Fifteen men (mean age, 61.5 years) recently diagnosed with prostatic intraepithelial neoplasia (PIN) and/or atypia, who were scheduled for a repeat biopsy after six months, consumed a low-fat diet (< 20% of energy) supplemented with 30 g/day (approximately 3 tablespoons/day) of ground flaxseeds. After six months, a statistically significant decrease in the mean level of prostate-specific antigen (PSA; 5.72 vs. 8.47 ng/ml; 32.5% reduction; p = 0.0002) was seen. The mean serum testosterone concentration did not change significantly. Repeat biopsy was not performed in 2 patients because the PSA level had become normal. Among the 13 men who underwent repeat biopsy, the mean proliferation rate in the benign epithelium decreased significantly by 68% at six months (p = 0.0168). The clinical pathology reports indicated PIN and/or atypia in all cases at baseline; however, when re-reviewed by the reference pathologist, only 7 of 15 patients had PIN and/or atypia at baseline, and 1 of 13 at follow-up.
Comment: The results of this study suggest that supplementation with flaxseeds, when used in conjunction with a low-fat diet, can reduce the proliferation rate of benign prostatic tissue, and may also reverse precancerous changes in prostate tissue. Eating ground flaxseeds may, therefore, be helpful for preventing the development or progression of benign prostatic hyperplasia (BPH) and may also help prevent prostate cancer. These effects may be due to the lignans in flaxseeds, which can reduce testosterone levels and inhibit the conversion of testosterone to dihydrotestosterone.
Several recent epidemiological studies have shown an association between increasing intake of alpha-linolenic acid (ALA) and increased risk of prostate cancer. As flaxseed oil is one of the most potent sources of ALA, some physicians are now reluctant to prescribe flaxseed oil for men, despite anecdotal reports of its value as a treatment for BPH. Whether or not these epidemiological studies reflect cause-and-effect or whether the findings are due to unidentified confounding factors is not known. The results of the present study, however, suggest that ingestion of ground flaxseeds is beneficial, not harmful, to the prostate. The lignans in flaxseeds tend to be concentrated in the non-fat portion, as opposed to oil; even so-called "high-lignan" flaxseed oil does not appear to contain a large amount of lignans. Until further information is available, ground flaxseeds may be considered as potentially safer and more beneficial than flaxseed oil.
One potential negative effect of consuming flaxseeds is the development of vitamin B6 deficiency. Flaxseeds contain a substance called linatine, which interferes with the utilization of vitamin B6. Pigs fed a diet containing 30% by weight of flaxseed had impaired growth and laboratory evidence of vitamin B6 deficiency. Although the effect of eating smaller amounts of flaxseed on vitamin B6 status has not been investigated, it would be prudent for people who habitually consume flaxseed to take a multivitamin that contains vitamin B6.
Demark-Wahnefried W, et al. Pilot study to explore effects of low-fat, flaxseed-supplemented diet on proliferation of benign prostatic epithelium and prostate-specific antigen. Urology 2004;63:900-904.
