Blueberries are flowering plants of the genus Vaccinium with dark-blue, -purple or black berries. Species in the section Cyanococcus are the most common fruits sold as "blueberries" and are mainly native to North America. They are usually erect but sometimes prostrate shrubs varying in size from 10 cm tall to 4 m tall. In commercial blueberry production, smaller species are known as "lowbush blueberries" (synonymous with "wild"), and the larger species as "highbush blueberries". The leaves can be either deciduous or evergreen, ovate to lanceolate, and from 1–8 cm long and 0.5–3.5 cm broad. The flowers are bell-shaped, white, pale pink or red, sometimes tinged greenish.
The fruit is a false berry 5–16 mm diameter with a flared crown at the end; they are pale greenish at first, then reddish-purple, and finally blue on ripening. They have a sweet taste when mature, with variable acidity. Blueberry bushes typically bear fruit from May through June though fruiting times are affected by local conditions such as altitude and latitude.
Blueberries are sold fresh or processed as individually quick frozen (IQF) fruit, purée, juice, or dried or infused berries which in turn may be used in a variety of consumer goods such as jellies, jams, pies, muffins, snack foods, and cereals.
Blueberry jam is made from blueberries, sugar, water, and fruit pectin. Premium blueberry jam, usually made from wild blueberries, is common in Maine, Ontario, Quebec, and British Columbia.
Blueberries have a diverse range of micronutrients, with notably high levels (relative to respective Dietary Reference Intakes) of the essential dietary mineral manganese, vitamin B6, vitamin C, vitamin K and dietary fiber (table). One serving provides a relatively low glycemic load score of 4 out of 100 per day.
Especially in wild species, blueberries contain anthocyanins, other antioxidant pigments and various phytochemicals possibly having a role in reducing risks of some diseases, including inflammation and certain cancers.
Researchers have shown that blueberry anthocyanins, proanthocyanidins, resveratrol, flavonols, and tannins inhibit mechanisms of cancer cell development and inflammation in vitro. Similar to red grape, some blueberry species contain in their skins significant levels of resveratrol, a phytochemical.
Although most studies below were conducted using the highbush cultivar of blueberries (V. corymbosum), content of polyphenol antioxidants and anthocyanins in lowbush (wild) blueberries (V. angustifolium) exceeds values found in highbush species.
At a 2007 symposium on berry health benefits were reports showing consumption of blueberries (and similar berry fruits including cranberries) may alleviate the cognitive decline occurring in Alzheimer's disease and other conditions of aging.
Feeding blueberries to animals lowers brain damage in experimental stroke. Research at Rutgers has also shown that blueberries may help prevent urinary tract infections.
Other animal studies found that blueberry consumption lowered cholesterol and total blood lipid levels, possibly affecting symptoms of heart disease. Additional research showed that blueberry consumption in rats altered glycosaminoglycans which are vascular cell components affecting control of blood pressure.