What is Cranberry?
Cranberry is the small, sour red berry of Vaccinium macrocarpon, a low creeping shrub. It grows in bogs and marshes across North America, so it is also called marsh cranberry. The fruit and its juice are the parts used.
Most people take it to help prevent urinary tract infections (UTIs, bladder infections). American folk healers and Eclectic doctors used it for bladder and kidney complaints. It is also an everyday food: juice, sauce and dried berries.
Here is the honest verdict. Good trials show cranberry products can lower the chance of a repeat UTI in some people. Women who get infections often are the clearest group.
Cranberry does not treat an infection you already have. And long traditional use is not proof that a remedy works, or that it is safe.
How does Cranberry work?
The leading idea is that cranberry makes it harder for germs to stick to the bladder wall. Cranberry holds compounds called A-type proanthocyanidins. In lab studies, these appear to block common gut bacteria from gripping the cells that line the urinary tract.
Germs that cannot stick are washed out more easily in urine. But that is lab and urine-sample work. It is not proof of what happens inside your body.
An older idea was that cranberry acidifies the urine (makes it more acid). The acid was thought to kill germs that way. Normal amounts do not change urine acidity much, so most researchers have set that theory aside.
In test tubes, cranberry extracts also appear to slow biofilms. These are the slime layers that bacteria build. Whether that matters in people is not known.
What forms does Cranberry come in?
Cranberry is sold both as a food and as a supplement. The main food forms are juice, juice cocktail, sauce and sweetened dried berries. Fresh and frozen whole berries show up mostly in autumn.
Supplement forms are capsules, tablets, soft gels and powders. These hold dried juice or whole-fruit extract. Some are many times stronger than juice by weight.
Strength varies a lot between brands. Trials that found a benefit often used products giving about 36 mg of PACs a day. Many shop products do not state their PAC content at all.
Juice cocktail is often mostly water and sugar. Unsweetened juice is very sour and is usually watered down. Check the label for the share of real cranberry juice.
Where it comes from:
Native peoples of eastern North America ate cranberries, mixed them into pemmican, and used them on wounds. Early colonists took up the berry as a food and as a ship's store against scurvy.
Nineteenth-century American folk practice and Eclectic doctors gave cranberry for bladder and kidney complaints. Mashed berries were also used as poultices on the skin.
The idea that cranberry juice keeps bladder infections away became common household advice in the twentieth century. Researchers only began testing it carefully in the 1990s.
Who should avoid Cranberry?
- Do not use cranberry instead of antibiotics for a urinary infection you already have.
- Do not start cranberry supplements if you take warfarin, unless your doctor agrees and checks your INR (a blood clotting test).
- Avoid strong cranberry tablets if you have had calcium oxalate kidney stones, unless your doctor approves.
- Do not take cranberry supplements in pregnancy or while breastfeeding without asking your doctor; only food amounts are well studied.
- Never give cranberry supplements to a child without a doctor's advice.
- Do not use cranberry in any form if you are allergic to cranberry or to related berries such as blueberry or bilberry.
- Avoid sweetened cranberry juice if you have diabetes and your blood sugar is not well controlled.
- Avoid large daily amounts of the juice if you have reflux (acid coming back up) or a peptic ulcer (a sore in the stomach lining) and it makes you worse.
When should you see a doctor?
See a doctor if you have burning when you pass urine for more than a day or two.
Get urgent care for fever, chills, back or side pain, vomiting, or blood in your urine. These can mean the infection has reached a kidney.
Stop cranberry and get emergency help for a rash, swelling of the lips, mouth or face, or trouble breathing.
If you take warfarin, tell your doctor about any unusual bruising, nosebleeds or bleeding gums.
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