Eating fish may help prevent prostate cancer
MANCHESTER, UNITED KINGDOM. Men face a much more dangerous form of prostate cancer if tumor cells from the prostate gland metastasize and migrate and invade other parts of the body, such as bone marrow. New research suggests that oily fish may help prevent this process. It appears that omega-3 fats contained in oily fish can prevent the cancer spreading to bone marrow, a process which may be encouraged by the other major group of polyunsaturated fatty acids – omega-6 fats. Researchers at the Christie Hospital in Manchester found evidence for this effect in laboratory tests, where they showed that omega-3 fats can inhibit invasion by prostate cancer cells, potentially reducing the threat of metastasis. They also found that omega-6 fatty acids, found in vegetable oils, nuts and seeds, increased the risk of tumor cells spreading into bone marrow. This invasion was blocked by omega-3 fats, which are found in oily fish such as salmon, mackerel and tuna.
The researchers believe that cancerous tumors may use omega 6 fats as a high-energy food, enabling rapid growth. Omega-3 fats are known to interfere with the various functions of omega-6 fats, they explain, and this was confirmed by the current findings. This effectively removes the cancer's 'free lunch', a fact that may have clinical importance. Eating a diet with the right balance of omega-3 and omega-6 fats may well help to keep prostate cancer within the prostate gland where it may be monitored safely or more easily treated with surgery or radiotherapy, they conclude, adding that a healthy balance of these two types of fat would be about half as much omega-3 as omega-6.
Brown, M.D. et al. Promotion of prostatic metastatic migration towards human bone marrow stoma by Omega 6 and its inhibition by Omega 3 PUFAs. British Journal of Cancer, Vol. 94, March 27, 2006. pp. 842-53
Fish oils help prevent prostate cancer
BETHESDA, MARYLAND. Alpha-linolenic acid (ALA) is a major component of flax seed oil and has been
associated with significant cardiovascular benefits. Some studies, however, have shown that a high
intake of ALA is associated with an increased risk of prostate cancer. A prestigious team of researchers
from the National Cancer Institute, the Harvard Medical School, the Harvard School of Public Health, and
the Karolinska Institutet in Stockholm has just released the results of a study aimed at settling the
controversy as to whether or not ALA is detrimental when it comes to prostate cancer. The researchers
also determined the effect of other fatty acids, including fish oils, on prostate cancer risk.
The study involved 47,866 male American health professionals who were followed over a 14-year period
beginning in 1986. The participants completed detailed food frequency questionnaires in 1986, 1990 and
1994. By the year 2000, 2965 new cases of prostate cancer had been reported with 448 of these being
advanced (metastasized) or fatal. The overall incidence of new prostate cancer detected over the 14-
year period was 0.5% per year.
The researchers found no correlation between ALA intake and overall prostate cancer risk, but did
observe a strong association between a high ALA intake and the risk of advanced prostate cancer. Men
with a high ALA intake (greater than 0.58% of energy or about 1.3 grams/day) were twice as likely to
develop advanced prostate cancer as were men with a lower intake (less than 0.37% of energy or about
0.8 grams/day) even after adjusting for all other known variables that could affect the risk. The risk was
slightly higher for ALA from non-animal sources than for ALA from meat and dairy sources. There was a
trend for red meat, mayonnaise and salad dressings to be associated with a higher risk. The intake of
two other abundant fatty acids, linoleic acid and arachidonic acid, was not related to prostate cancer risk.
The team of researchers found a protective effect associated with a high intake of fish oils -
eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Men with a daily intake of more than
0.214% of daily energy (about 470 mg/day) were 11% less likely to develop prostate cancer than were
men with an intake less than 0.057% of energy (about 125 mg/day). The beneficial effect of EPA plus
DHA was particularly pronounced in regard to the incidence of advanced prostate cancer. Fish oil
supplements were slightly less effective than fish oils from fatty fish perhaps indicating that vitamin D and
vitamin A are necessary to obtain the maximum benefit.
Leitzmann, MF, et al. Dietary intake of n-3 and n-6 fatty acids and the risk of prostate cancer. American Journal of
Clinical Nutrition, Vol. 80, July 2004, pp. 204-16
Fats and breast cancer
MILAN, ITALY. The association between the intake of various fats and oils and the risk of breast cancer
has been the subject of several studies. There is still no real consensus as to which fats are beneficial
and which are not. The evidence for a protective role of eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA), the main components of fish oils, is probably the strongest.
