Just one glass of fruit juice or fizzy drink a day significantly raises the risk of cancer, a major study suggests.
Experts last night warned that people are being 'conned' into thinking 'natural' fruit juice is healthy - even though it is packed with sugar.
Researchers found every 100ml serving of pure fruit juice consumed each day- whether freshly squeezed or sold in a bottle - increases the odds of developing cancer by 12 per cent.
And drinking the same volume of sweetened soft drinks - such as cordial or fizzy pop - increases cancer risk by 19 per cent.
Doctors said the study - which tracked more than 100,000 people in France - strengthens the case for robust Government action to cut consumption of sugary drinks.
But the findings come after Tory leadership contender Boris Johnson last week said he may reverse Theresa May's flagship sugar levy on soft drinks, belittling such measures 'sin stealth taxes'.
Health officials are increasingly concerned about UK sugar consumption, particularly among children.
Sugar intake is nearly three times the recommended limits for people of all ages, according to Public Health England figures.
And soft drinks are the biggest source of sugar in the diet of children and teenagers, providing 33 per cent of sugar intake for 11-to-18-year-olds - which ministers admit is among the highest level in Europe.
This includes fruit juice, which makes up 10 per cent of sugar intake for this age group.
The researchers, from the Sorbonne in Paris and the French Public Health Agency, said strong policies to cut intake of sweet drinks could even cut cancer rates.
The researchers proposed some biological mechanisms to explain how fizzy drinks could lead to an increased risk of cancer.
Based on previous research, it could be because sugar adds to fat stored around vital organs such as the liver and pancreas, which leads to the growth of tumours, even if the person is of a health weight.
The glycaemic load also has an effect on blood sugar levels and inflammatory markers, both of which are linked to increased cancer risk.
It may be related to obesity, which is a well-known risk factor for various types of cancer.
The findings add to an overall picture of the importance of the current drive to reduce our sugar intake, due to excess sugar being a key driver in many health issues - diabetes, obesity and tooth decay, for example.
The academics, writing last night in the British Medical Journal, said: 'These data support the relevance of existing nutritional recommendations to limit sugary drink consumption, including 100 per cent fruit juice, as well as policy actions, such as taxation and marketing restrictions targeting sugary drinks, which might potentially contribute to the reduction of cancer incidence.'
They added: 'Of note, despite their overall healthy and natural image in the general population... 100 per cent fruit juices generally contain high levels of simple sugar - 10.3 g/100 mL in this study, sometimes higher than regular soda.'
The team tracked 101,257 people who were aged 42 on average at the start of the study and were followed up for an average of five years.
Their intake of more than 3,000 different food and drink items was assessed at the start of the study and every six months, with each person completing at least two 24-hour dietary questionnaires.
The results showed that for each 100ml per day, a person's cancer risk increased by 18 per cent.
For fruit juice the increase was 12 per cent and for sugar-sweetened drinks it was 19 per cent. Artificially sweetened drinks, such as diet pop, resulted in no increased risk.
Experts last night criticised the marketing of fruit juice around the world as a 'healthy' product - warning that the drinks are packed with sugar, whether they are added artificially or not.
Professor Nikolai Petrovsky, of Flinders University in Australia, said: 'The population continues to be conned into thinking that "natural" automatically equates to "healthier" which is simply not the case.
'High sugar natural fruit drinks, which are flourishing worldwide and being marketed as a "healthier" option' by juice and smoothie companies, can be just as bad if not worse than the carbonated drinks they are attempting to replace, as in many cases they can have an even higher total sugar content.'
Obesity is a known cause of 13 different types of cancer but the new study found even slim people were at increased risk if they drank sugary drinks or fruit juice.
The team said being overweight 'might not be the only drivers of the association between sugary drinks and the risk of cancer'.
They pointed to other research which suggested that sugary drinks promoted body fat around the abdomen, even if a person is of a healthy weight, which in turn promotes the growth of tumours.