I’ve previously discussed the role of dietary lignans in the reduction of breast cancer risk and improvement in breast cancer survival, based on studies like this that showed that women with breast cancer who ate the most lignans appeared to live longer, but lignans are found throughout the plant kingdom—seeds, whole grains, vegetables, fruits, berries—so how do we know lignans weren’t just a marker for the intake of unrefined plant foods? For example, those that eat lots of plants, vegetarians, have about 8 times the lignan intake of omnivores, and the one that ate the most plants, the vegan, was off the charts.
Well in a petri dish, lignans were shown to not only have direct anticancer growth activity against human breast cancer cells, but also prevent their migration, so it was finally put to the test. A randomized double-blind placebo-controlled clinical trial of flaxseeds, the world’s most concentrated source of lignans, in breast cancer patients found that flax appears to have the potential to reduce human breast tumor growth in just a matter of weeks. So I started recommending ground flax seeds to breast cancer patients, but what about preventing breast cancer in the first place?
Similarly, high lignan intake was associated with reduced breast cancer risk, but maybe that’s just saying high plant food intake help in general. So they gave women at high risk for breast cancer a teaspoon of ground flaxseeds a day for a year, and they showed, on average, a drop in precancerous changes. But what about flax seeds and breast cancer itself? Outside of an experimental setting there just weren’t a lot of women eating flax seeds regularly to study, until now. Matching 3,000 women with breast cancer to 3,000 women without, they found consumption of flaxseed alone, and of flax bread, was associated with a 20–30% reduction in breast cancer risk.
As flaxseeds are packed with lignans, only a small daily serving of flaxseed is required to attain the level of lignan intake associated with a reduction in breast cancer risk. As it appears that most women do not consume flaxseed and that small amounts may be associated with reduced breast cancer risk, we might want to consider interventions to increase the prevalence of flaxseed consumption.
The latest review summarized the association between flax and decreased risk of breast cancer in the first place, better mental health, and lower mortality among breast cancer patients. The only other study of flax and brain health I’m aware of was an exploration of 100 commonly used drugs and supplements on cognition in older adults, that found flax to be one of the few things that appeared to help.
In terms of why flaxseeds may play a role in preventing and treating breast cancer, there’s an inflammatory molecule called interleukin-1, which may help tumors feed, grow, and invade, so our body produces an interkeukin-1 receptor antagonist; it binds to the IL-1 receptor and blocks the action of IL-1. And the activity of this protective inhibitor can be boosted with the drug tamoxifen or by eating flax seeds. In premenopausal women, the pro-inflammatory profile of interleukin-1 could be counteracted by a dietary addition of a few spoonfuls of ground flax. One month of flax was able to increase the anti-inflammatory inhibitor levels by over 50%, better than even the drug.
Yes, having one’s ovaries removed may reduce breast cancer risk as much as 60%, but at the cost of severe side-effects. The drug tamoxifen may reduce the incidence of breast cancer by more than 40% but may induce other severe side effects such as uterine cancer and blood clots. That’s why less toxic, even safe, breast cancer preventive strategies such as diet modifications need to be developed, and these lignin phytoestrogens in flaxseeds may be one successful route because of very recent epidemiological data.
Now lignans are not a magic bullet to prevent breast cancer—you can’t just sprinkle some flax on your bacon cheeseburger—but as a part of a healthy diet and life-style they might help to reduce breast cancer risk in the general population.
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.
Please consider volunteering to help out on the site.