What Are Cranberry and D-Mannose?

What cranberry is

Cranberry, botanically Vaccinium macrocarpon, is the bright red fruit of a low growing shrub native to North America that thrives in acidic, boggy soils. One frequent confusion is worth clearing up at the outset: cranberry is not the same plant as the cornelian cherry (Cornus mas), which grows in Anatolia and is often given a similar common name in Turkish. The true relatives of cranberry are blueberry and lingonberry, all members of the genus Vaccinium.

The taste of the fruit is markedly sour and astringent, so it is rarely eaten fresh. It reaches the consumer mostly as juice, dried fruit, concentrate, powder and standardised extract.

The way it is harvested explains the image most people recognise from photographs: at the end of ripening the fields are flooded, the berries rise to the surface thanks to the small air pockets inside them, and they are collected from the water. Most of the world crop is grown in the United States, Canada and Chile; it reaches Turkey mainly as dried fruit, concentrate or extract.

The most discussed group among its constituents is the proanthocyanidins (PACs). These are plant compounds built from linked flavonoid units; what distinguishes cranberry from other PAC sources such as grape seed is that a substantial share of the links in its chains are of the A type, that is, formed by a double bond between units. The fruit also contains the anthocyanins responsible for its red colour, flavonols such as quercetin, organic acids including benzoic, quinic, citric and malic acid, vitamin C and soluble fibre.

What D-mannose is

D-mannose is a six carbon simple sugar. Its formula is all but identical to that of glucose; the only difference is that the hydroxyl group on the second carbon atom points the other way. In chemistry this relationship is called epimerism. Mannose occurs naturally in small amounts in fruits such as apples, peaches, oranges, blueberries and cranberries, and is produced commercially by breaking down a plant sugar polymer called mannan.

Mannose is not foreign to the human body. It is a natural building block in the sugar chains of glycoproteins on the cell surface, and the body can make it from glucose. When taken by mouth, part of it is absorbed in the small intestine, and most of the absorbed fraction is excreted unchanged in the urine rather than being burned for energy. Its effect on blood sugar is limited compared with the same amount of glucose, though it is not absent.

These two properties, passing into the urine without being metabolised and keeping its sugar structure, explain why research on D-mannose concerns the urinary tract.

Topics studied in research

In the scientific literature these two constituents are studied mostly under the heading of bacterial attachment to surfaces. Some bacteria of intestinal origin carry thin hair like projections called fimbriae on their surface. The proteins at the tip of these projections recognise particular sugar structures on tissue surfaces in a lock and key fashion. The binding of the FimH protein at the tip of type 1 fimbriae to mannose containing structures is an example described in detail in structural biology work. What free mannose present in urine does during that recognition process is a question investigated in cell culture and animal models.

The A type proanthocyanidins of cranberry have been studied in the laboratory in relation to attachment associated with P type fimbriae. Changes measured in urine composition after consumption of the fruit, for instance levels of hippuric acid and phenolic metabolites, form a separate line of research. General information on the acidity of urine is given in the article on urine pH.

What laboratory findings mean in everyday life remains a research question. Results from studies in humans are not uniform; the proanthocyanidin content of the products used, the daily amount and the duration of use vary from study to study, which makes comparison difficult. Scientific bodies therefore still treat the area as one where research is ongoing, and it would not be correct to draw a firm conclusion from any single study.

Use in food and supplements

Cranberry is consumed as a food mostly in the form of juice. Pure juice is very sour, so most commercial products are sweetened with sugar or blended with other fruit juices; the proportion of juice stated on the label differs considerably between products. Dried fruit is usually prepared by steeping the berries in sugar syrup. In North American cooking the fruit also appears as a sauce served alongside meat dishes.

In the food supplement field, cranberry extract and D-mannose, alone or together, are ingredients widely used with the aim of supporting urinary tract health, and research on them continues. Reading the label matters with extracts: standardised products state the proanthocyanidin content in milligrams, while expressions such as "juice equivalent" do not on their own say enough about what is inside. D-mannose is usually supplied as a readily soluble powder or as tablets, and tastes mildly sweet.

As for storage, cranberry products should be kept away from light and moisture, and once the packaging is opened the conditions stated on the label should be followed. Since polyphenols can decline over time with heat and prolonged contact with air, it is sensible to close extract containers tightly and to keep an eye on the expiry date.

For health-related questions, consult your physician or pharmacist.

Points to keep in mind

Blood thinning medicines. Interactions with cranberry juice have been reported in people taking vitamin K antagonists such as warfarin. If you use these medicines, do not consume cranberry products regularly without consulting your physician or pharmacist.

Oxalate content. Cranberry is among the fruits that carry oxalate. People with a history of calcium oxalate stones would do well to discuss the amount they consume with their physician; the general framework of the subject is set out in the article on kidney stones.

Sugar load. Commercial juices and sweetened dried fruit may contain a considerable amount of added sugar, and D-mannose is itself a sugar. Anyone monitoring blood sugar should read the label and consult their pharmacist.

Digestive complaints. Bloating, gas and loose stools have been reported in some people when large amounts are taken.

Special situations. Use of supplements during pregnancy and breastfeeding, in children, and in people with impaired kidney function requires assessment by a physician.

Symptoms such as fever, flank pain, blood in the urine, nausea and vomiting, or persistent painful urination, call for prompt medical attention. This page is intended as general information; for diagnosis and treatment consult your physician, and for questions about medicines consult your pharmacist.

Frequently asked questions

Are cranberry and cornelian cherry the same fruit?

No. Cranberry (Vaccinium macrocarpon) is the fruit of a plant in the heath family and a relative of the blueberry. The cornelian cherry that grows in Anatolia is Cornus mas, an entirely different species. The similarity of their common names in Turkish causes frequent confusion.

Is D-mannose a sugar, and does it raise blood sugar?

D-mannose is a six carbon simple sugar and an epimer of glucose. Because most of the absorbed fraction is excreted unchanged in the urine, its effect on blood sugar is limited compared with the same amount of glucose, though it is not absent. Anyone monitoring blood sugar would do well to consult their physician or pharmacist.

Should cranberry juice or extract be preferred?

The two are not equivalent in content. In commercial juices the share of juice and the amount of added sugar vary widely between products, whereas standardised extracts state the proanthocyanidin content in milligrams. For a product suited to you, you may consult your pharmacist.

Does cranberry interact with medicines?

Interactions with cranberry juice have been reported in people taking vitamin K antagonist blood thinners such as warfarin. If you take medicines regularly, consult your physician or pharmacist before starting any supplement.

Can people with a history of kidney stones consume cranberry?

Cranberry is among the fruits that carry oxalate, so people with a history of calcium oxalate stones are advised to discuss the amount they consume with their physician. General information on stone types and diet is given in our article on kidney stones.

What is a proanthocyanidin, and why is the A type emphasised?

Proanthocyanidins are plant compounds built from linked flavonoid units. In cranberry a substantial share of the links in the chains are formed by a double bond, which is called the A type. Laboratory work examines this bond type separately, which is why labels mention it.

Aymed İlaç Sanayi manufactures authorised medicinal products in urology and nephrology. This page does not contain diagnostic or treatment advice; it is intended as general health information.