How many drinks is really too many? Too much alcohol damages DNA in ways linked to developing Alzheimer's, cardiovascular disease

New research sounds the alarm over over anything more than five large glasses of wine. Photo / 123RF

The answer to the age-old question of "how many drinks is really too many" is anything more than five large glasses of wine a week, according to scientists from the University of Oxford

In the short term, a handful of pints of beer an evening is known to make itself felt the next day, but scientists have never before looked at how alcohol affects our long-term ageing process.

Oxford academics have now found out the limit is 17 units, or roughly five large glasses of wine or five pints of lager a week.

Any more than this and it starts to take its toll on our DNA, affecting the caps on the end of our chromosomes called telomeres.

Damage to these areas has previously been linked to Alzheimer's and cardiovascular disease. People with healthier, longer telomeres are also thought to have longer lifespans.

Data from almost half a million people enrolled in the UK Biobank was used. The team looked for tell-tale genetic markers which show how much alcohol a person drinks. Their telomere length was measured in a laboratory after taking DNA from a swab.

The scientists found that a small amount of alcohol does not affect our DNA, but beyond the 17-unit threshold this changes and our telomeres come under attack.

The top 40 per cent of drinkers – who consumed more than 17 units of alcohol a week – were found to have some telomere shrinkage caused by alcohol consumption.

However, the remaining 60 per cent of people, who drink less than 17 units a week, were found to be genetically undamaged.

Someone who drinks 32 units per week, or about 10 large glasses of 13 per cent ABV wine, is biologically three years older than someone on 10 units a week (roughly three large glasses of wine), for example.

'Necessary minimum amount'

But the research found no link between alcohol consumption and biological ageing below the 17-unit threshold, with someone having one dram of whisky a week as unaffected as someone who has a glass of wine every week night.

"This finding suggests that a necessary minimum amount of alcohol consumption is required to damage telomeres," the researchers write in their study, published in Molecular Psychiatry.

"Similar relationships with alcohol have been described for other health outcomes," they add.

Exactly how alcohol intake is linked to telomere damage remains unknown and this study does not provide causal evidence but does show a strong observational connection.

One potential harmful mechanism suggested is that the breakdown of alcohol molecules leads to oxidative stress and inflammation which are hazardous to DNA.

"These findings support the suggestion that alcohol, particularly at excessive levels, directly affects telomere length," said study lead Dr Anya Topiwala from Oxford Population Health.

"Shortened telomeres have been proposed as risk factors which may cause a number of severe age-related diseases, such as Alzheimer's disease.

"Our results provide another piece of information for clinicians and patients seeking to reduce the harmful effects of excess alcohol. Furthermore, the dose of alcohol is important – even reducing drinking could have benefits."

'Clear links with ageing'

Dr Richard Piper, chief executive of Alcohol Change UK, welcomed the results.

He said: "This particular study shows clear links between consuming alcohol and ageing, and points towards a possible link between alcohol and Alzheimer's.

"The researchers are transparent that this study does not prove a causal link, but they also make a well-argued case about the likely biological mechanism.

"In general, there is an ever-larger body of science showing how, exactly, alcohol causes so much ill-health and so many early deaths."

The NHS recommends people do not drink more than 14 units a week and that this should be spread over at least three days to avoid binge-drinking.