From Science Daily
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.
To answer this question the researchers did trials with female mice that had had human cancer cell implants. The mice were given 0.1 mg androstenedione daily, and for the three days before the researchers analyzed them they were given a daily injection of 0.75 mg calcitriol as well. [Cal] A control group was given injections containing inactive ingredients. [Veh] The figure below shows that the cancer cells and the fat cells of the Cal mice produced less aromatase.
The figure above shows that in human cells estradiol production declines as the concentration of calcitriol increases. This effect is interesting for bodybuilders. Less estradiol means that fat cells can’t grow so easily and so shrink faster. It also means less risk of gyno. At least, if it’s valid to extrapolate the results of this study to humans.
The researchers also studied the joint effect on the growth of cancer cells of aromatase inhibitors when taken with arimidex, exemestane and letrozole on the one hand and with vitamin D on the other. The researchers grew human cancer cells in test tubes and added testosterone together with aromatase inhibitors and vitamin D. The figure below shows that vitamin D enhances the effect of arimidex, and the figures for exemestane and letrozole were pretty similar.
The researchers used 0.1 and 1.0 nanomol concentrations of calcitriol. Concentrations of calcitriol in humans vary between 0.05 and 0.16 nmol. Because westerners in general have too little vitamin D in their blood, many chemical bodybuilders will derive more effect from the aromatase inhibitors they take by adding a supplement that contains extra vitamin D.
But estradiol is good for bones. Women who use aromatase inhibitors often have problems with osteoporosis, and chemical athletes also report bone and joint problems from taking high doses of anti-oestrogens. However, the researchers also discovered that vitamin D increases the production of aromatase and estradiol in the bones.
Endocrinology. 2010 Jan; 151(1): 32-42.