Does eating a lot of sugar increase my risk of cancer?
Drinking large amounts of sugar-sweetened beverages is associated with a noticeably higher risk of certain cancers, particularly early-onset colorectal cancer and liver cancer. The association is observational, but consistent enough to make reducing soft drinks and fruit juice a concrete point of attention.
Sugar-sweetened beverages have been studied most concretely. Women who drank two or more sugar-sweetened beverages per day had more than twice the risk of colorectal cancer before the age of fifty compared with women who drank fewer than one per week. Each additional serving per day was linked to a 16% higher risk. This comes from a cohort study1. Beverages consumed during the teenage years also showed an association: a 32% higher risk per additional serving per day, although the confidence interval just touches the boundary of statistical significance.
In postmenopausal women, drinking sugar-sweetened beverages daily was linked to nearly twice the risk of liver cancer, and to a 68% higher risk of dying from chronic liver disease. That is a substantial difference. Beverages containing artificial sweeteners showed no elevated risk in the same study.
A large Japanese cohort study found no clear association between total sugar intake and colorectal cancer overall. Only for rectal cancer in women was there a suggestion of a link at high sugar intake, and that picture was not consistent.
Laboratory and animal research offers clues about how sugar may influence cancer. In laboratory studies, the combination of glucose and fructose found in soft drinks makes colorectal cancer cells more mobile and promotes metastasis. Animal experiments show that fructose can accelerate tumour growth in melanoma and breast cancer, among others, via a detour through the liver: the liver converts fructose into certain fats that tumour cells use as building blocks. These are biological mechanisms, not yet direct evidence from studies in humans.
A broad review study concludes that regularly drinking sugar-sweetened beverages is associated with weight gain, type 2 diabetes, and an increased risk of certain cancers. Excess weight and insulin resistance are well-known intermediate steps that raise cancer risk. Estimates of how many cancers could be prevented through healthier eating vary widely and are surrounded by considerable uncertainty. The most concrete takeaway remains: limit sugar-sweetened beverages, because that is where the strongest evidence for a link with cancer lies.
All claims are based on observational (cohort) research in humans, supplemented by laboratory and animal research. No randomised trials are available for cancer outcomes. Causality has not been proven. PMIDs: 33958435, 36851860, 37552302, 40973819, 39633044, 35064240.
Does being overweight increase my risk of cancer, and if so, which types?
Excess weight increases your risk of at least 13 types of cancer, including uterine, colorectal, breast and liver cancer. Losing weight reduces that risk, although it remains unclear whether all methods of weight loss are equally effective for immune defence against cancer.
Does having type 2 diabetes increase your risk of certain cancers?
Type 2 diabetes increases the risk of several cancers, including liver, pancreatic, uterine and colorectal cancer. If you have diabetes, it is worthwhile to discuss with your doctor whether closer attention to early detection or lifestyle improvement is appropriate for you.
Does eating heavily heated or charred food increase your risk of cancer?
Heavily heated or charred meat likely increases the risk of certain types of cancer, although the associations in humans are associative. By not charring meat and varying cooking methods, you can substantially reduce your exposure to these substances.
Does sitting a lot increase my risk of cancer, even if I exercise?
Sitting a lot increases your risk of certain cancers, even if you exercise. In addition to moving regularly, try to reduce your sitting time itself, because the two only partially compensate for each other.
Does poor sleep increase my risk of cancer?
Poor sleep, and certainly untreated sleep apnoea, is associated with an increased cancer risk, but it has not yet been proven that sleeping poorly causes cancer. Have sleep apnoea checked if you have symptoms, and try to maintain a regular sleep schedule.
Does a large belly increase my risk of cancer more than being simply overweight?
A large belly increases the risk of several cancer types more than being simply overweight, especially in men. Having your waist circumference measured is therefore more meaningful than paying attention only to the scales.