Health evidence: quality vs quantity
From the Sunday Star-Times, on fish oil
Grey and colleague Dr Mark Bolland studied 18 randomised controlled trials and six meta-analyses of trials on fish oil published between 2005 and 2013. Only two studies showed any benefit but most media coverage of the studies was very positive for the industry.
On the other hand, the CEO of a fish-oil-supplement company disagrees
Keeley said more than 25,000-peer reviewed scientific papers supported the benefits of omega-3. “With that extensive amount of robust study to be then challenged by a couple of meta-analyses where negative reports are correlated together dumbfounds me.”
In fact, it happens all the time that large numbers of research papers and small experiments find something is associated with health then small numbers of large randomised trials show it doesn’t really help. If it didn’t happen, medical and public health research would be much faster, cheaper, and more effective. I’m a coauthor on at least a couple of those 25000 peer-reviewed papers, and I’ve worked with people who wrote a bunch more of them, and I’m not dumbfounded. You don’t judge weight of evidence by literally weighing the papers.
Mr Keeley takes fish oil himself, and believes he will “live to 70, or 80 or 90 and not suffer from Alzheimer’s.” That’s actually about what you’d expect without fish oil. He’s 60 now, so his statistical life expectancy is another 23 years, and by 83, less than 10% of people have developed dementia.
I wouldn’t say there was compelling evidence that fish-oil capsules are useless, but the weight of evidence is not in favour of them doing much good.
Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient See all posts by Thomas Lumley »
I particularly like the second sentence:
“My heart is 50 years old, according to my doctor,” the 93-year-old Papakura woman says.
So has she had a heart transplant?
10 years ago
That *is* the sort of thing doctors say — there’s even been some research on defining ‘arterial age’ sensibly.
10 years ago
Anyone remember getting this http://en.wikipedia.org/wiki/Lane%27s_Emulsion as a child? I do.
The notion that fish is good for brain development has been around for over a century. Till shown otherwise I’d still make sure the kids got plenty of fish oil one way or another.
Any idea on the benefits of oily fish as opposed to fish oil in isolation?
10 years ago
Most of the supportive observational evidence is for oily fish rather than capsules.
These fatty acids are important for infants — they’re found in breast milk and added to infant formula — but the old reason for cod liver oil supplements in older kids was vitamin A and D shortage. These vitamins are now added to milk (in NZ, only some milk), which is more palatable.
10 years ago
Just published: http://www.ajpmonline.org/article/S0749-3797%2814%2900257-8/abstract
“Dietary consumption of baked or broiled fish is related to larger gray matter volumes independent of omega-3 fatty acid content.”
In other words – fish is brain food regardless of the omega-3.
10 years ago
Meh. Firstly, that’s dementia, where there has never really been any good evidence for fish oil.
Second, I’m not convinced by the analysis. Since omega-3 intake was estimated from fish consumption, it has strictly larger measurement error, so it’s not all that surprising that a regression model prefers the fish consumption data.
And third, fish consumption could easily just be a marker for other lifestyle differences. I’m a bit surprised that the paper isn’t more careful with words like ‘effect’, given some of the people involved.
10 years ago