The old instruction was practical rather than poetic. Look after your teeth and your feet, because both are easy to ignore until they fail, and both fail in ways that travel, or in the case of feet, don't travel. A sore foot changes how you walk, then how your knees and back wear. A diseased gumline does something quieter. It keeps a wound open in the mouth, and the rest of the body has to live with what leaks out of it.

Gum disease starts as gingivitis: plaque at the margin, red gums, blood on the brush. Leave it, and it becomes periodontitis. The gum pulls away, pockets form, bone that holds the teeth is eaten back, and teeth loosen. In the United States about 42 percent of adults over 30 have some periodontitis. The severe form is common enough, worldwide, to count in the hundreds of millions. It is not a niche dental problem. It is one of the most widespread chronic inflammations people carry without calling it an illness.

The new attention is on the kidney. A Hamburg study of 6,179 adults, published in the International Journal of Oral Science and written up this week by Joseph Mercola (link below), found severe gum disease tied to worse kidney filtration and more albumin in the urine, a marker that the kidney's filter is leaking. Severe periodontitis was present in 14 percent of people with normal kidney function and 36 percent of those with moderately reduced function. Blood markers of inflammation, CRP and interleukin-6, rose with both conditions, but CRP explained only about a third of the link with reduced filtration and about a tenth of the link with albumin in the urine. Inflammation is part of the bridge. It is not the whole bridge.

An earlier follow-up of African American adults in the Jackson Heart Study pointed the same way. Among people whose kidneys were still working at the start, severe periodontal disease was associated with a roughly fourfold higher rate of later chronic kidney disease, after adjustment for age, sex, diabetes, blood pressure, smoking and income. That figure needs a cool head. Only 21 people developed kidney disease during follow-up, so the estimate is unstable. It is a signal, not a measurement you can take to the bank.

The direction of travel is also not one-way. Reviews in Nature Reviews Nephrology and a 2023 umbrella review of the systematic evidence, describe a two-way relationship. Periodontitis can feed systemic inflammation. Chronic kidney disease can make the mouth worse, through immune changes, a drier mouth, and the same oxidative stress that damages small vessels. Smoking, diabetes, age and hardship raise the odds of both. Shared causes explain some of the overlap. They do not appear to explain all of it.

The mechanism on offer is plausible, and still short of proof. Ulcerated gum pockets are a broken surface. Bacteria and their products, including those of Porphyromonas gingivalis, enter the blood in small amounts every time the gum is disturbed. The immune response that follows is useful in the mouth and costly if it never switches off. Endothelial irritation, oxidative stress and a low-grade rise in inflammatory mediators are the proposed route to the kidney, and the same route is invoked for blood vessels, glucose control and the heart. A very large Korean study found people who developed gum disease had about a 4 percent higher risk of atrial fibrillation over 14 years. That is a small relative shift in a common disease, which can still mean a large number of cases. It is not a reason to treat a bleeding gum as a pending stroke.

The Alzheimer's claim needs the same restraint. P. gingivalis and its enzymes have been reported in brain tissue of people who died with the disease. Finding a bacterium at the scene is not the same as proving it started the fire. The kidney evidence is further along than that, and still mostly association. What is missing is a clear trial showing that treating the gums slows the loss of kidney function. Smaller studies suggest periodontal treatment can nudge inflammatory markers and some kidney measures.

Feet belong in the same sentence for a reason that is not mystical. Teeth and feet are the parts people postpone. Both are load-bearing. Both get infected in people whose circulation and immunity are already under strain, especially with diabetes. A neglected foot ulcer and a neglected periodontal pocket are different tissues running the same pattern: a chronic wound, bacteria, inflammation, and a body that pays interest on the debt. Podiatry caught on to this earlier than dentistry did in general medicine. Nephrologists are starting to catch up. Dental checks are still rare in kidney clinics, and kidney checks are rare in dental surgeries.

None of this requires a special theory of the mouth. Brush, clean between the teeth, stop smoking, get pockets treated before bone is gone. Oil pulling and a "biological" dentist are optional extras. The Hamburg authors' own conclusion is the modest one: severe gum disease tracks with early kidney damage, and someone should test whether treating it preserves function.

The saying survives because it was never really about teeth or feet. It was about the unglamorous maintenance that keeps small wounds from becoming systemic ones. The modern version is only more specific. A bleeding gum is a dental problem. It may also be an early note from the kidney.

https://takecontrol.substack.com/p/gum-disease-and-kidney-health