Researchers at the Italian National Cancer Institute have just completed an investigation aimed at
clarifying the association between fat intake and breast cancer risk. A total of 4052 postmenopausal
women were followed for an average of 5.5 years. During this time 71 cases of invasive breast cancer
were diagnosed. The cancer patients were matched with 141 controls. All study participants had blood
samples drawn and red blood cell (erythrocyte) membranes were analyzed for their fatty acid content.
The researchers point out that erythrocyte membranes are good biomarkers for not only dietary fat intake,
but also for other dietary and hormonal factors.
Women with DHA concentrations in the highest tertile had less than half the risk of breast cancer than did
women in the lowest tertile. Polyunsaturated fatty acids overall were also protective with omega-3 acids
being somewhat more protective than omega-6 acids. Saturated fatty acid concentrations were not
significantly related to breast cancer risk. A higher concentration of monounsaturated fats, especially
oleic acid, was associated with a significantly increased risk. The researchers point out that most oleic
acid in mammalian tissue is derived from saturated stearic acid through a process involving the enzyme
delta 9-desaturase. Saturated fatty acids, cholesterol, carbohydrates, insulin, testosterone, and estrogen
all activate this enzyme whereas dietary polyunsaturated fatty acids and fasting deactivate it. The
researchers conclude that the delta 9-desaturase enzyme may be an important link between breast
cancer risk and dietary fat consumption and urge further research in the field.
Pala, Valeria, et al. Erythrocyte membrane fatty acids and subsequent breast cancer: a prospective
Italian study. Journal of the National Cancer Institute, Vol. 93, July 18, 2001, pp. 1088-95
Fish consumption helps prevent prostate cancer
STOCKHOLM, SWEDEN. Several studies have shown an inverse relationship between blood levels of
fish oils (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) and the risk of prostate cancer.
A study just completed by medical researchers at the Karolinska Institute confirms this association.
The Swedish study involved 3136 pairs of male twins born between 1886 and 1925. The participants
completed food frequency questionnaires in 1961 and 1967 and were then followed up for 30 years. By
December 31, 1997 the researchers had recorded 466 diagnoses of prostate cancer (340 fatal ones).
The average age of diagnosis was 76.7 years. After adjusting for other known risk factors the
researchers conclude that men who never eat fish have a two- to three-fold higher risk of prostate cancer
than do men who eat moderate to high amounts. The researchers emphasize that only fatty fish such as
salmon, herring and mackerel, which contain high amounts of omega-3 fatty acids (EPA and DHA), would
be expected to be beneficial.
Terry, Paul, et al. Fatty fish consumption and risk of prostate cancer. The Lancet, Vol. 357, June 2,
2001, pp. 1764-66 (research letter)
Fish oils help prevent prostate cancer
AUCKLAND, NEW ZEALAND. Medical researchers in New Zealand provide convincing evidence that an
increased consumption of fish oils helps reduce the risk of developing prostate cancer. Their study
involved 317 men who had been diagnosed with prostate cancer during 1996-97 and 480 age-matched
controls. Blood samples were obtained from all participants and the erythrocyte (red blood cell)
phosphatidylcholine fraction of the plasma was analyzed for EPA (eicosapentaenoic acid) and DHA
(docosahexaenoic acid), the two main components of fish oils.
Evaluation of the collected data showed a clear correlation between blood level of EPA and DHA and the
presence of prostate cancer. Study participants with levels in the highest quartile were found to have a
40 per cent lower incidence than participants with levels in the lowest quartile. This relationship held true
even when adjusted for age, height, use of NSAIDs (non-steroidal anti-inflammatory drugs), socio-
economic status, and estimated intake of lycopene and polyunsaturated fats.
The researchers also found that men with low socio-economic status, a low intake of lycopene, and non-
regular use of NSAIDs were more likely to develop prostate cancer. They did not, however, find any
correlation between self-reported intake of EPA and DHA indicating that food frequency questionnaires
are not an accurate method for estimating fish oil intake. The researchers speculate that fish oils may
prevent the progression of prostate cancer by inhibiting the biosynthesis of eicosanoids from arachidonic
acid.
