03 Mar Complicated Effects of Omega-3 and Polyunsaturated Fats on Cardiovascular Diseases and Cancer
MedicalResearch.com Interview with:
Lee Hooper PhD, RD
Reader in Research Synthesis, Nutrition & Hydration
Norwich Medical School
MedicalResearch.com: What is the background for this study?
Response: Polyunsaturated fats are common healthy eating choices, and fish oil (long-chain omega-3 including EPA and DHA) and flaxseed (containing alpha-linolenic acid, ALA, a plant-based omega-3) supplements are commonly consumed. Worldwide cardiovascular disease was responsible for 37% of premature deaths due to non-communicable disease in 2012, and cancers were responsible for 27%. Small effects of omega-3 and polyunsaturated fats on cardiovascular diseases and cancers could have big effects on worldwide health.
MedicalResearch.com: What are the main findings? What should readers take away from your report?
Response: We found the balance between small effects on cardiovascular diseases and cancers very interesting. When we increase either omega-3 or total polyunsaturated fats we see some small benefits on cardiovascular health, and some small harms to cancer outcomes.
If 1000 people increase their long-chain omega-3 intake (by taking a fish oil, EPA or DHA supplement) for around 4 years then 6 of those people will not experience a heart attack or angina that they would have had otherwise. And 3 of those people will not die of a heart attack. But an extra 3 people will be diagnosed with prostate cancer.
The effects of increasing total polyunsaturated fats are similar but stronger. If 1000 people increase their polyunsaturated fat intake (by using polyunsaturated oils in cooking and a polyunsaturated margarine for spreading) for around 4 years then 19 of those people will not experience a heart attack or angina, of whom 5 would have died. But an additional 8 people will experience a cancer diagnosis of whom 2 would have died.
So for both long-chain omega-3 and total polyunsaturated fats we see small benefits on heart health, and small harms on cancer outcomes. Overall effects of increasing omega-3 are minimal, while effects of increasing polyunsaturated fats are protective, though the effects are small.
MedicalResearch.com: What recommendations do you have for future research as a result of this work?
Response: We need more trials of the health effects of eating more oily fish! Oily fish is rich in protein, energy, and a variety of useful micronutrients like iodine, selenium, calcium etc, as well as omega-3. Understanding the health effects of eating more oily fish would be very useful, and an ideal research topic.
There are several large ongoing trials of supplemental long-chain omega-3 fats (fish oil supplements). We suggest that given the minimal health effects suggested for omega-3 fats in the large number of trials to date, no further trials should be initiated until the ongoing trials have reported. Ongoing and completed trials should make data on baseline long-chain omega-3 intake, and details of deaths, cancer diagnoses, cardiovascular outcomes, diabetes, cognition, depression, inflammatory bowel disease, lipids, adiposity and blood pressure available, as well as other key health outcomes, regardless of their primary outcomes.
Further large and high-quality trials of alpha-linolenic acid (ALA, the plant-based omega-3, found in rapeseed or canola oil, soya oil, flaxseed oil and some nuts) carried out in lower- and higher-income countries, and that assess baseline ALA intake and use biomarkers to assess compliance would be helpful to clarify the health effects of ALA (on cardiovascular and cancer diagnoses and deaths).
MedicalResearch.com: Is there anything else you would like to add?
Response: Our research was funded by the World Health Organization. No other disclosures or conflicts of interest. Thank you!
Hanson, S., Thorpe, G., Winstanley, L. et al. Omega-3, omega-6 and total dietary polyunsaturated fat on cancer incidence: systematic review and meta-analysis of randomised trials. Br J Cancer (2020). https://doi.org/10.1038/s41416-020-0761-6
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