Vitamin D Aromatase Inhibitor

According to an animal and cell study that endocrinologists at Stanford University published in Endocrinology, the active form of vitamin D – calcitriol – is an anti-oestrogen. The study is interesting for bodybuilders too, as the anti-estrogenic effect of vitamin D is expressed mostly in the fat tissue. What’s more, vitamin D enhances the effect of anti-oestrogens like anastrozole, letrozole and exemestane.

The researchers want to know whether dietary changes can reduce the chance of breast cancer in women and improve treatment chances in women who already have breast cancer. Estradiol often causes breast cancer cells to grow faster. So doctors treat breast cancer with drugs that reduce the concentration of estradiol. The researchers already knew that vitamin D blocks the production of the alpha-estradiol receptor, and wondered whether vitamin D also reduces the production of estradiol itself. That would happen by inhibiting the enzyme aromatase, which converts androstenedione and testosterone into estradiol.

In an article appearing in the Annals of Oncology website titled “Aromatase Inhibitor-Induced Arthralgia – A Review” I found the following helpful information which goes a long way toward explaining how a lack of estrogen caused by AIs could certainly cause suboptimal levels of vitamin D: “ Vitamin D is closely tied to estrogen because estrogen increases the activity of 1-α hydroxylase, the enzyme responsible for conversion of 25OHD to the biologically active 1,25-dihydroxyvitamin D form. Estrogen also increases the activation of the vitamin D receptor. Thus, it seems logical that the drop in estrogen levels caused by AIs may cause a decrease in vitamin D, and thus, a vitamin D deficient-like arthralgia syndrome. “

Another study titled “Non-herbal Nutritional Supplements For Symptoms Relief In Adjuvant Breast Cancer: Creating A Doctor-Patient Dialogue” indicated that vitamin D had been “ shown to be effective in reducing the incidence and severity of arthralgia resulting from treatment with the aromatase inhibitor letrozole. ” No dosages were recommended, however.

A more recent study released in March 2014, “Hypovitaminosis D Is A Predictor Of Aromatase Inhibitor Musculoskeletal Symptoms” appearing in The Breast Journal agreed with the Spanish study, finding that women with vitamin D levels under 40 ng/ml and taking AIs were much more likely to suffer with musculo-skeletal pain, concluding that “ Further research should be carried out on identifying additional modifiable risk factors for this syndrome. “
Yes, indeed. Or maybe we could just get our vitamin D levels checked before starting the aromatase inhibitors and, if they are found to be suboptimal, start supplementing with vitamin D3. The test you want your doctor to perform is 25(OH)D, also referred to as 25-hydroxy-vitamin D.

Dosages will depend upon how deficient you are, but up to 4,000 iu/day have been well tolerated by most healthy people. If you are taking AIs, however, you may be able to tolerate more than that. I would highly recommend seeking the advice of a qualified professional because vitamin D is one of the fat soluble vitamins, meaning that it can accumulate in your body, it isn’t flushed away like excesses of water soluble vitamins such as vitamins B and C.

Not only will the vitamin D most likely assist in the joint pain associated with taking aromatase inhibitors, it just might also reduce risk of recurrence