Colorectal cancer is the third most common cancer diagnosed in both men and women in the U.S., excluding skin cancer, according to the American Cancer Society. It’s expected lead to more than 49,000 deaths in 2016.
Previous research has shown that omega-3 fatty acids can supress cancer tumor growth.
The latest research looked at people enrolled in two longstanding U.S. health studies of 121,700 women and 51,529 men whose medical history and lifestyle were checked frequently.
The information included any diagnosis of colorectal cancer. The people in the study periodically reported their diets using food questionnaires.
In total, 1,659 of the people developed colorectal cancer during the study. Of them, 561 died.
Those who had colorectal cancer and whose diets contained higher levels of omega-3s from fish, such as salmon and mackerel, had a lower risk of dying from the disease.
Compared with patients who got less than 0.1 grams of omega-3 fatty acids daily, those who got at least 0.3 grams daily after their colorectal cancer diagnosis had a 41% lower risk of dying from their disease, the study found.
Also, eating more fish-derived omega-3s by at least 0.15 grams daily after diagnosis was associated with a 70% lower risk of dying from colorectal cancer, while a reduction in daily intake was associated with a 10% higher risk of death from the disease.
The researchers also found that those who had more fish oil in their diet were more likely to be physically active, take multivitamins, drink alcohol, and get more vitamin D and fiber, and they were less likely to smoke.
Fish that contain omega-3 fatty acids include oily fish such as salmon, mackerel, tuna, sardines, and bluefish. The American Heart Association recommends eating fish at least twice a week, particularly those that are high in omega-3 fatty acids.
The authors of the study, published in the journal Gut, point out this was an observational study and no firm cause and effect conclusions can be drawn.
Eating More Fish and Less Meat
"It is not possible to attribute the lower risk of [colorectal] cancer specifically to omega-3 fatty acids because vitamin D may also have protective effects against colorectal cancer,” says Tom Sanders, professor emeritus of nutrition and dietetics at King's College London, in a statement. “People who eat fish may eat less of other foods linked to risk such as red and processed meat.”
It is worth noting that those who got more omega-3s also did other things that may boost colorectal cancer survival, such as being more likely to exercise, not smoke, and get more vitamin D and fiber, says Alister McNeish, lecturer in pharmacology at the University of Reading.