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| The study looked at a particular substance, not human diet |
The Daily Express has reported that a luteolin-rich diet prevents cancer, but this research was carried out in cells in the laboratory, and did not test the effect of the compound in humans. Also, the luteolin used in this research was in a highly concentrated pure dose, and not from dietary sources. The study demonstrates how pure luteolin reduces the growth of bowel cancer cells in the laboratory, but does not show that a diet high in luteolin-containing vegetables can prevent cancer.
However, there is a great deal of existing research supporting a link between fruit and vegetables and benefits such as a reduced risk of bowel cancer. On this basis, there is already enough evidence to recommend including fruit and vegetables as part of a balanced diet.
Where did the story come from?
The study was carried out by researchers from Hallym University and other institutions throughout Korea. The research was funded by the Korean Ministry of Education, Science and Technology.
The study was published in the peer-reviewed open-access medical journal BMC Gastroenterology.
By itself, this study is not enough to support headlines claiming that a diet high in fruit and vegetables can prevent bowel cancer. Rather than examining the health effects of eating luteolin-containing foods it tested a dose of pure luteolin on bowel cancer cells grown in a laboratory. It is premature to link these laboratory-based results to dietary intake of luteolin.
What kind of research was this?
This was a laboratory study that examined the effect of a common plant compound called luteolin on bowel cancer cells. Luteolin is a type of plant pigment called a ‘flavonoid’, and it has antioxidant and suspected anti-cancer properties.
The researchers performing this study had previously shown that luteolin can stop bowel cancer cells in the laboratory from dividing, and can cause them to die. They thought that luteolin may do this by interfering with a particular biochemical chain of events called the ‘IGF-IR pathway’, which is known to be overactive in bowel cancer cells. This pathway causes cancerous cells to grow and divide, and prevents them from dying off naturally as healthy cells do.
This research was conducted in a laboratory setting, and did not involve any human participants. Its aim was to identify the effects of luteolin on bowel cancer cells, as a very early step in determining whether this chemical or a similar one might be used as a cancer treatment. It did not assess the potential cancer-preventing effects of eating luteolin-containing vegetables and herbs.
What did the research involve?
The researchers first grew human colon cancer cells in the laboratory, starved them for one day, and then divided them into four groups:
- group 1 was exposed to luteolin but no insulin-like growth factor I (IFG-I), which is known to activate the IGF-IR pathway under study
- group 2 was exposed to luteolin and IGF-I
- group 3 was exposed to IGF-I, but no luteolin
- group 4 was exposed to neither luteolin nor IGF-I
The researchers then measured and compared the number of cancer cells present after one, two and three days, across all the exposure groups. The researchers compared the average number of cells, and determined whether or not there was a statistically significant difference in the number of cells present in each group.
The researchers also carried out a variety of experiments to determine what components of the IGF-IR pathway luteolin interferes with.
What were the basic results?
When assessing the effect of luteolin on the growth of bowel cancer cells, the researchers found that the cells exposed to only IGF-I significantly increased in number, while those exposed to only luteolin significantly reduced in number. The group exposed to both luteolin and IGF-I showed the same reduction in the number of cells as the luteolin-only group, implying that luteolin interferes with the effect of IGF-I.
They also found that luteolin reduces the secretion of a protein called IGF-II by the cancer cells, reduces the amount of a key protein in the signalling pathway and interferes with several chemical processes in the signalling pathway. All of these actions reduce the activity of the cancer-related IGF-IR signalling pathway.
How did the researchers interpret the results?
The researchers say that luteolin reduced the activity of a key signalling pathway that is overactive in bowel cancer cells, and that this may account for the reduction of cell growth and increase in natural cell death seen in these cells when exposed to luteolin. They say that further animal studies are necessary to determine whether or not luteolin can be developed into an effective therapy for bowel cancer.
Conclusion
This research studied luteolin, which is a plant compound that can reduce growth and induce death of bowel cancer cells in the laboratory. The research seems to have pinpointed the specific signalling pathway through which this occurs. It did not, however, examine the impact of luteolin-rich diets on bowel cancer in people, and based on these results it cannot be assumed that eating vegetables containing this compound can prevent or slow cancer.
Laboratory-based studies carried out in cells are a necessary first step in identifying a potential new disease treatment. The mechanism through which luteolin may prevent cancer cell growth has been identified, and the next step would be further studies in animals. If these animal studies suggest that luteolin is safe and beneficial, limited trials in humans would then be needed to assess its effect on human disease. In short, this study represents an extremely early stage of research, and it will be several years before its results could result in any new treatments in humans.
It is important to remember that this study used pure luteolin, and not dietary sources of the compound. The effect of dietary luteolin on cancer is not clear from this research.
Systematic reviews of observational studies have found a link between eating a diet high in plant foods and a reduced risk of bowel cancer. Therefore, despite the limitations of the current study, a diet high in fruit and vegetables is certainly a healthy choice, and is recommended by schemes such as 5 A DAY.
Links to the headlines
How a diet packed with fruit and veg can ward off cancer. Daily Express, January 23 2012Links to the science
Young Lim D, Jin Cho H, Kim J et al. Luteolin decreases IGF-II production and downregulates insulin-like growth factor-I receptor signaling in HT-29 human colon cancer cells. BMC Gastroenterology 2012, 12:9http://www.nhs.uk/news/2012/01January/Pages/luteolin-flavonoid-cancer-prevention.aspx
