Consumer awareness of the health benefits of garlic, mostly in terms of cardiovascular and immune system health, has benefited the supplements industry, particularly since consumers seek the benefits of garlic without the odours that accompany the fresh bulb.
Garlic supplements are worth more than $100m (€79.5m) in the US and are also one of the biggest sellers in the UK market. According to a 1998 survey by Hartman and New Hope, garlic supplements are used twice as much as other herbal supplements.
Several compounds from garlic have already been reported to have anti-cancer activity, including allicin, the substance that gives garlic its distinctive aroma and flavour, and its derivative, diallyl disulfide (DADS). However, both have been shown to kill not only cancer cells, but also healthy human body cells. The compounds are highly unstable and break down quickly once ingested, and are not likely to be the active compounds in ingested garlic.
"Water-soluble compounds, less odorous than the oil-soluble compounds, besides being more stable, appear to have a higher bioavailability and appear to be able to enter the blood and reach target organs," explained lead author Angelo De Martino in the Journal of Nutrition Biochemistry (doi: 10.1016/j.jnutbio.2005.12.005).
The researchers, from the University of Rome, obtained extracts from fresh garlic bulbs from two different geographical locations, and added these extracts to human liver cancer cells. The potential inhibition of the cancer cells was compared with a control batch of cancer cells (no intervention) and cancer cells exposed to DADS.
After 48 hours the researchers found that the control liver cancer cells had multiplied by over 300 per cent. Similar results were observed for the DADS-exposed cancer cells. A one per cent solution of each garlic extracts appeared to inhibit the growth of the tumour completely.
The garlic extracts, said the researchers, "showed a dose- and time-dependent effect on cell proliferation, with a significant reduction of viable cell number at 24 hours with a less pronounced recovery of cell proliferation at 48 hours."The researchers admitted that they had not identified the specific compound or compounds responsible for the anti-cancer effects of the water-soluble garlic extracts, nor could they be sure if the compounds were modified during their metabolic processing.
"Metabolomic studies should be performed in the future to investigate which are the molecules… that promote cell death upon administration of water-soluble garlic extracts," suggested De Martino.
Importantly, the researchers reported that the induction of apoptosis (programmed cell death) by the garlic extracts appeared to be selective to cancer cells.
De Martino said that, since the liver is where nutraceuticals are metabolised and that the cancer cells used in this experiment are known to be resistant to several anticancer therapies, that the results suggest the water-soluble garlic extracts may be effective against other forms of cancer.
It should be stressed that inhibition of cancer cell growth in a laboratory experiment may not be transferable to actual inhibition in humans. This study does however add to other research reporting that garlic and its extracts may protect against certain types of cancer.
Liver cancer is the sixth most commonly diagnosed cancer in the world, and third most common cause of death from cancer, according to Cancer Research UK. Despite these figures, the cancer remains relatively rare, with 18,500 new cases in the US every year, and about 3,000 in the UK.
The highest incidences of the disease are in east and Southeast Asia, and middle and eastern Africa. South Central Asia and Northern Europe have the lowest incidence of the disease.