Please read Mercola's article as well as listening to the video particularly the section
10 Simple Lifestyle Strategies to Reduce Your Risk of Breast Cancer
While this provides the basis for a cancer prevention protocol I think we should remember that diabetes is associated with an increased risk of breast cancer. It follows that everything we can do to prevent Diabetes will also reduce BC risk
Assessing Insulin Resistance Can Inform About Breast Cancer Risk
Therefore in addition to the suggestions from Dr Mercola it may help to understand insulin resistance nearly doubles the risk of breast cancer (and diabetes) so improving insulin sensitivity may be a useful strategy to reduce risk and/or improve prognosis.
Homeostasis model assessment to detect insulin resistance and identify patients at high risk of breast cancer development
Dr Mercola mentions vitamin D3 but doesn't point out that in people who are magnesium deficient or insufficient Vitamin D doesn't function optimally. Vitamin D requires is Cofactors the most important on is MAGNESIUM
Magnesium intake decreases Type 2 diabetes risk through the improvement of insulin resistance and inflammation
Having acidosis or a diet which produces higher levels of acidity, causes the body to excrete magnesium in urine. Most of us don't reach the current Magnesium RDA so losing the little magnesium we have down the loo means that even with higher Vitamin D levels we can't make best use of that vitamin D.
Inverse relationship between vitamin D status and insulin resistance The Mercola article has sensible advice for improving Vitamin d level.
Dr Mercola mentions omega 3
Dietary Omega-3 Fatty Acid Deficiency and High Fructose intake in the Development of Metabolic Syndrome This explains how low omega 3 levels are linked to higher levels of insulin resistance.
Mercola also mentions
Get proper sleep
This paper
Nocturnal melatonin secretion is independently and inversely associated with insulin resistance. explains why it's helpful in improving insulin sensitivity and therefore why it will help reduce risk factors for diabetes and Breast cancer (and Dementia)
All of these approaches need to be deployed at the same time as they all work better together than indiviually. Omega 3 like magnesium works on it's own but also improves the action of Vitamin D.
I should perhaps have put more emphasis on Mercola's injunction
Radically reduce your intake of sugar/fructose and processed foods.
If you continue to eat foods that raise glucose levels (forcing higher insulin production) high and fast then you will continue to create the inflammation that is driving the initiation of DNA damage. Similarly if we want to benefit from omega 3 improvements we have to reduce sources of omega 6 as the pro inflammatory nature of omega 6 inevitably overwhelms to ability of omega 3 to resolve inflammation.
Edit:
I forgot to mention that although Dr Mercola says in relation to increasing vitamin d levels
""which would necessitate increasing your intake of vitamin K2 as well, either from food or a supplement."
Increasing
Vitamin K2 Supplementation Improves Insulin Sensitivity
So improving vitamin K should be considered in it's own right as well as an adjunct to Vitamin d supplements.