A wise man once said ‘as we know, there are known knowns; there are things we know we know. We also know there are known unknowns; that is to say we know there are some things we do not know. But there are also unknown unknowns – the ones we don’t know we don’t know.’
A major advance in clarifying our knowledge base has been made in the development of the Cochrane Library online (www.cochranelibrary.com) which I heartily recommend to readers. The site regularly publishes reviews of all the current published evidence and comments on its strength in proving a particular concept. It has also developed a bias risk tool which helps to decide upon the objectivity of published claims in the literature.
The site is not without critics, and many argue that the focus on high level randomised control study evidence overshadows other findings where human variation and multifactorial influences, for example, are hard to control and play a part in dictating the nature of study.
That said, I find it useful to access regularly as a reality check, as I did last week. I often hear colleagues recommending or advising others to recommend nutritional supplements to either prevent age related macular degeneration or to reduce the risk of its onset. Here are two quotes from reviews published last month:
‘Supplements containing lutein and zeaxanthin are heavily marketed for people with age-related macular degeneration but our review shows they may have little or no effect on the progression of AMD.’
‘Taking vitamin E or beta-carotene supplements will not prevent or delay the onset of AMD. The same probably applies to vitamin C and the multivitamin (Centrum Silver) investigated in the one trial reported to date. There is no evidence with respect to other antioxidant supplements, such as lutein and zeaxanthin.’
We do not need to agree with Rumsfeld.