A spice used in curry dishes helps to prevent infection and now scientists think they've got a lead on how.

Curcumin is a compound found in turmeric, a flavourful, orange and yellow spice that is a key ingredient in South Asian and Middle Eastern cuisine. The spice has also been used in India's traditional Ayurvedic remedies for 2,500 years.

Curcumin is a compound found in turmeric, a flavourful, yellow spice common in Indian curries. (Alastair Grant/Associated Press)

Now American and Danish scientists have found curcumin increases levels of a protein called CAMP that helps the immune system to fight off bacteria, viruses and fungi the first time they try to attack.

CAMP is the only known antimicrobial of its type in humans, researchers say.

"This research points to a new avenue for regulating CAMP gene expression," said Adrian Gombart, an associate professor of biochemistry and biophysics at the Linus Pauling Institute in Corvallis, Ore.

"It's interesting and somewhat surprising that curcumin can do that, and could provide another tool to develop medical therapies," he added in a release.

In Friday's issue of the Journal of Nutritional Biochemistry, Gombart and his colleagues said curcumin caused levels of CAMP to almost triple in laboratory experiments on human cells.

Vitamin D also increases levels of CAMP but high amounts of the vitamin can lead to more calcium being released into the blood. That's one reason researchers are testing other natural alternatives like curcumin.

CAMP seems to kill a broad range of bacteria including those that cause tuberculosis and also seems to protect against the development of sepsis, a serious body-wide response to infection that patients often acquire while being treated in hospital.

Earlier this month, researchers in England announced the first human trials testing curcumin to fight cancer. They hope it will increase the effectiveness of chemotherapy while reducing side-effects.

"We've shown that [curcumin] has well over 100 mechanisms of damaging cancer cells, particularly colon cancer cells," Professor Will Stewart from England's University of Leicester told the Australian Broadcasting Corporation.

"One of the major mechanisms is affecting the way that they grow blood vessels into themselves."