Norrish, A.E., et al. Prostate cancer risk and consumption of fish oils: a dietary biomarker-based case-control study.
British Journal of Cancer, Vol. 81, No. 7, December 1999, pp. 1238-42
Breast cancer risk linked to fatty acid profile
CHAPEL HILL, NORTH CAROLINA. Breast cancer rates differ greatly between countries. They are 5
times higher in the United States than in Japan and twice as high in France as in neighbouring Spain.
Differences in overall fat consumption in these countries have been extensively studied, but no link to
breast cancer incidence has been detected so far. A large team of researchers from the Netherlands,
Ireland, Spain, Finland, Switzerland, Germany and the United States now report that, while overall fat
consumption may not be significant, the make-up of the fats could be. As part of the large EURAMIC
Study the researchers investigated the link between the content of polyunsaturated fats in adipose (fat)
tissue of postmenopausal women and breast cancer incidence. A total of 291 women with breast cancer
and 351 controls were included in the study which involved 5 European medical centers. The women all
had samples of adipose tissue taken (from the buttocks) and analyzed to determine the concentration of
the main polyunsaturated fatty acids: the omega-3 acids - alpha-linolenic acid (ALA), eicosapentaenoic
acid (EPA) and docosahexaenoic acid (DHA), and the omega-6 acids - linoleic acid (LA) and its
metabolite arachidonic acid (AA).
The study found no significant correlation between omega-3 fatty acid levels and breast cancer incidence,
but did find a trend to increasing incidence with increasing levels of omega-6 fatty acids in the adipose
tissue samples. The researchers also found a significant association between the ratio of EPA and DHA
to LA levels and breast cancer incidence in 4 out of 5 of the medical centers involved in the study.
Pooling all results showed that women with the highest ratio had a 35% lower breast cancer incidence
than women with the lowest ratio. In other words, women with a relatively high adipose tissue level of
EPA and DHA (the main components of fish oils) and a relatively low level of LA and its metabolites had a
lower breast cancer risk. The researchers note that LA (linoleic acid) is the precursor of certain
eicosanoids which may promote tumour growth. EPA and DHA inhibit the production of these harmful
compounds and may also, on their own, inhibit tumour growth. The researchers also point out that
several epidemiological studies have found an inverse correlation between fish consumption and breast
cancer incidence and urge further studies to determine the relationship between the dietary intake of
specific fatty acids and breast cancer risk.
Simonsen, Neal, et al. Adipose tissue omega-3 and omega-6 fatty acid content and breast cancer in the
EURAMIC Study. American Journal of Epidemiology, Vol. 147, No. 4, 1998, pp. 342-52
Fat consumption and cancer
LONDON, UNITED KINGDOM. Several major epidemiologic studies have found a clear association
between a high dietary fat intake and the risk of developing breast and colon cancer. The correlation is
particularly strong in the case of animal fats. One study found that a high fish or fish oil consumption is
protective against later stage colon cancer in men, but has no effect on mortality from breast cancer.
British medical researchers now report that fish and fish oils not only protect against colon cancer in men,
but also against colon and breast cancer in women. This protective effect, however, is only apparent in
countries where the intake of animal fats is high. In other words, a high intake of fish or fish oils
counteracts the detrimental effects of a high animal fat consumption.
The study compared cancer mortality rates in 24 European countries, Canada and the USA with fish
consumption and the intake of animal fats. In countries where the animal fat intake was high the
researchers found a clear inverse correlation between the ratio of fish fat to animal fat and the risk of
developing breast cancer in women and colon cancer in both men and women. A similar correlation was
found between cancer risk and the ratio of fish fat to total fat intake.
The researchers conclude that a 15% decrease in animal fat intake combined with a 3-fold increase in
fish oil intake could possibly reduce male colon cancer risk by as much as 30% in countries with a high
animal fat intake. A 3-fold increase in fish oil intake could be achieved by eating fish three times a week
or by taking two standard fish oil capsules daily.
Caygill, C.P.J., et al. Fat, fish, fish oil and cancer. British Journal of Cancer, Vol. 74, No. 1, July 1996,
pp. 159-64
