Alcohol may raise blood pressure more than thought

The new research, published in PLoS Medicine​, follows calls from the European Commission last year that drinks makers must do more tackle excessive drinking has cast the issue into the spotlight and put the industry on its toes. A British government report from 2006 reported that almost half of men and more than a third of women aged 16-24 already drink more than their daily allowance, increasing their risk of health problems such as cirrhosis later in life. The Bristol-based researchers aimed to ascertain a clearer correlation of alcohol intake to blood pressure than had been achieved to date. Observational studies that ask people about their drinking habits cannot provide a causal link partly because other risk factors, such as diet or smoking might affect blood pressure. Clinical trials are difficult to implement and have a limited follow-up time. In this study the researchers used Mendelian randomisation, meaning that they made use of measured variation in a specific gene. Alcohol is initially metabolised to an intermediate compound called acetaldehyde which is further metabolised and eliminated from the body. The enzyme mostly responsible for elimination is aldehyde dehydrogenase 2 (ALDH2). An inactive variant of ALDH2 has been identified. People who inherit the variant form of this gene from both parents have an ALDH2*2*2 genotype (genetic makeup). They are unable to metabolise acetaldehyde. After drinking they become flushed, nauseous and suffer other unpleasant symptoms. Naturally therefore, people with *2*2 genotype drink less than people with a *1*2 genotype who have a limited ability to metabolise acetaldehyde, who in turn drink less than people with a *1*1 genotype, who can drink relatively heavily. Inheritance of these genetic variants does not affect lifestyle factors other than alcohol intake, so an association between ALDH2 genotypes and blood pressure would indicate that alcohol intake has an effect on blood pressure without confounding. The researchers identified ten published studies on associations between ALDH2 genotype and blood pressure or hypertension, mainly from Japan where the ALDH2 variant is common. A meta-analysis (method for combining the results of studies) of the studies that had investigated the association between ALDH2 genotype and hypertension found that men with the *1*1 genotype (who could drink relatively easily) were 2.42 times more likely to have hypertension than those with the *2*2 genotype. Men with the *1*2 genotype were 1.72 times more likely to have hypertension than those with the *2*2 genotype. A second meta-analysis of relevant studies showed that systolic and diastolic blood pressures exhibited a similar relationship to ALDH2. The researchers estimated that for men the lifetime effect of drinking 1g of alcohol a day: "would be an increase in systolic blood pressure of 0.24mmHg​." "This study shows that alcohol intake may increase blood pressure to a much greater extent, even among moderate drinkers, than previously thought. Large-scale replication studies are required to confirm this finding and to improve the precision of our estimates​." The report confirmed that high blood pressure (hypertension) affects nearly a third of US and UK adults. It can lead to heart attacks or strokes. Normal blood pressure is defined as a systolic pressure of less than 130 millimetres of mercury (mmHg) and a diastolic pressure of less than 85mmHG (blood pressure of 130/85). A reading of more than 140 / 90 indicates hypertension. The researchers were affiliated with the Department of Social Medicine, University of Bristol, UK and the Medical Research Council Centre for Causal Analyses in Translational Epidemiology, University of Bristol, UK. Source: Public Library of Science journal, PLoS Medicine "Alcohol Intake and Blood Pressure: A Systematic Review Implementing a Mendelian Randomization Approach​" Authors: L. Chen, G. Davey Smith, R.M. Harbord, S.J. Lewis