Myths and history · 4 min read

Why is urine sweet in diabetes?

Doctors noticed sweet urine for centuries before anyone could explain it. The answer is in your kidneys, and it also explains why a urine test was never enough.

Published 23 Oct 2026Sources checked 22 Oct 2026

In this article
  1. Why urine turns sweet
  2. Who noticed first
  3. Where "diabetes mellitus" comes from
  4. What a urine test can show
  5. Is sweet urine always diabetes?
  6. Questions
  7. Sources

The short version

  • Your kidneys normally take back almost all the sugar they filter. Above about 10 mmol/L (180 mg/dL) of blood sugar, they can't keep up, and the extra spills into urine.
  • Doctors noticed the sweetness long before they understood it. The word mellitus means honey-sweet.
  • A urine test only sees sugar above that threshold, hours late, and can never show a low. That is why diabetes is confirmed with a blood test, not a urine test.

Why does urine turn sweet?

In someone without diabetes, the kidneys filter about 180 grams of glucose out of the blood every day. Almost all of it is taken straight back in, mainly by a transporter called SGLT2, so almost none reaches the bladder.

That system has a limit. When blood sugar rises above about 10 mmol/L, the kidneys can't reclaim it fast enough, and glucose starts to appear in urine. Doctors call this glycosuria.

The kidney threshold for glucose A scale of blood sugar from 0 to 20 mmol/L. A typical range without diabetes, about 4 to 7, is shaded. At about 10 mmol/L a line marks the kidney threshold. Below it the kidneys reclaim the sugar. Above it, sugar spills into urine. About 10 mmol/L (180 mg/dL) Kidneys take it back Sugar spills into urine 0 4 7 10 15 20 mmol/L Typical without diabetes The kidney threshold for glucose About 10 mmol/L (180 mg/dL) Taken back Spills into urine 0 4 7 10 20 Typical without diabetes
The threshold is a gentle slope, not a hard line. It is lower in pregnancy and varies with age and kidney health.

Sugar in urine also pulls water with it. So you pee more, and then you feel thirsty. Those are two of the classic signs of diabetes the NHS lists, along with tiredness and losing weight without trying.

Who noticed it first?

The sweetness was spotted long before the science. A few of the people who wrote it down:

  1. AncientIndia: "honey urine"Ancient Indian medical texts called the condition madhumeha, honey urine. Later accounts say ants were drawn to it.
  2. 100sCappadocia: "diabetes"The Greek physician Aretaeus of Cappadocia used the word diabetes, from the Greek for passing through, because fluid seemed to run straight through the body.
  3. 1670sOxford: "wonderfully sweet"Thomas Willis wrote that his patients' urine was sweet, as if mixed with honey or sugar. He could not say why.
  4. 1776Liverpool: the sugar itselfMatthew Dobson boiled a patient's urine dry and was left with a powder that tasted like brown sugar. Their blood tasted sweetish too, the first hint that the sugar came from the blood.
  5. 1815Paris: grape sugarMichel Chevreul showed it was the same sugar found in grapes, which we now call glucose.
Some popular claims, such as an Egyptian papyrus describing diabetes, are debated by historians, so we've left them out.

Where does "diabetes mellitus" come from?

The full name, diabetes mellitus, is two words with two meanings. Diabetes is Greek for passing through, and describes the large amounts of urine. Mellitus is Latin for honey-sweet, and describes how that urine tasted. Put together, the name means sweet urine, and lots of it. Who first joined the two words is still argued over.

It was named to tell it apart from diabetes insipidus, where the urine is plentiful but tasteless. That is a different condition, caused by a problem with the hormone vasopressin rather than with sugar. In 2022 an international group proposed renaming it arginine vasopressin deficiency, partly to end the confusion.

What can a urine test show?

For blood sugar, a urine test can only answer one narrow question: did your blood sugar go above about 10 mmol/L at some point in the last few hours?

