There have been many studies demonstrating a lower risk of breast cancer diagnosis and death when women raise their serum 25(OH)D levels. The similar findings between all these studies emphasizes the importance of improving vitamin D status for reducing the risk of breast cancer and increasing chances of survival with diagnosis. Below are some of the key published findings on the topic of breast cancer and vitamin D, followed by other nutrients and lifestyle habits that may also play an important role in reducing the risk of breast cancer and improving breast cancer outcomes.
Reduced Risk of Breast Cancer Diagnosis – Reduced Risk of Breast Cancer Recurrence & Death
Breast Cancer and Vitamin D – Summary of Research
A 2005 study by Lowe et al. included 179 breast cancer patients and 131 controls (women without breast cancer), and found that women with vitamin D levels above 60 ng/ml (150 nmol/L) had an 83% lower risk of breast cancer than women with concentrations less than 20 ng/ml (50 nmol/L) (P<0.001).
In 2007, Abbas et al. matched 1,395 cases of women with breast cancer with 1,365 controls. Researchers found a distinct correlation between vitamin D levels and breast cancer risk, where vitamin D levels greater than or equal to 30 ng/ml had an almost 70% reduced risk of post-menopausal breast cancer compared to those with levels less than 12 ng/ml.
82% Lower Breast Cancer Risk with Vitamin D Level of 60 vs. 20 ng/ml (McDonnell et al. – Analysis #1)
A 2018 pooled analysis of a randomized trial and a prospective cohort study by McDonnell et al. involved women who were 55 years of age or older. 3 different analyses of the data showed similar results when comparing risk reduction between women with a vitamin D level of 60 ng/ml or higher and women with a vitamin D level of 20 ng/ml or less. The first analysis showed women with a vitamin D serum level of 60 ng/ml or greater had an 82% reduced risk of breast cancer compared to those with a vitamin D level of 20 ng/ml or less.
78% Lower Breast Cancer Risk with Vitamin D Level of 60 vs. 20 ng/ml (McDonnell et al. – Analysis #2)
Another analysis from that paper compared the percent of breast cancer-free participants (i.e. those without breast cancer) by vitamin D group. This analysis accounted for vitamin D levels of participants changing over time and for varying lengths of study participation. This analysis showed that for each group of vitamin D, as levels increased, the percent of participants with breast cancer was lower. Specifically, at 4 years the percent of participants with breast cancer was 78% lower for women with vitamin D levels at or above 60 ng/ml (150 nmol/L) compared to women with levels less than 20 ng/ml (50 nmol/L).
80% Lower Breast Cancer Risk with Vitamin D Level of 60 vs. 20 ng/ml (McDonnell et al. – Analysis #3)
The third analysis from that paper quantified the association between vitamin D level and breast cancer risk after adjusting for age, BMI, smoking status, and calcium supplement intake. This analysis revealed that women with vitamin D levels at or above 60 ng/ml had an 80% lower risk of breast cancer than women with levels less than 20 ng/ml. All three analyses showed similar results – higher vitamin D levels were associated with decreased breast cancer risk, with levels at or above 60 ng/ml being the most protective!
Additionally, since breast cancers diagnosed in the first year were likely present but undiagnosed at the beginning of the study, we also repeated the analysis with only those without breast cancer at one year. We found that those with vitamin D levels at or above 60 ng/ml had a 93% lower risk of breast cancer compared to women with levels less than 20 ng/ml.
A 2019 meta-analysis by Song et al. analyzed data from 70 observational studies, and found a dose response relationship between vitamin D level and breast cancer risk. Specifically, the researchers found a 6% decrease in breast cancer risk for every 2 ng/ml (5 nmol/L) increase in vitamin D level. This translates to a 71% lower risk from 20 to 60 ng/ml (50 to 150 nmol/L).
Other Studies Showing a Reduced Risk of Breast Cancer with Vitamin D
A 2013 case control study at UCSD School of Medicine, Mohr et al. found that the three months prior to tumor diagnosis was a relevant window of time for cancer prevention and that those with vitamin D levels ≥35 ng/ml had a 70% reduction in risk of developing breast cancer than those with levels <15 ng/ml.
Bilinski et. al. demonstrated in a 2013 case control study that women with 25(OH)D levels ≥30 ng/ml had an almost 60% reduction in risk of breast cancer compared to those with levels <10 ng/ml. Among women younger than 50 years old, there was a 71% reduction in risk and among women 50 years and older there was a 55% reduction in risk.
In a 2012 case control study, Yao et. al. found that women with 25(OH)D levels ≥30 ng/ml had more than a 60% reduction in breast cancer risk compared to women with levels <20 ng/ml. Among post-menopausal women, there was a 71% reduction.
In a 2012 case control study, Peppone et. al. found that those with 25(OH)D levels ≥32 ng/ml had an almost 60% reduction in breast cancer risk compared to women with levels ≤20 ng/ml.
