Let’s be clear. No single food or nutrient constitutes a miracle cure.
That said, omega-3s from seafood clearly support heart, eye, and brain health, and bring anti-inflammatory benefits.
And many are surprised to hear about evidence linking oceanic omega-3s to better cancer and bone health outcomes — which just grew stronger.
New research — a Canadian rodent study and an Iranian evidence review — add encouraging evidence about omega-3s, breast cancer, and bone health.
Before we dive in, let's review what's known about omega-3s and cancer, and the difference between omega-3s from land and sea, which was the subject of the new breast-cancer study.
Omega-3s versus cancer: a quick overview
Cancer comes in hundreds of distinct forms — each of which may react differently to nutrients or drugs.
The benefits of chemotherapy drugs are typically limited to one type of malignancy, or to a few types that fall into the same category.
Growing laboratory, statistical, and clinical evidence indicates that fish-heavy diets — and/or seafood-source omega-3 fats — can reduce the risk for some cancers, and/or make chemotherapy more effective.
To view our past coverage of research about omega-3s’ potential anti-cancer effects on specific types of tumors, search our website for “omega-3 cancer”.
Because the new omega-3/breast-cancer study compared the effects of seafood-source and plant-source omega-3s, let’s quickly review the key differences between them.
Two distinct omega-3 families: Seafood-source and plant-source
Omega-3s fall into two categories, with distinctly different health impacts.
The body uses EPA and DHA for critical bodily functions, and it can only make very small amounts of these from ALA, the sole plant-source omega-3.
Unsurprisingly, all the available evidence suggests that people should get as many seafood source omega-3s — especially DHA — as possible from fish, shellfish, and/or or supplements:
On average, people can only convert about five percent of the ALA in plant foods or oils into long-chain omega-3s.
That conversion process primarily produces EPA, and much smaller amounts of DHA, which is the more important of the two, because we can easily convert DHA into EPA, but can’t easily convert EPA into DHA.
Although there’s growing evidence that dietary omega-3 ALA delivers significant health benefits — even without being converted into EPA or DHA — but it’s crystal clear that in terms of health benefits, the major omega-3 players are DHA and EPA.
And the voluminous evidence that favors dietary EPA and DHA over dietary ALA just gained significant support from a new breast-cancer study from Canada.
Fishy omega-3s beat plant-source counterparts in Canadian breast-cancer study
Researchers from Canada’s University of Guelph conducted the study, led by Prof. David Ma.
As Dr. Ma said, “There is evidence that both omega-3s from plants and marine sources are protective against cancer … this study is the first to compare the cancer-fighting potency of plant- versus marine-derived omega-3s on breast tumor development.”
Perhaps unsurprisingly, the Canadians found that seafood-source DHA and EPA packed a stronger anti-cancer punch than omega-3 ALA from vegetable oils (Liu J, Ma DW 2017).
The Canadian team found seafood-source omega-3s eight times more effective at inhibiting the development and growth of breast tumors in mice.
They tested the effects of dietary DHA and EPA in mice with a highly aggressive form of estrogen receptor-positive human breast cancer called HER-2 — which constitutes 20-25 percent of human breast-cancer cases, and has a poor prognosis.
Then, they divided the mice into two groups, and fed each group either seafood-source or plant-source omega-3s — and they started by feeding the animals' pregnant mothers omega-3s.
“The mice were exposed to the different omega-3s even before tumors developed, which allowed us to compare how effective the fatty acids are at prevention,” said Dr. Ma.
And the Canadian team found that feeding the mice and their pregnant mothers seafood-source omega-3s reduced the size of breast tumors by 60 to 70 percent and reduced the number of tumors by 30 percent.
In contrast, it took much higher doses of plant-source omega-3 ALA to exert the same beneficial effects.
Prof. Ma made an important point: “In North America, we don’t get enough omega-3s from seafood, so there lies an opportunity to improve our diet and help prevent the risk of breast cancer.”
He expressed hope that their findings would have broader applications: “Seeing the significant benefits omega-3s can have in combatting a highly aggressive form of breast cancer means omega-3s will likely be beneficial for other types of cancer.”
Based on the doses given in the study, Ma said, people should eat two to three servings of fish per week to enable similar potential benefits.
And, as the professor noted, you can get DHA and EPA from fish oil supplements and obtain DHA from DHA-fortified eggs or milk.
According to Prof. Ma, omega-3s prevent and fight cancer by turning on genes associated with the immune system and blocking tumor growth pathways.
In addition, inflammation is known to promote cancer, and mice and people alike use seafood-type omega-3s to moderate and end inflammation.
Fishy omega-3s linked to bone health in Iranian study
Recently, Iranian scientists analyzed 19 studies that examined the effects of dietary fish or seafood-source omega-3s on bone health.
Prior findings on the subject hadn’t been consistent, so they conducted two separate analyses — a systematic review and a meta-analysis — to see whether it’s possible to come to a clear conclusion at this point.
Encouragingly, they found good evidence linking higher intakes of fish or seafood-source omega-3 fatty acids to significantly reduced risks for hip fractures (Sadeghi O et al. 2017).
Using study quality as their criteria, they selected 10 epidemiological studies — seven prospective and three case-control — for their systematic review, and nine studies (with 292,657 participants) for their meta-analysis.
The results of their analysis linked higher fish consumption to a 12% reduction in the risk of hip fracture. Those findings applied specifically to prospective studies with at least 10,000 participants, and to studies that considered each participant’s body mass index (BMI).
Likewise, their analysis linked higher intakes of seafood-source omega-3s to an 11% reduction in the risk of hip fracture.
As they wrote, “We found that [higher] fish consumption and dietary intake of omega-3 fatty acids might have protective effects on bone health and [reduce] the risk of hip fracture.”
To view our past coverage of research about omega-3s’ potential effects on bone health, search our website for “omega-3 bone”.