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Could the health risks from booze be overblown? A new study has found that low levels of alcohol do not cause cancer, and even heavy drinking doesn鈥檛 cause breast cancer 鈥� contrary to official UK warnings.

The question of how much alcohol it is safe to drink has long been debated. Heavy drinkers are definitely more prone to mouth and throat cancers, and cirrhosis, where the liver starts failing, but it was long thought that light drinking was safe or possibly even good for you.

A growing number of studies, though, have suggested that even low levels of alcohol are linked with a higher risk of cancer, including that of the breast, oesophagus and colon. In 2016, the UK tightened up its alcohol guidelines, cutting the maximum that men should drink from 21 units a week to 14, with the limit for women staying at 14 鈥� equivalent to six pints of beer or just under one and a half bottles of wine.

At the time, the UK鈥檚 chief medical officer, Dame Sally Davies, warned there was 鈥渘o safe level of drinking鈥� and said whenever women had a glass of wine they should weigh up whether it was worth the raised risk of breast cancer.

But the studies that showed these risks from light drinking have a weakness in that they simply look at correlations between drinking levels and cancer rates, and so cannot tell us if alcohol is the cause. Something else could be responsible, as people who drink more also tend to smoke more, have lower incomes, and have unhealthy lifestyles in various other ways.

In the latest work, which has not yet been published, Fotios Drenos and colleagues of Brunel University London in the UK聽got around this problem by analysing genes, which are determined at conception and can鈥檛 be affected by lifestyle influences, like whether聽someone smokes.

They focussed on a gene variant of an enzyme made in the liver that leaves people feeling sick and dizzy after relatively little alcohol. People can have either two, one or no copies of this variant, and those with more copies unsurprisingly tend to drink less.

Drenos鈥檚 team looked at about 300,000 people taking part in a large UK study called Biobank, which has sequenced people鈥檚 genes and periodically surveys their health and behaviour; it has now tracked participants for up to 13 years.

Women who were genetically predisposed to drink more, because of a lower amount of this liver enzyme, didn鈥檛 have a higher rate of breast cancer. In fact, there was no correlation between genes and the likelihood of any type of cancer studied when looking at those who drink less than 14 units a week. However, the team did not study every type of cancer, only breast cancer in women and tumours of the mouth, throat and the rest of the digestive system.

In people who went over this threshold, though, those genetically predisposed to drink more did have a higher rate of throat cancer. 鈥淚t鈥檚 more biologically plausible that heavy drinking causes these tumours as alcohol comes into contact with the throat,鈥� says Drenos.

The team also confirmed the lack of a link with breast tumours in another pre-existing study of genes and cancer, called COGS.

But Frank Dudbridge of the University of Leicester in the UK, who was not involved in the work, says the findings aren鈥檛 the final word, because the cancer risks could be too low to be revealed this way. 鈥淚t鈥檚 difficult to find a small effect unless you have really big datasets.鈥�

And Emmert Roberts of King鈥檚 College London points out that drinking can cause other harms than cancer. 鈥淧hysically, alcohol can affect pretty much every bodily system. Even at low levels, some people might have an increased risk of depression and anxiety.鈥