Scientists have now published more than 700 scientific papers on vitamin D and breast cancer. More to the point, 37 clinical trials on the topic are now currently registered, all looking to answer two questions: Does vitamin D help prevent breast cancer, and two, does vitamin D have any treatment effect in established breast cancer?
If you read the obituaries in your local newspaper, you will find numerous women, dead in their 40s and 50s, dead before their time, and too often, the culprit is breast cancer. The lifetime risk for breast cancer in the USA is around 10% of women by age 90, with a 3% lifetime risk of dying from breast cancer. For unknown reasons, the United States has the highest rates of breast cancer in the world; 128 per 100,000 in whites, slightly less among African Americans. Breast cancer is the only major cancer that is less common in Blacks, but the disease is more aggressive in Blacks. It is the second-most common cause of cancer death (after lung cancer) in women. In 2010, breast cancer caused in excess of 40,000 deaths in the USA.
Dr. Theresa Shao and colleagues at the Beth Israel Medical Center published a great review paper in January of 2012.
Other than the Lappe paper (in which 1,100 IU of vitamin D appeared to prevent a number of internal cancers), we have no randomized controlled trials to answer the questions above. Interested women everywhere must understand what is known and what is unknown and make up their own minds. As readers know, I am a great believer in waiting for the science to do its work with a natural vitamin D level (around 50 ng/ml).
First, the authors reviewed the test tube and animal studies. They are impressive. Vitamin D signals more than 100 genes to force breast cells to die (which is natural), prevent them from being undifferentiated, and prevent them from hijacking blood vessels. Therefore, animal and test tube studies are generally quite positive.
Next are ecological studies or the study of the relationships living things have to one another. Here again we have multiple studies showing areas with the most sunlight have the lowest rate of breast cancer. After that, we have dietary studies, which are virtually all negative because you simply cannot get enough vitamin D from your diet to make any significant difference.
Then we have at least eight studies of vitamin D levels and subsequent risk of breast cancer. Here, five of the eight are supportive, and two of the three negative studies are very close to positive. Few of the studies had adequate levels. The one study with natural levels reported that women with levels of 60 ng/ml or greater were almost six times less likely to get breast cancer than women whose levels were less than 20 ng/ml. As you’d suspect it was a small study: how can you find enough women with natural levels?
Then the authors discuss several studies that show women diagnosed in the summer do better than women diagnosed in the winter, a finding suggestive of a treatment effect. Another study showed that women diagnosed with breast cancer had a better prognosis if their vitamin D levels were higher, supportive of the season-of-diagnosis findings. Unfortunately, no randomized controlled trial giving meaningful doses of vitamin D, except the Lappe study, have ever been published.
An interesting study gave women with breast cancer 50,000 IU/week and found that women who achieved a blood level of greater than 60 ng/ml had less disability from joint symptoms, a common complaint with standard breast cancer therapy.
Then, Dr. Theresa Shao and colleagues at the Beth Israel Medical Center then did something quite amazing. They did not end their paper with the truism that we don’t know if vitamin D will help and more studies are needed. Instead they wrote,
“The optimal risk for reducing breast cancer risk or the risk of recurrence of breast cancer has yet to be defined, but simply targeting 25(OH)D levels known to be safe and optimal for bone health (30-50 ng/ml) might be a good start.”
I could not have said it better, although natural levels, around 50 ng/ml, might be a better start than the levels found in indoor workers in the summer (30 ng/ml). I hope the author’s summation represents a change in how scientists view cancer and vitamin D. Moreover, I hope they add a little common sense to the subject, unlike the “do nothing until randomized controlled trials prove it helps” crowd; a crowd whose hands increasingly look bloody to me.