Mendelian meta-analysis and the alcohol “flush” allele.
Less than a year after the massive Mendelian randomization meta-analysis published in the British Medical Journal, a group of researchers recently wrote an editorial in the journal Addiction, which would seem to put a lid on the matter:
The foundations of the hypothesis for protective effects of low-dose alcohol have now been so undermined that in our opinion the field is due for a major repositioning of the status of moderate alcohol consumption as protective…. Health professionals should not recommend moderate alcohol consumption as a means of reducing cardiovascular risk for patients. At the policy level, the hypothesis of health benefits from moderate drinking should no longer play a role in decision making.
To recap: In the Mendelian meta-analysis, drinkers with a genetic variant linked to the so-called alcohol flush reaction, which leads to lower consumption among those who drink, also correlated with a decreased risk of cardiovascular disease. “Carriers of the rs1229984 A-allele had lower levels of alcohol consumption and exhibited lower levels of blood pressure, inflammatory biomarkers, adiposity measures, and non-HDL cholesterol, and reduced odds of developing coronary heart disease, compared with non-carriers of this allele.”
But as it turned out, this relationship only held for drinkers, not for abstainers.
Why, then, have so many epidemiologists agreed for several decades now that “moderate” alcohol intake has a protective effect against heart diseases? According to the editorial authors—drug researchers from Australia, Canada, the U.S., and Sweden—earlier research tended to use “abstainers” as the key reference group to which drinkers were compared. Studies that separated former drinkers and occasional drinkers from abstainers got different results—they didn’t show significant protection correlating with moderate alcohol consumption. The theory, say the researchers, is that non-addicted drinkers spontaneously reduce their alcohol intake with age and medical concerns. Some of these people with a declining health profile are counted as “abstainers.” But when former and current drinkers are combined, then compared with life-long abstainers to address selection bias, “the observed disparity in health status between abstainers and low-dose drinkers was eliminated.”
But it’s not quite over. Michael Rioerecke and Jurgen Rehm at the Center for Addiction and Mental Health in Toronto, argue in another Addiction editorial that there are still a few things unaccounted for: The allele in question is assumed to be randomly spread throughout the population, which may or may not be true, especially since allele carriers are relatively rare in several European countries. The allele is also assumed to be mediated by average alcohol intake. Binge drinking, which allele carriers presuming engage in less, is not assessed in the study. In short, they write, “we do not know if the average level of alcohol intake of the allele carriers within the strata of average consumption was indeed lower than that of the non-carriers.” Nonetheless, even Rioerecke and Rehm concede that the evidence continues to look promising for this revision of conventional drinking wisdom. More than 100 studies have shown relatively stable associations between alcohol and heart disease, and absent a new breakthrough method of epidemiological study, this one stands a good chance of holding firm.
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