Diabetes mellitus is a chronic, progressive disease caused by a lack of, or problems with processing, the hormone insulin. The result is persistently high glucose (sugar) in the blood, causing symptoms including slow-healing wounds, exhaustion, and increased thirst.

Roughly one in 10 adults have diabetes globally. The condition is considered an epidemic by the World Health Organization, though a quarter of adults with diabetes don't know they have the disease (see stats here). 


The body breaks down the food we eat into usable molecules. One of these is glucose, the body's main source of energy. It can be used by the body immediately or stored in the liver and muscles as glycogen for later use.

Once glucose hits the bloodstream—for example, after meals—the pancreas is responsible for controlling the body’s blood sugar level, jumping into action if it is too low or too high.

If blood sugar is too low, a molecule called glucagon is released, signaling to the body to convert and release stored sugar. When blood sugar is too high, the pancreas releases insulin, telling the body to send glucose to cells to use or store.

If the pancreas doesn’t release enough insulin, or cells don’t respond to insulin properly, glucose levels remain persistently high. This may eventually lead to a variety of serious health concerns—hardened blood vessels, damaged organs, high blood pressure, blindness, kidney disease, heart attacks and strokes, and even death.


There are two primary types of diabetes: Type 1 and Type 2. Gestational diabetes occurs in 2% to 10% of pregnancies and typically manifests in mild symptoms (see overview), though they may get worse for the baby and mother if left untreated.

Type 1 diabetes—formerly known as juvenile-onset diabetes—is a partially inherited autoimmune condition in which the body’s immune system attacks insulin-producing cells in the pancreas, undermining and potentially halting all production of the hormone.

Its exact cause is unknown (watch overview). A number of heritable genetic risk factors have been implicated, but they appear to often be triggered by environmental factors. Roughly 5% to 10% of diabetics fall into this category.

Type 2 diabetes occurs when your cells don’t respond normally to insulin or the pancreas can’t keep up with the amount of insulin needed to lower blood sugar levels.

While some genetic factors exist, primary drivers include diet (sugary or high in carbohydrates), lack of exercise (which lowers blood sugar by burning energy), and obesity (which reduces the ability of insulin to reach cells).


First recognized in 1500 BCE, diabetes was a "uniformly fatal" condition for centuries until the discovery of insulin supplements in the 1920s. 

Modern treatments typically hinge on such supplements, often administered as injections, though people with Type 2 diabetes can sometimes manage their condition with medication (see timeline).

Researchers are also exploring other potential treatments for the manageable disease, including cell therapy, fecal transplants, artificial pancreas, and pancreas stem cell manipulation.

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Insulin is a hormone released by islets of beta cells in the pancreas in response to rising blood sugar levels. Blood sugar levels increase after a meal when the body starts the process of turning food into usable fuel—meaning sugars, proteins, and other nutrient building blocks—that are then absorbed into the bloodstream via the intestines. Once blood sugar levels hit a certain point, as determined by the pancreas, insulin is released, enabling the sugar in the blood to be absorbed into hungry cells and dropping overall blood sugar levels.

Photo of a person being loaded into an ambulance during a medical emergency.
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Type 2 diabetics in the US are at risk of dying from low blood sugar, an epidemic traced to a decades-old, multi-million-dollar drug industry campaign encouraging an average blood sugar level below 7%. At the time, research correlated such levels with reduced risk of eye, nerve, and kidney damage and increased hypoglycemia risk. The campaign—supported by the American Diabetes Association, whose treatment guidelines are considered a gold standard—led to increased prescription dosages to meet the new treatment goal pushed by corporations, some of which remain major ADA donors.

Photo of stacked cubes of non-artificial sugar.
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Non-nutritive sweeteners such as stevia, sucralose, and others are increasingly replacing sugar in foods ranging from bread to canned soup. Research has revealed such sugar alternatives detrimentally impact the composition of user gut microbiomes and worsen the body's ability to regulate blood sugar. These "high-intensity" sweeteners are hundreds of times sweeter than table sugar, and some escape being labeled as artificial due to their "natural," plant-based origins.

Science History Institute

Is sugar as bad as it sounds?

Photo of enslaved peoples forced to work on a sugar plantation.
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Millions of years ago, humanity's ancestors evolved to wring more calories from sugary fruits by storing excess sugar as fat, an adaption that's culminated in many peoples' palettes preferring calorie-rich sweets. Sugar consumption can cause obesity and insulin resistance, factors that can lead to the development of diabetes, and causes the body to release insulin, a hormone that can aggravate cancer. And it's contribution to societal ills doesn't stop there; As an industry, sugar has even contributed to slavery, colonialism, and Nazi death chambers.

Closeup photo of surgical tools in an operating theater.
Open link on features.propublica.org

Diabetes-related amputations in the US sunder the limbs of Black patients at triple the rates of other races. Each year, about 130,000 US diabetics undergo these surgeries (possibly the most preventable in the country), which often take place in low-income and uninsured neighborhoods. More than half of US diabetics who lose their lower limbs are not subject to pre-surgery angiograms, imaging that shows blood flow blockages to determine if (and where) amputation is necessary.

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Scientists studying the barely-there feeding frequency of the Gila monster, a venomous lizard native to Mexico and the Southwestern US, found that its saliva had a hormone that regulated blood sugar and appetite. Further research revealed that this hormone resembled a human one known as GLP-1, giving rise to a class of drugs known as glucagon-like peptide 1 agonists, a generation of weight loss medications that seek to replicate the lizard's hormone.

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