In a 2009 case control study, Abbas et al. found that women with 25(OH)D levels ≥24 ng/ml had more than a 50% reduction in risk of pre-menopausal breast cancer compared to those with levels <12 ng/ml.
In a 2009 case control study, Rejnmark found that pre-menopausal women with 25(OH)D levels ≥34 ng/ml had more than a 60% reduction in breast cancer risk compared to women with levels <24 ng/ml.
In a 2009 case control study, Crew et. al. found that post-menopausal women with 25(OH)D levels ≥40 ng/ml had more than a 50% reduction in breast cancer risk compared to women with levels <20 ng/ml.
Reduced Risk of Breast Cancer Death with Vitamin D Levels At or After Diagnosis
A 2014 analysis of five studies by Mohr et al. sought to determine the relationship between vitamin D level and breast cancer survival among women already diagnosed with breast cancer. Compared to patients in the group with the lowest vitamin D levels (an average of 17 ng/ml or 42 nmol/L), breast cancer patients in the group with the highest vitamin D levels (average of 30 ng/ml or 75 nmol/L) had a 44% lower risk of breast cancer related death. In fact, when looking at the direct relationship between vitamin D level and breast cancer fatality, the vitamin D level accounted for 97% of the variance.
Yao et al. summarized initial findings from a 2021 study involving women diagnosed with incident invasive breast cancer between 2006 and 2013, and their risk of death. This study found that women whose vitamin D level at the time of diagnosis was 30 ng/ml (75 nmol/L) or higher had a 27% lower risk of death compared to women whose vitamin D level was below 20 ng/ml (50 nmol/L). In this study, black women had the lowest vitamin D levels, which the authors suggest is a major contributor to their poorer survival outcomes.
Madden et al. published results from a 2018 study assessing the relationship between vitamin D supplement use, initiated after a breast cancer diagnosis, and associated mortality. Overall, there was a 20% lower risk of death from breast cancer among those who started using vitamin D supplements after diagnosis compared to those who didn’t (P=0.048). If vitamin D supplementation was initiated within 6 months of diagnosis, there was a 49% lower risk (P<0.001).
Breast Cancer and Other Nutrients – Summary of Research
A 2013 meta-analysis of 21 studies on omega-3s and risk of breast cancer by Zheng et al. concludes that higher consumption of omega-3s corresponds with a lower risk of breast cancer. The figure below shows that as dose of omega-3s (shown as % energy intake per day) increases the relative risk of breast cancer decreases (p=0.011).
A 2019 study by Huang et al. recruited 1050 breast cancer patients and 1229 controls (women without breast cancer) in China and collected information about dietary magnesium intake. There was a 40% decrease in breast cancer risk for those with the highest dietary magnesium intake vs the lowest.
Huang et al. found a 22% reduction in breast cancer risk associated with those whose magnesium intake was at least 280 mg/day compared to those whose magnesium intake was lower than 280 mg/day.
A subgroup had serum measurements of CRP taken as a marker of inflammation. Those with CRP levels less than 3000 ng/mL had a 30% lower risk of breast cancer than those with levels at or above 3000 ng/mL. Dietary magnesium was found to have both a direct association and an indirect association with breast cancer risk.
Demircan et al. looked at breast cancer outcomes among 1996 patients with primary invasive breast cancer and correlated them to selenium status. Three different biomarkers of selenium (Se) were utilized: total serum Se concentration, selenoprotein P (SELENOP), and the glutathione peroxidase GPx3. Selenium status was divided into quintiles for each. The highest risk of mortality was seen among those with the lowest selenium status, and the relationship was strongest when selenium status was lowest according to all three measurements combined. Patients with the highest serum Se concentrations had a 58% lower risk of death compared to patients with the lowest serum Se concentrations.
When considered together, all three selenium biomarkers were better at predicting mortality than three of the most important tumor characteristics.
A 2014 meta-analysis by Harris et al. looked at data from ten different studies with a total of 17,696 breast cancer cases to determine what type of effect vitamin C intake, from supplements and from the diet, had on breast cancer survival rates. Among those who took vitamin C supplements after a diagnosis of breast cancer, there was a 19% decreased risk of dying overall, and a 15% reduced risk of dying specifically from breast cancer.
When taking a closer look, for each 100 mg per day increase in dietary vitamin C intake, there was a 27% reduced risk of dying overall, and a 22% decreased risk of dying specifically from breast cancer. Among studies that included data in groups of “high” and “low” vitamin C intake, there was a 20% reduced risk of total mortality and a 23% reduced risk of breast cancer specific mortality in the “high intake” groups compared to the “low intake” groups.
Breast Cancer and Lifestyle Habits – Summary of Research
A study by Pedersen et al. included data from 38,375 Danish women, 70 years of age or younger, who had been diagnosed with breast cancer, and 191,875 controls who were breast cancer free. They looked at the employment history of all the women to see if there was a correlation between breast cancer incidence and long-term, occupational UV exposure. They found a 17% decreased risk for late-onset cancer (diagnosed at 50 years or older) with longer duration of UV exposure (more than 20 years exposure) and a 11% decreased risk with higher cumulative UV exposure (top 25% percentile of exposure). Also, the researchers found a 15% decreased risk overall associated with longer duration of UV exposure (more than 20 years) for all diagnosis ages combined.
