Could taking fish oil supplements help lower cancer risk?

For this study, researchers analyzed medical data from more than 250,000 people listed in the UK Biobank who were followed for more than 10 years, focusing on the presence of omega-3 and omega-6 in their blood and the incidence of 19 specific types of cancer.

“There has been strong interest in the health benefits of omega-3 and omega-6 fatty acids,” Kaixiong ‘Calvin’ Ye, PhD, associate professor in the Department of Genetics in the Franklin College of Arts and Sciences at the University of Georgia and corresponding author of this study told Medical News Today.

“However, finding conclusive evidence has been hard mainly because, one, it is very difficult to accurately measure their dietary intake — self-reported dietary intake or fish oil supplementation is not accurate or biased. (And) two, a large study sample is needed, and this sample needs to be followed for many years to have sufficient numbers of disease incidences,” he said.

“Fortunately, we have access to a longitudinal cohort of over 500,000 participants, the UK Biobank study. These participants have been followed for about 13 years. In about 250,000 participants, there are measurements of the blood levels of omega-3 and omega-6 fatty acids. These measurements are objective biomarkers, reflecting one’s dietary intake of omega-3 and omega-6 fatty acids,” Ye continued.

“One of our previous studies used this cohort. It was found that individuals with higher levels of omega-3 and omega-6 are less likely to die because of cancer. Compared to individuals with the lowest levels, those with the highest levels of omega-3 (or omega-6) are 20% less likely to die of cancer. In the current study, we asked if omega-3 and omega-6 fatty acids are related to new incidence of cancer,” he added.

About 30,000 study participants developed cancer during the study period.

Of the 19 types of cancer Ye and his team focused on, they found that higher blood levels of both omega-3 and omega-6 were correlated to a lower incidence of cancer overall.

Study participants with high levels of omega-3 in their blood had lower rates of developing digestive system cancers — including colon and stomach cancers — as well as lung cancer.

Those with higher levels of omega-6 had a decreased risk of developing 14 of 19 cancers, including brain, thyroid, kidney, bladder, lung, pancreatic, and colon cancers.

“Our study painted a big picture about the protective associations of both omega-3 and omega-6 fatty acids with cancer incidence, including overall cancer and 14 out of 19 specific cancer types. In general, these findings support the increased intake of unsaturated fats — that is, omega-3 and omega-6 fatty acids — to reduce cancer risk.”
— Kaixiong ‘Calvin’ Ye, PhD

“Future studies need to address the differences between omega-3 and omega-6 across the cancer types. Of note, prostate cancer is the only cancer type that is against the overall trend and shows positive associations with omega-3. We are not the [first] study to report this risk-increasing association, but the underlying explanation is unknown,” Ye said.

“Moreover, we found that the protective associations of omega-3 with overall cancer are stronger in the younger age group and in the women. On the other hand, the protective associations of omega-6 with overall cancer are stronger in the older age group, in the men, and in current smokers. Future research should address these different effects in population subgroups,” Ye added.

After reviewing this study, Nilesh Vora, MD, a board certified hematologist, medical oncologist, and medical director of the MemorialCare Todd Cancer Institute at Long Beach Medical Center in Long Beach, CA, told MNT that he found its findings thought-provoking.

“I think it’s very interesting to think about the question that we’re always asked, which is how does diet and what we intake influence the risk of cancer? And so this is one of the first studies where there may very well be an association,” Vora said.

“The cancer incidence is going up in our society and the question is how do we lower that?,” he continues. “And this becomes one of the important ways to really make that determination is to look at dietary changes, look at protective variables to us, and be able to advise patients out there, to educate patients out there, on the importance of living as healthy a lifestyle as possible.”

For next steps in this research, Vora said he would like to see clarification on how omega-3 and omega-6 fatty acids might help lower cancer risk, as well as whether or not this research can broadly be applied to other societies.

“If you look at the demographic that (they were) working with, it’s more of a narrower demographic. So I think we definitely need to say, can we also repeat this study in other populations and draw from this to be able to say it’s not just people in the United Kingdom who benefit from this, like European ancestry, white ethnicity, it’s also in a broader segment of the population,” he explained.

MNT also spoke with Monique Richard, MS, RDN, LDN, a registered dietitian nutritionist (RDN) and owner of Nutrition-In-Sight, about this study.

“I was not surprised by the findings of this study since it has been pretty well established that consuming sources of a variety of healthy fatty acids are essential to whole-body health and have been attributed to the prevention and reduced risk of cancer, chronic disease, and other conditions associated with inflammation and cellular health. They also support blood vessel health and cognitive function,” Richard explained.

“Foods that are rich in omega-3 and omega-6 fatty acids — fish, nuts, seeds, and various sea plants — are also packaged with so many other beneficial nutrients such as protein, minerals, and vitamins such as potassium, selenium, calcium, (and) vitamins E, A, and D to name a few. All of these work together to support health and optimal systemic and cellular function.”
— Monique Richard, MS, RDN, LDN

For readers looking to increase their intake of essential fatty acids, Richard advised focusing on “food first” as the primary source for meeting our basic macro- and micronutrients, if possible.

“With the option of supplementation as a compliment, not a replacement, when applicable, related to a condition, physiological circumstance, increased need, deficiency, or other applicable factor when appropriate,” she added.

According to Richard, foods rich in omega-3, omega-6 fatty acids, or both include:

• Plant sources:
  • flaxseed
  • chia seed
  • walnuts
  • soybeans
  • hemp seeds
  • seaweed
  • algae
  • wheat germ
  • sunflower seeds
  • tofu
  • spinach and green leafy vegetables
  • purslane
• Animal sources, especially cold-water fish, which are lower in mercury, are rich sources of omega-3 fatty acids. Two servings (3-4 ounces per serving) a week for an average adult is a recommended serving amount. To remember some beneficial sources, think of the acronym S.M.A.S.H.
  • salmon
  • mackerel
  • anchovies
  • sardines
  • herring
• As well as
  • tuna
  • trout
  • cod and other varieties of fish

“The ratio of omega-6 fatty acids to omega-3 fatty acids and the quality of their source do also play a significant role in if these nutrients will be beneficial, or consequential — along with various factors unique to that person such as the microbiome health and genetics,” Richard said.

“It is important to understand what to look for when considering a supplement, the amount that may be appropriate for you, purpose, and duration. Working with an RDN, pharmacist, and your healthcare team together to learn what may be best for you as an individual is vital,” she added.