Numerous studies have been done on the benefits of turmeric, a dark yellow spice commonly used in Indian and other Asian cuisines.

They have suggested that turmeric has anti-inflammatory properties. The spice is also reportedly helpful in preventing cancer or Alzheimer's disease, and treating inflammatory bowel diseases or indigestion.

The key ingredient in turmeric is curcumin. It is what gives the pungent spice its characteristic hue and it makes up about 2 to 3 per cent of turmeric.

Trials on rats have shown that unrealistically high doses of curcumin may inhibit the development of some types of cancer.

A BBC programme, Trust Me, I'm A Doctor, did an experiment to see if turmeric could boost one's health. It reported two months ago that cooking with turmeric might reduce the risk of cancer, though more research is needed.

For the experment, it divided about 100 volunteers into three groups.

One group consumed a teaspoon of tumeric, ideally mixed with their food, every day for six weeks. Another group swallowed a supplement containing the same amount of turmeric and a third group was given a placebo, or a dummy pill.

The programme asked Professor Martin Widschwendter and his team from University College, London, to test the DNA methylation patterns, or chemical modifications to the DNA of the volunteers' blood cells at the start and end of the experiment.

It was to see if the changes in the DNA might indicate that the volunteers' bodies were switching on and off different genes that might be related to diseases.

The supplement group and the placebo group showed no changes.

However, significant changes were found in those who added turmeric powder to their food.

The biggest change involved a gene known to be associated with the risk of cancer, as well as with allergies like asthma and eczema, and anxiety and depression.

The study suggested that simply adding a teaspoon of turmeric to your daily food or beverages like tea can make a change to your DNA, in a way that could well reduce your risk of cancer, allergies and possibly even depression.

It is possible that cooking can make curcumin more soluble.

Ms Jaclyn Reutens, a dietitian at Aptima Nutrition in Singapore, said the theory that heat and dissolving agents such as milk, water and oil increases the effectiveness of curcumin is highly plausible.

What was noteworthy was that turmeric in the form of a supplement had no effect. But turmeric that was eaten with food showed beneficial effects.

"This is what dietitians advocate, to consume nutrients as often as possible in the form of whole foods rather than in the form of a pill," said Ms Reutens.

However, it has not been proven conclusively that turmeric is effective in cancer prevention and treatment, said Ms Sarah Shamila, manager of Nutrition and Dietetics Services at Mount Alvernia Hospital.

Dr Wong Seng Weng, medical director and consultant medical oncologist at The Cancer Centre, said the use of turmeric in the treatment or prevention of cancer has not gained acceptance by mainstream scientific medicine because of the very limited and inconsistent scientific research on its benefits.

Most of the research has been done in laboratories and not on humans.

"Curcumin has many characteristics that may be barriers to translating the purported benefits seen in laboratory models to human subjects," said Dr Wong, who is also an adjunct clinician scientist at the Agency for Science, Technology & Research.

"Curcumin is poorly absorbed when ingested and rapidly cleared by the body's metabolism. It is probably extremely difficult to achieve the level needed to replicate the biologic effect seen in laboratory models within the human body."

Dr Wong said there is concern that it may affect the efficacy of common chemotherapy drugs such as cyclophosphamide, by interfering with the way these drugs are cleared by the human body. He would prefer that patients undergoing chemotherapy do not take turmeric or curcumin supplements.

He said: "The only herbal remedy that I sometimes suggest to patients is ginger tea, to reduce nausea associated with chemotherapy."

Ms Reutens said that if turmeric is found to be truly effective against cancer, diabetes or other diseases one day, it should still be eaten as part of a healthy balanced diet.

"There is no one food or chemical that can cure and prevent a host of diseases on its own," she added.