Drinking just two sugary drinks a day may double a woman's risk of developing bowel cancer before she turns 50, research suggests.
Regularly indulging in high-sugar sodas has long been linked to obesity and type 2 diabetes, however, its effect on cancer was less clear.
Bowel cancer is on the rise among young people. In the US, adults born in the 1990s are said to face up to four times the risk of the disease as those born four decades earlier.
With this coinciding with a rise in soda consumption, scientists from the Washington University School of Medicine in Missouri analysed more than 95,000 female nurses, who provided information on their diet every four years for nearly a quarter of a century.
Results suggest the women who drank two or more sugary drinks a day were over twice as likely to develop bowel cancer before they turned 50 than those who indulged less than once a week.
Although it is unclear, sugary sodas may reduce feelings of fullness, causing people to overeat. Carrying excess weight has been linked to cancer.
Other experts have stressed, however, the study was relatively small and should be interpreted with caution.
This comes after scientists from Zhengzhou University in China recently reported diet drinks are no healthier than sugary sodas.
About 42,000 people are diagnosed with bowel cancer every year in the UK.
Early-onset forms of the disease, defined as a patient being under 50, have "been on the rise in many high-income countries over the past two decades", the Washington scientists wrote in the journal Gut.
In the US, adults born around 1990 are twice as likely to develop colon cancer – beginning in the large intestine – as people who are 40 years their senior.
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The risk rises by four times when it comes to rectal tumours, which specifically affect the last few inches of the large intestine. Bowel cancer is a generic term for tumours affecting the large bowel, which includes the colon and rectum.
Sugary beverages – whether soft, fruit, sports or energy drinks – are the leading source of added sugar in the US diet, with more than one in 10 (12%) consuming over three servings a day.
From 1977 to 2001, consumption of these drinks more than doubled among people aged 19 to 39.
To better understand any link between sugary drinks and bowel cancer, the Washington scientists analysed participants of the Nurses' Health Study II, who were aged 25 to 42 at the start of the trial in 1989.
From 1991, the women reported what they ate and drank via a questionnaire every four years.
Of the more than 95,000 women, over 41,000 also recalled their diet during their teenage years.
Over the 24-year study, 109 of the nurses developed bowel cancer before turning 50.
Every additional sugary drink was linked to a 16% higher risk, rising to 32% when the beverage was consumed during their adolescence.
When it comes to adult consumption, substituting a sugary soda for an artificially-sweetened alternative, coffee, or semi-skimmed or whole milk reduced the risk by 17% to 36%, the results suggest.
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The findings remained the same after the scientists adjusted for other factors that may influence a person's bowel cancer risk, like a family history of the disease.
Other experts have pointed out, however, some risk factors are hard to account for, like an excessive red meat consumption.
As well as reducing feelings of fullness, sugary drinks may trigger a rapid rise in blood glucose levels and subsequent secretion of the blood-sugar-lowering hormone insulin.
Over time, this could lead to damaging inflammation and insulin resistance, when cells do not respond properly to the hormone.
The sugar fructose, present in many sodas, may also make the gut "leakier", which could then cause cancer.
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The scientists have stressed the study was observational, and therefore does not prove cause and effect.
It is unclear if the results apply to men. Most of the nurses were also white, with it being unknown if sugary sodas may pose the same risk to women of other ethnicities.
Some experts have also questioned the accuracy of the women recalling their soda consumption during their teenage years.
"Overall, these findings should be considered as preliminary and exploratory until larger studies are done in other populations," said Dr Carmen Piernas, from the University of Oxford.
"Meanwhile, there is already strong evidence consuming sugary drinks increases [the] risk of weight gain and diabetes.
"Everyone should aim to minimise their consumption. This analysis does not change that advice."
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