Why doctors don’t like J-curves
Last week’s Stat of the Week nomination was a story on the “J-curve” for disease risk and alcohol consumption. Yet another research paper, this time from the Nurses’ Health Study, had found that people who drink small amounts of alcohol regularly are healthier than those who drink none and those who drink larger amounts. This sort of result is unpopular with doctors, as the Herald story reported, and for good reasons, but that doesn’t mean it’s untrue. On the other hand, the fact that it’s true doesn’t mean that it’s news.
The obvious difficulty in comparing drinkers to non-drinkers is that some of the strictest non-drinkers are actually ex-drinkers, people who you would expect to be in worse health. Since epidemiologists are not completely stupid, they know about this problem and many studies have addressed it. Excluding ex-drinkers doesn’t make the effect go away, waiting for a long time between the drinking assessment and the health assessment (as in this paper) doesn’t make it go away, and splitting up light drinking into finer categories shows that there is lower risk for people who drink occasionally than for those who regularly drink a small amount (again, as in this paper). For some of the claimed benefit there are even plausible mechanisms (eg, alcohol consumption does definitely raise HDL cholesterol levels in short-term experimental studies). This is just observational research, so the results could be just as wrong as the apparent protective effect of beta-carotene in cancer, or of raising HDL cholesterol with niacin in heart disease, which fell apart when subjected to randomised trials, but it’s carefully-done observational research.
As doctors will tell you, the problem with announcing a health benefit of moderate alcohol consumption is that most people interpret “moderate” to mean “a bit more than I currently drink”. As a scientific result, it’s fine; as a public-health intervention, it’s badly off-target. The American Heart Association guidelines on alcohol and heart disease, for example, basically say that regular consumption of small amounts of alcohol probably is protective against heart disease, but that you shouldn’t go around advocating it.
The problem for medical researchers is that funding bodies and universities (and their own egos) want press coverage of research results, but that this sort of marketing of incremental medical research as if it was ground-breaking health advice is unhelpful to the public. It’s very rare that you should change your behavior based on the results of a single medical study, but that’s the model that a lot of medical reporting is based around.
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 wish that the MoH here would just tell the truth about the J-Curve. Governments oughtn’t engage in lies, no matter how noble the intentions. They could easily say “For most people, drinking one or two standard drinks per day reduces mortality risk. People with family history of alcoholism should avoid drinking, but people with family history of heart disease should avoid abstaining. Drinking more than four standard drinks per day is a bad idea.” The NZ Ministry of Health is either staffed by people who are incompetent at reading the literature or who lie about the results. Neither is good.
I figure, but without particular evidence, that if folks got into the habit of having a glass of wine with dinner, every night, and got the kids into the habit of having a single glass with dinner in their teens, it would do a lot to teach kids about responsible drinking. That’s what we’ll be aiming for with ours anyway. It’ll be more than a few years before the three year old is ready though.
13 years ago
I work in health too – a DHB, and I think the whole mis-reporting thing is also to do with bigwigs who aren’t statistically literate and don’t care to educate themselves or to listen to those who are, and just want some important looking numbers to wave around.
13 years ago
If you look at table 2 in the nurses paper, it looks like there is a dose-response relationship between alcohol and “successful aging” i.e. the more you drink the more likely you are to successfully age. What???? The top drinking group is 2-3 drinks per day (not per drinking occassion) yet 4 drinks per drinking occassion is considered hazardous for women (and they are mostly women).
And then you find out that they chucked out over 2000 people at baseline because they were already un-“successfully aging”.
Altogether it smells like survivorship bias. The effect of alcohol caused the “less healthy” people in the alcohol use group to not make it into the analysis group because they’d already failed by baseline. The “less healthy” in the non-alcohol group weren’t eliminated in the same way because they didn’t use alcohol. It means the alcohol use group were a hardier cohort than the non-alcohol use group.
(And they accounted poorly for socio-economic status of the family unit – education doesn’t cut it.)
11 years ago