on more than 12,000 subjects had reported associations between homocysteine and cognitive deficit or dementia!


In our next Blog update, we will look at whether the link between homocysteine and cognition is 'specific', and related to memory impairment alone.


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