Digestive and oral health

Digestive and oral health covers the digestive tract from the mouth, where the teeth and gums begin digestion, through the stomach to the colon and rectum, where water is absorbed and the gut microbiome (the community of bacteria living in the bowel) ferments undigested food. Each part has a common chronic disease with effects beyond the organ itself. In the colon it is colorectal cancer, the second most common cause of cancer death in the United States, with 52,550 deaths projected for 2023 [1]. In the mouth it is periodontitis, a chronic gum infection whose severe form affects about 11.2% of the world's population [2].

Colon health describes the large bowel, colorectal cancer and the factors that shift its risk. Most colorectal cancers grow slowly from non-cancerous polyps, and removing these polyps at colonoscopy (a camera examination of the bowel) was associated with 53% fewer colorectal cancer deaths than expected over up to 23 years [3]. Diet is the other main influence: the highest fibre eaters had 15 to 30% lower rates of death and of several diseases, including colorectal cancer, across 185 prospective studies (studies that follow people forward in time) [4], while each 50 g of processed meat eaten daily raises colorectal cancer risk by about 18% [5]. Colorectal cancer has become more common in younger adults, with the share of US cases diagnosed before age 55 rising from 11% in 1995 to 20% in 2019 [1].

Helicobacter pylori describes the stomach bacterium that is the leading infectious cause of cancer. It was linked to about 760,000 new cancers worldwide in 2024, most of them stomach cancers [6]. Most carriers never develop cancer, and in randomised trials treating the infection with antibiotics lowered later stomach cancer by 36% [7].

Oral health describes gum disease, tooth decay and tooth loss, and their links with the rest of the body. Periodontal (gum) disease was associated with 24 to 34% higher risk of coronary heart disease (narrowing of the arteries that supply the heart) in pooled cohort studies (studies that follow groups of people over time) [8] and with 21% higher risk of dementia, although the dementia evidence is rated low quality and is partly explained by reverse causation, in which early illness leads to poorer oral care [9]. In a randomised trial (a study that assigns participants to groups by chance), intensive treatment of severe gum disease improved blood vessel function after six months [10]. Most evidence in both areas is observational, from tracking people rather than assigning them to a diet, habit or treatment, so how much of each link is cause and effect is uncertain.