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A paper published in the BMJ has examined the effect of alcohol on the health of various age groups. They analysed mortality and report that previously beneficial effects of alcohol may be strongest in women of over 65. A Before the Headlines analysis accompanied these roundup comments.
Dr Mike Knapton, Associate Medical Director at the British Heart Foundation, said:
“This study suggests any protective effect of alcohol is limited to women aged over 65. There was little or no benefit observed in other age groups or men.
“Guidelines on drinking alcohol recommend that men should not regularly drink more than three to four units of alcohol a day and women should not regularly drink more than two to three units of alcohol a day.
“If you don’t drink we wouldn’t advise you to start as any benefit to your heart from alcohol is limited.
“There are safer and healthier ways to protect your heart such as doing more physical activity, eating a healthy, balanced diet and stopping smoking.”
Prof. Paul Pharoah, Professor of Cancer Epidemiology, University of Cambridge, said:
“This paper reports on a study based on over 18,000 people aged over 50 who took part in the Health Survey for England between 1998 and 2008. Participants were asked questions about their alcohol intake and then followed-up for approximately 10 years on average.
“The investigators evaluated the association between self-reported alcohol consumption and death from any cause. The associations were evaluated separately for men and women and for age 50-64 and age 65+.
“Overall the findings of this study are in broad agreement with what has been previously published – despite what is written in the press release.
“The main findings were that there was a reduction in mortality in almost all categories of alcohol consumption (main number reported in the results table is the relative hazard. A relative hazard of < 1 is a protective effect). For some of the categories this finding was statistically significant and not in others. The investigators make too much of these differences in nominal statistical significance. While some results were statistically significant and others not, the consistency of the findings in the different age/sex groups is more striking. I do not agree with their conclusion that “Little to no protection was found in other age-sex groups, regardless of consumption level”. Because there were 10 different alcohol consumption groups being evaluated the number of deaths in each group was fairly small – particularly in the non-drinker reference group – and the statistical power to detect modest effects will have been small.
“In short the findings – although not statistically significant in part – were fairly consistent with previously reported research in which moderate alcohol consumption has been associated with a modest reduction in mortality.
“There was very little difference between the models that adjusted only for age (model 1 in the Tables) and models that adjusted for a variety of possible confounders, but many other possible confounders were not measured and could not be accounted for.
“The effects were also reduced, particularly in women aged 50-64, when drinkers were compared to never drinkers rather than current non-drinkers (the latter category including former drinkers). There appeared to be little difference in the findings comparing men with women.
“The authors are correct in pointing out the need for caution in interpreting these data. Association does not mean causation. This is an observational study and there are all sorts of biases that might result in a association between alcohol consumption and reduced mortality that is not causal. These include difficulties in measuring alcohol consumption, the likelihood that other factors such as diet and exercise that are associated with alcohol consumption could not be controlled for in these analyses, and the likelihood that alcohol consumption may depend on the presence of pre-existing illness.
“In summary, I do not think these results provide any major new insights into the complex relationship between alcohol consumption and risk of death and they provide no evidence that current guidelines on reasonable alcohol intake are inappropriate.”
Prof. Kevin McConway, Professor of Applied Statistics, The Open University, said:
“The problem here is that there just aren’t all that many lifetime non-drinkers in these samples, particularly amongst the men, and not many of them died, so the mortality rates for lifetime non-drinkers can’t be estimated very accurately. The study then involves comparing these rather imprecisely estimated rates with the mortality rates for various groups of drinkers. The resulting relative risks are therefore also not known very precisely. So generally the data are compatible with the possibility that there is a protective effect of the sort of size suggested previously, and in several of the comparisons, the data are at the same time compatible with there being no protective effect, and indeed with many other possibilities. With these data and this method of analysis, there simply isn’t the statistical power available to decide which of these possibilities is true.
“We shouldn’t instantly jump to the conclusion that, in underpowered comparisons like these, lack of statistically significant evidence for a protective effect means that there definitely isn’t a protective effect.”
Prof. Sir David Spiegelhalter, Winton Professor of the Public Understanding of Risk, University of Cambridge, said:
“The authors’ conclusions are not backed up by the data. All groups consuming less than 20 units a week experienced lower mortality rates than the lifelong teetotalers. But since there are not many teetotalers, there is large uncertainty about what the true underlying relative risks are. All the observed data are compatible with the kind of 15 to 20% protection that has been previously suggested, and the authors are not justified in claiming there is no protection apart from some specific groups.
“Essentially, the study is grossly underpowered to convincingly detect a plausible protection, and they have committed the cardinal sin of saying that non-significance is the same as ‘no effect’ in a study lacking sufficient events, in this case, deaths in non-drinkers. This is a poor use of statistics, and I am surprised it got past the referees.”
Prof. Timothy Spector, Professor of Genetic Epidemiology, King’s College London, said:
“Overall this observational study found like other large meta-analyses before it – a slight protective effect of moderate alcohol drinking on risk of death, with the strongest benefit in women over 65 – but a suggestion here that much of the benefit could be due to a limitation of the methods, misreporting and selection bias.
“The study sadly lacked clear heart risk data which alcohol is said to benefit. While some alcohol like wine contains potentially important nutrients and polyphenols – and appears safe in small amounts – we should be cautious about promoting it as a health drink until we have better evidence. The queen mother may have been helped by her genes, alcohol or luck- we still don’t know for sure. ”
Dr Tim Chico, Reader in Cardiovascular Medicine / consultant cardiology, University of Sheffield, said:
“On the face of it, this should be an easy question to answer, but sadly it turns out it isn’t that simple at all.
“The authors have access to surveys where thousands of people have stated how much and often they drink, and followed up through their health records to see whether they die. Similar studies have often suggested moderate amounts of alcohol intake reduces risk of cardiovascular disease such as heart attack, although the current study only looked at risk of death from all causes rather than trying to look for a specific “heart-healthy” effect. One of the problems of such studies is that people inaccurately report their alcohol intake, often wildly so. Another difficulty is knowing who to consider as “non-drinkers”. Many studies have included previous drinkers in this group, but that is a problem if they have given up because their health is already affected by alcohol. The current study tries to compare drinkers against people who say they have never drunk alcohol in their life (so-called “never-drinkers”). When drinkers are compared with “never-drinkers” there was much less evidence of a protective effect of alcohol, limited to younger men drinking 15-20 units/week or women over 65 drinking up to 10 units/week.
“When talking about the benefit of any drug (whether this be alcohol, statins, or aspirin) this always needs to include a discussion of the risks all drugs have. The negative effects of alcohol are obvious, cause huge drains on the health system, and clearly outweigh any possible benefits.”
‘All cause mortality and the case for age specific alcohol consumption guidelines: pooled analyses of up to 10 populations based cohorts’ by Knott et al. published in The BMJ on Tuesday 10th February.
Declared interests
Dr Mike Knapton has 40 shares in Adnams Co – http://adnams.co.uk/
Prof. Sir David Spiegelhalter is providing comments to the current Chief Medical Officer’s Review of Alcohol Guidelines
No other interests declared