What a urine test can and can't see An illustrative day of glucose. It dips to 3.2 mmol/L at 3am and peaks at 13 mmol/L after lunch. Only the parts above the 10 mmol/L line would show up in urine. The night-time low would not show at all. Urine shows this 3.2 low at 3am: urine can't show it 10 4 00:00 06:00 12:00 18:00 24:00 What a urine test can and can't see Urine shows this 3.2 low at 3am: urine can't show it 10 4 00:00 12:00 24:00
An illustrative day, not a real person's data. Glucose in mmol/L.
  • It misses most of the picture. Anything under the threshold reads the same, whether you are at 5 or at 9.
  • It can't show a low. A hypo, the moment that matters most, is invisible.
  • It is hours old. Urine collects over time, so it tells you about the past.
  • It varies. The threshold differs between people, and how much you drink changes the result.

Urine tests are still useful for other things in diabetes care:

  • Ketones. High ketones can be a warning sign of diabetic ketoacidosis (DKA).
  • Kidney health. A urine test for a protein called albumin is part of regular diabetes check-ups.

What urine can't show is your average blood sugar. That is HbA1c, a blood test covering the last 2 to 3 months.

A finger-prick gives you the number right now. A continuous glucose monitor (CGM), such as a FreeStyle Libre or Dexcom, gives you the whole line.

Is sweet urine always a sign of diabetes?

No. Glucose can appear in urine with normal blood sugar too, for example in pregnancy, or in people whose kidneys have a naturally low threshold.

Some type 2 diabetes medicines do it on purpose. SGLT2 inhibitors, such as dapagliflozin and empagliflozin, block the kidneys from taking glucose back, so it leaves in urine. In one study, empagliflozin lowered the threshold to below 2.2 mmol/L (40 mg/dL). On these medicines, a urine test will show sugar whatever your blood sugar is.

If you're worried. The NHS lists peeing more than usual, feeling very thirsty, feeling very tired and losing weight without trying as signs of diabetes. See a GP, who can check with a blood test. If those symptoms get worse quickly, or come with being sick, stomach pain, fast deep breathing or confusion, call 999 or go to A&E.

Questions

Does sugary urine mean I have diabetes?

Not on its own. It can also happen in pregnancy, with a low kidney threshold, or on SGLT2 inhibitor medicines. If you have symptoms, a GP can check with a blood test.

At what blood sugar does glucose appear in urine?

For most people, above about 10 mmol/L (180 mg/dL). It is a gradual threshold, and it varies with age, pregnancy and kidney health.

What does diabetes mellitus mean?

Diabetes comes from the Greek for passing through, for the large amounts of urine. Mellitus comes from the Latin for honey, because the urine was sweet.

What can a urine test show in diabetes?

Sugar above about 10 mmol/L, ketones (a warning sign of DKA) and albumin (a kidney check). It cannot show a low, or your average blood sugar. That is HbA1c, a blood test.

Is diabetes insipidus the same as diabetes?

No. It is a separate condition caused by a problem with the hormone vasopressin, not with sugar. It causes large amounts of dilute urine and thirst.

Sources

  1. Karamanou M et al. Milestones in the history of diabetes mellitus: the main contributors. World Journal of Diabetes, 2016. PMC4707300
  2. Clarke SF, Foster JR. A history of blood glucose meters and their role in self-monitoring of diabetes mellitus. British Journal of Biomedical Science, 2012. Full text
  3. Science History Institute. Sickening sweet. Distillations. sciencehistory.org
  4. Royal College of Physicians of Edinburgh. Diabetes in the College collections. rcpe.ac.uk
  5. Ferrannini E. Learning from glycosuria. Diabetes, 2011. PMC3046828
  6. Al-Jobori H et al. Empagliflozin and kinetics of renal glucose transport. Diabetes, 2017. PMC7301160
  7. StatPearls. Glycosuria. NCBI Bookshelf
  8. Working Group for Renaming Diabetes Insipidus. Changing the name of diabetes insipidus: a position statement, 2022. PMC9578068
  9. NHS. Diabetic ketoacidosis. nhs.uk · Chronic kidney disease: diagnosis. nhs.uk
  10. Diabetes UK. What is HbA1c? diabetes.org.uk
  11. NHS. Type 1 diabetes: symptoms. nhs.uk · Type 2 diabetes: symptoms. nhs.uk · Diabetes insipidus. nhs.uk

Written by the glyso teamEvery article is checked against the sources listed above.

This article is general information, not medical advice. Always follow the guidance of your diabetes care team.