A dose-response meta-analysis on UV exposure and breast cancer risk, by Yilun Li and Li Ma, aimed to quantify the relationship between the amount of UV exposure and breast cancer risk. They included six case-control studies and conducted a dose-response meta-analysis, with an additional analysis by age, sunscreen use, and limb coverage. The authors found a significant dose-response correlation between UV exposure and breast cancer risk such that women in the highest exposure groups had a 30% lower risk of breast cancer compared to women in the lowest exposure groups. A significant dose-response relationship in women over 40 years of age was found which showed a breast cancer risk reduction of 10% for each increase of 1000 mW/m2 hours in the dose of sunlight. Women who did not tan or who covered their arms and legs while in the sun had a higher risk of breast cancer.
A review by Buja et al., which analyzed 48 different studies to assess the association between specific foods and dietary patterns and the risk of breast cancer, found that diets high in refined sugars, saturated fat, and alcohol (such as the Western Diet) increased breast cancer risk, while the Mediterranean diet, which is high in fish, fiber, healthy fats, vegetables, antioxidants and extra-virgin olive oil, was found to have a protective effect reducing the risk of breast cancer. This protective association was stronger among postmenopausal women, and when alcohol was excluded from the diet. A protective effect was also seen regardless of body weight and BMI among some studies.
As noted by Huang et al. above, CRP levels less than 3000 ng/mL had a 30% lower risk of breast cancer than those with levels at or above 3000 ng/mL. Research has established a consistent correlation between diet and inflammation, such as that done by Casas et al. on the Mediterranean diet (MedDiet). This particular study demonstrated the effects of diet on inflammation among 165 participants who had a high risk of cardiovascular disease. The participants were randomly split into three groups and had to follow a specific diet for 5 years: one group was put on a Mediterranean Diet supplemented with olive oil, another on a Mediterranean Diet with nuts (walnuts, almonds, and hazelnuts), and one on a low fat diet. Both groups on the Mediterranean Diet experienced decreased inflammation (as measured by hsCRP), while the low fat diet group did not.
Dydjow-Bendek et al. enrolled 201 newly diagnosed female breast cancer patients between the ages of 50 and 69 years, and 201 women of the same age without cancer to determine if dietary fat and fish intake had any association with the chances of getting breast cancer. The focus of the analysis was on the amount of polyunsaturated fats (PUFAs) in the total diet, as well as the omega-3 to omega-6 intake ratio and total fish intake. Of the women diagnosed with breast cancer, 15.4% did not consume any fish at all compared to only 5% of women without breast cancer. Women whose PUFA intake amounted to at least 10% of their total energy intake had a 60% lower risk of breast cancer compared to women who consumed less PUFAs, and women who ate fish had a 70% lower risk of breast cancer compared to women who did not eat fish.
According to Fabian et al., the average intake of omega-3 fatty acids EPA and DHA is approximately 100 mg/day (from fish or supplements), and the average intake of omega-6 fatty acid AA is around 250 mg/day (from foods such as eggs, meat, and poultry). In order to have a better balance of pro-inflammatory AA to anti-inflammatory EPA + DHA within the tissues and cells of our bodies, the authors estimate an intake of about 2,000 – 3,000 mg/day of EPA + DHA would be needed in order to reach an omega-6:omega-3 ratio that would result in lower levels of inflammation.
GrassrootsHealth scientists recommend an Omega-3 Index of 8% or higher, which may be more equivalent to an AA:EPA ratio of around 9 or less. A GrassrootsHealth analysis found that ~1,300 mg/day of EPA+DHA was needed for 50% of the population and ~1,900 mg/day was needed for 90% of the population to achieve and Omega-3 Index of 8%. To reach an AA:EPA ratio closer to 2 or 3 would likely require achieving a higher Omega-3 Index and a higher daily dose of omega-3s and lower intake of omega-6s.
Some risk factors common for many diseases that can be controlled to some extent include diet, exercise, weight, smoking, stress, and alcohol consumption. Health outcomes can be affected by taking steps to keep each of these risk factors within a healthy range. Genetic components and our environment can also affect our risk of many diseases. As with the benefit of vitamin D, each risk factor has a varying level of influence depending on the specific disease in question.
Could Your Overall Health Benefit from Vitamin D?
Make sure you know your vitamin D level, and take steps to keep it within a target of 40-60 ng/ml or 100-150 nmol/L! Through GrassrootsHealth Nutrient Research Institute, you can also test your essential elements magnesium, copper, zinc and selenium, toxins such as lead, mercury and cadmium, as well as your omega-3 levels, inflammation levels and thyroid stimulating hormone (TSH) level. Find out your levels today! Log on to the test selection page (click the link below) to get your tests and see for yourself if your levels can be improved.
Make sure you track your results before and after, about every 6 months!
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