Vitamin D: Aromatase Inhibitor

I know what you’re thinking – “Another article on vitamin D?!” Well, yes. Yes it is. And honestly, expect many more as the amount of research coming out on this wonder-compound is pretty vast. In today’s installment I’ll be discussing vitamin D and its effect on estrogen metabolism.

While most of you will already have quite an extensive knowledge of what aromatase is and what it does, for those that don’t here is your crash course. Aromatase is an enzyme that increases the amount of estrogens in the body by converting androstenedione (“andro”) to estrone and testosterone to estradiol. There, that wasn’t too bad now was it.

Researchers at Stanford’s School of Medicine wanted to see what vitamin D’s active form, calcitriol, would do regarding breast cancer. What they found was that calcitriol reduced aromatase expression in two ways – firstly, by directly suppressing its transcription at the gene level i.e. reducing how much of it is produced by the body. And secondly, by suppressing Cyclooxygenase-2 (COX-2), a pro-inflammatory pathway, and increasing 15-Hydroxyprostaglandin Dehydrogenase (15-PGDH), an anti-inflammatory pathway. Combined, this effect reduces the levels of local prostaglandins including Prostaglandin E2 (PGE2), which is a major stimulator of aromatase transcription. They also found that calcitriol downregulates the expression of estrogen receptor alpha (ERa) in breast cancer cells, therefore reducing the effects of estrogen signalling at the receptor level.

Unlike prescription aromatase inhibitors, this is a much more targeted route for this purpose with calcitriol being selective for which cells it has this effect. That is really cool as it means that it doesn’t have same estrogen-leeching effect on bone that some Rx aromatase inhibitors have which can cause problems. This is evident in women who have gone through the menopause and have brittle bones due to osteoporosis.

One last thing of note for those of you taking large doses of supplemental vitamin D3: those of you that tuned into Superhuman Radio last week will have heard me discuss Vitamin D with the show’s host Carl Lanore. You will have also made note that you need to be careful with your dose as this is a fat soluble vitamin that can interfere with vitamin A in the liver. For those of you who live in sunny climates year-round and actually get outside a lot, you probably do not need to supplement with any D3. Those who have dark winters absolutely should, but remember to taper your dosing over the summer months when you are getting plenty of sunshine. Some of the more intelligent folk who take D3 regularly do so on a five days on–two days off approach. I really like this scheme.

Check out Super Human Radio episode: 475 and 482 for more on this topic and others!

Source: Krishnan AV, Swami S, Feldman D. Vitamin D and breast cancer: Inhibition of estrogen synthesis and signaling. J Steroid Biochem Mol Biol. 2010 Feb 13.