A high dietary intake of omega-3 fatty acids, derived from oily fish, may help to lower the risk of death from colorectal cancer in patients diagnosed with the disease.
If the new findings are reproduced in other studies, people with bowel cancer might benefit from increasing their oily fish intake to help prolong their survival.
Previous experimental research has shown that omega-3 fatty acids --namely, eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and docosapentaenoic acid (DPA)--can suppress tumour growth and curb blood supply to malignant cells (angiogenesis).
The researchers based their findings on participants of two large long-term studies: the Nurses' Health Study of 121,700 US registered female nurses, aged between 30 and 55 in 1976; and the Health Professionals Follow Up Study of 51, 529 male health professionals, aged between 40 and 75 in 1986.
All participants filled in a detailed questionnaire about their medical history and lifestyle factors when they joined the studies, and this was repeated every two years subsequently.
The information collected included any diagnosis of bowel cancer and potential risk factors, such as height, weight, smoking status, regular use of aspirin and non-steroidal inflammatory drugs and exercise level.
Data on what they ate were also collected and updated every four years.
Among 1659 participants who developed bowel cancer, 561 died; 169 of these were classified as deaths from the disease during an average monitoring period of 10.5 years. Other major causes of death included cardiovascular disease (153) and other cancers (113).
Participants with a higher dietary intake of omega 3 from oily fish were more likely to be physically active, take multivitamins, drink alcohol and to consume more vitamin D and fibre. They were also less likely to smoke--all factors associated with a lower risk of bowel cancer.
A daily intake of 300 mg omega-3’s – about 3.5 ounces of salmon per week – linked to lower risk of colon cancer death
But those who had been diagnosed with bowel cancer and whose diets contained higher levels of omega-3’s from fatty fish had a lower risk of dying from the disease.
The extent of the reduced risk seemed to be linked to the amount of omega-3’s consumed, with higher doses associated with lower risk. This held true even after taking account of intake prior to the diagnosis, as well as other risk factors.
Compared with patients who consumed less than 0.1 g of omega 3 fatty acids daily, those who consumed at least 0.3 g daily after their diagnosis, had a 41% lower risk of dying from their disease. (Three ounces of salmon, for example, contains 1.8 g of omega-3 fatty acids.)
Where to get your omega-3’s
This reduced risk applied to food sources and supplements, although few people in the study used omega 3 fish oil supplements). Oily fish like salmon, trout, sardines, anchovies, mackerel and herring are the best sources of omega-3 fatty acids.
The protective effect of omega-3 intake seemed to be particularly beneficial among those who were tall, who were not overweigh, or who didn't take regular aspirin.
Increasing omega-3 intake by at least 0.15 g daily after diagnosis was associated with a 70% lower risk of dying from bowel cancer. Omega-3 fats store in the body, so to increase intake by 0.15 g per day requires eating roughly an extra two ounces (60 g) of salmon each week.
This is an observational study so no firm conclusions can be drawn about cause and effect, but the researchers say that their findings provide the first line of population based evidence for the potentially positive impact of oily fish omega 3 fatty acids on bowel cancer survival.
Source: Gut, July 2016.
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