A New Zealand university review has found strong evidence that alcohol causes at least seven types of cancer.

There is strong evidence that alcohol causes seven types of cancer and probably others, a review has concluded.

A study of existing research found strong evidence of a direct, harmful effect of drinking, even though scientists are unsure of the exact biological reasons why alcohol causes cancer.

Writing in the journal Addiction, Jennie Connor, from the University of Otago said alcohol is estimated to have caused about half a million deaths from cancer in 2012 alone - 5.8 per cent of cancer deaths worldwide.

The highest risks are from heavy drinking, but even people who drink at low levels are at risk.

Her review linked alcohol to cancer of the mouth and throat, larynx, oesophagus, liver, colon, bowel and breast.

"There is strong evidence that alcohol causes cancer at seven sites, and probably others," she said.

"Confirmation of specific biological mechanisms by which alcohol increases the incidence of each type of cancer is not required to infer that alcohol is a cause."

She said that based on current evidence, there is no safe level of drinking with respect to cancer though the risks are reduced for some cancers when people stop drinking.

She added that the supposed health benefits of drinking - such as red wine being good for the heart - were "seen increasingly as disingenuous or irrelevant in comparison to the increase in risk of a range of cancers".

Scientists are still researching how alcohol can lead to cancer. One theory is that alcohol damages DNA.

Many people believe that alcohol consumption is only linked to liver cancer, but the Otago review confirms other research that shows alcohol is strongly linked to an increased risk of a number of different cancers, says Susannah Brown, science program manager for the World Cancer Research Fund.

"For cancer prevention, we have long recommended that people should not drink alcohol at all, but we understand that this can be easier said than done."