- Ian Sample, science correspondent
- The
Guardian
- Monday August 20 2007
Natural pigments that give
certain fruit and vegetables a rich red, purple or blue colour
act as powerful anti-cancer agents, according to a study by American
scientists.
The compounds, found in foods
such as aubergines, red cabbage, elderberries and
bilberries, restricted the growth of cancer cells and in some cases killed them
off entirely, leaving healthy cells unharmed.
The study combined laboratory
tests on human cancer cells with experiments on animals that were designed to
see whether a diet rich in the foods made a difference to their risk of
developing cancer.
Foods with the highest levels of the compounds were most effective at
slowing cancer growth, with exotic purple corn and chokeberries stopping the growth of colon cancer cells and killing 20%
in lab tests. Foods less enriched with the pigments, such as radishes
and black carrots, slowed the growth of colon cancer cells by 50% to 80%.
The findings bring scientists
closer to unravelling the key ingredients responsible
for giving fruit and vegetables their cancer-fighting properties.
Because the pigments, which
belong to a class of antioxidant compounds known as anthocyanins,
are not easily absorbed by the bloodstream, they travel through the stomach to the
gastrointestinal tract, where they are taken up by surrounding tissues.
Their survival through to the
lower part of the intestine may be the key to their role in preventing cancers
in the tract, the scientists believe.
Researchers led by Monica Giusti, an expert in plant nutrients at
When the team calculated how much of each extract was needed to reduce
cancer cell growth by 50%, they found anthocyanin
from purple corn to be the most potent. Chokeberries and bilberries were
nearly as effective, while radish anthocyanin
required nine times as much - or 131 micrograms per millilitre
of cancer cell solution to cut cell growth by half.
In a second study, the
researchers fed rats with colon cancer a diet of anthocyanin
extracts from bilberries and chokeberries, which are most often used as flavourings in jams and fruit drinks.
"These foods contain many
compounds and we're just starting to figure out what they are and which ones provide
the best health effects," said Dr Giusti.
"All fruits and vegetables
that are rich in anthocyanins have compounds that can
slow down the growth of colon cancer cells, whether in experiments in
laboratory dishes or inside the body."
The research was presented
yesterday at the annual meeting of the American Chemical Society in
The team are
now investigating whether it is possible to modify the structure of the pigment
compounds to make them even more potent. Tentative results so far suggest that
grafting an extra sugar or acid molecule to the anthocyanins
improved their effectiveness.
The work is part of a long-term
investigation aimed at a greater understanding of the 600 anthocyanins
found in nature. "We're just beginning to scratch the surface of
understanding how the body absorbs and uses these different structures,"
Dr Giusti said.
In June, market researchers
reported that sales of anthocyanin-rich blueberries
had doubled in the past two years. The berries joined a growing list of what
associations marketing the products call "superfoods",
alongside oily fish, brazil nuts and tomatoes. Anthocyanins have previously been linked to
helping towards a healthy heart and with treating skin conditions.