Current guidelines may be too high
The relationships between alcohol consumption and aspects of health are sometimes controversial. In fact, many longitudinal studies show that low to moderate alcohol intake predicts reduced risk of premature death and cardiovascular disease. Governmental agencies and other organizations recommend upper limits for weekly or daily alcohol consumption. Recent studies suggest that those recommendations may be too high. For example, a huge multinational project undertaken by the Emerging Risk Factor Collaboration using data from three large studies including 599,912 current drinkers of alcohol in 19 high-income countries concluded that about 100 grams of alcohol per week (equivalent to one standard alcoholic drink per day) comprised the threshold for the lowest risk of all-cause mortality. For cardiovascular disease subtypes (aside from myocardial infarction), no clear threshold existed below which increased alcohol consumption ceased being linked with lower disease risk. Official recommendations for limiting alcohol consumption generally exceed what these data suggest.
Shortcomings of past studies may explain the cardioprotective effect of limited alcohol intake
Some longitudinal studies show that low to moderate alcohol consumption, compared to high or no alcohol consumption, predicts lower risk of mortality. In fact, some healthy eating scoring systems penalize participants who abstain from any alcohol consumption. However, more recent studies have found negative outcomes for any amount of alcohol intake. A new systematic review and meta-analysis of 107 cohort studies corrected for publication bias (studies that show no significant differences may not get published), heterogeneity among studies (arising from different mythologies, participants with differing ages, ethnicities, or races, and different statistical techniques), and accounting or not for confounding factors that might affect the outcomes of studies of alcohol intake and mortality. The meta-analysis did not find that low or moderate alcohol intake significantly predicted mortality risk. That said, increased risk appeared at higher levels of alcohol intake (three or more drinks per day), more so for women than men.
Low levels of alcohol intake and hypertension
Reducing high blood pressure reduces the risk of cardiovascular disease more than any other modifiable lifestyle behavior. Yet the relationship between low to moderate levels of alcohol consumption and risk of hypertension remain unclear. A team of researchers shed light on this matter with a meta-analysis of seven longitudinal cohort studies in which participants were followed for a median of 5 years. Analyses revealed a nearly linear relationship between systolic blood pressure and daily alcohol intake ranging from 0-50 grams per day for both men and women. A standard alcoholic drink, such as, one can of beer, has about 14 grams of alcohol. Daily intake of 14 grams of alcohol predicted a 1.25 mm Hg increase in systolic blood pressure. The increase in systolic blood pressure with increasing alcohol intake was steeper for men than women. Thus, this study found no threshold below which higher alcohol consumption reduced systolic blood pressure. The relationship between alcohol intake and diastolic blood pressure was curvilinear with progressively less increase in systolic blood pressure as daily alcohol intake increased. Even a small decrease in systolic blood pressure arising from reducing daily alcohol intake by one standard drink might lower risk of mortality across large populations.
Bias might account for alcohol's cardioprotective effect
Numerous longitudinal cohort studies show a cardioprotective link of low to moderate levels of alcohol intake compared to either abstinence from alcohol or from high levels of alcohol intake. Bias might account for the cardioprotective effect, because research subjects who report limited alcohol intake may be healthier by engaging in healthier behaviors than subjects who report no alcohol intake. Given the ethical and practical difficulties of long-term randomized clinical trials, a recent study used a statistical technique, mendelian randomization, to circumvent issues of confounding and reverse causation. Data came from 371,463 participants in the UK Biobank with an average age of 47 years. The average participants consumed 9.2 alcoholic drinks per week—in the light to moderate range.
Standard analysis of the data showed the expected result of significantly lower risk of developing cardiovascular disease (specifically, hypertension and coronary artery disease) for participants in the light to moderate alcohol intake range over up to 10 years of follow-up. However, these same participants had significantly better self-reported health and lower rates of smoking, lower body-mass index, higher physical activity, and higher vegetable intake compared to participants with zero alcohol intake. After adjustment for these factors, the strength of the link between low to moderate levels of alcohol intake and risk of cardiovascular disease diminished, often to statistical non-significance. Mendelian randomization analyses showed an upward curvilinear increase in risk of cardiovascular disease with increasing alcohol intake. The data showed no cardioprotective effect of low to moderate alcohol intake. Increasing alcohol intake from 0 to 1 drink per day showed a minimal, but statistically significant, increase in cardiovascular disease risk. Beyond 2 drinks per day, the risk of cardiovascular increased dramatically to nearly 20 times higher for 4 or more drinks per day.
What to do?
A prudent response to the above studies would be to limit your alcohol intake to one drink per day. If you don't consume alcohol, don't start. Another prudent response would be to cut back substantially on alcohol if you regularly have 4 alcoholic drinks per day.
