Prostate cancer hangs like the sword of Damocles over the heads of all men. Those who live long enough are likely to develop the disease and this is one reason for the growing interest in dietary habits that may reduce the chance of getting prostate cancer. Back in 2002 researchers at Wake Forest University published the results of a test-tube study which suggested that a diet containing soya protein and vitamin D might protect men against this form of cancer.
Animal studies have shown that vitamin D supplementation inhibits the growth of the prostate as a result of androgens. [J Cell Biochem. 2003 Sep 1;90(1):138-47.] Epidemiological and in-vitro studies have shown that soya-based protein-rich foods inhibit the growth of prostate cancer cells. [Exp Biol Med (Maywood). 2010 Jan; 235(1): 90-7.] [Food Chem. 2012 Dec 1; 135(3): 1643-52.] The active substances in soya are probably isoflavones like genistein.
So what would happen if you exposed prostate cancer cells simultaneously to isoflavones and vitamin D? This is the question that the researchers at Wake Forest University set out to answer with their experiments. The figures below summarise the results. Click on them to obtain larger versions.
WFU55PZ- and WFU58PZ-cells are benign cells from the epithelium of a human prostate gland. LNCaP-cells are androgen-sensitive prostate cancer cells. The combination of vitamin D and genistein helped decimate both kinds of cell types.
The figure above shows that the combination inhibits the cell cycle. G0: cell resting and not dividing; G1: cell growing and preparing to make new DNA; S: cell producing new DNA; G2: cell preparing to divide and growing more; M: cell divides into two new cells.
Researchers at Stanford University have a theory about the way in which isoflavones and vitamin D reinforce each other's effect, and this is summarised in the figure below. [J Nutr. 2007 Jan; 137(1 Suppl): 205S-210S.]
Isoflavones inhibit the enzyme 25-hydroxyvitamin D-24-hydroxylase or CYP24A1. CYP24A1 breaks down the active form of vitamin D, so isoflavones help increase the concentration of vitamin D. At the same time isoflavones inhibit the effects of the inflammatory factors PGE2 and PGF-2alpha, which help cancer cells to grow faster.
The Stanford University researchers published a few months ago the results of an animal study in which they implanted human prostate cancer cells in mice. [Prostate. 2012 Nov; 72(15): 1628-37.] They then gave the animals an injection of calcitriol [the active form of vitamin D3] and food containing soya protein. The figure above is taken from the study.
The researchers discovered that the combination of soya and calcitriol results in a rise in calcium levels and a dramatic rise in the amount of calcitriol; so high that some of the lab animals died. That only happened to the mice that had been given a diet of which 20 percent of the energy was derived from soya. Although the calcitriol injections contained far higher quantities than oral vitamin D3 supplements do, the researchers warn doctors who may be thinking of experimenting with soya and vitamin D3 combinations: excessive quantities can damage your health.
J Nutr. 2002 Oct;132(10):3191-4.