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Soya isoflavones enhance the effect of antidepressants

The isoflavones in soya enhance the effect of medicines that boost the concentration of serotonin in the brain. Researchers at the Universidad Autonoma de Santo Domingo in the Dominican Republic did an experiment with 40 women suffering from mild depression and discovered that a daily dose of several tens of milligrams of soya isoflavones not only boosted the effect of fluoxetine and sertraline, but also itself helped reduce feelings of depression.

Estradiol and depression

Women in the menopause are much more likely to become depressed because their ovaries stop producing estradiol. Estradiol plays a key role in the production of receptors for serotonin, the neurotransmitters that has been coined 'the happiness hormone' by the media. With time the production of serotonin receptors returns, but sometimes the menopause results in clinical depression that requires treatment.

There are countless studies which have shown that synthetic oestrogens can help menopausal women with depression, so the researchers were curious to know whether supplementation with the plant-based oestrogens found in soya would have the same effect whether or not they were combined with SSRIs. SSRIs are a group of antidepressants.

The researchers did trials with 40 women aged between 45 and 55, whom they divided into 4 groups. All women were suffering from depression and were in the menopause. The experiment lasted three months.

Soya isoflavones enhance the effect of antidepressants

One group of women was given a daily 10 mg of fluoxetine, the active ingredient in Prozac. [Structural formula shown above on the right.]

Soya isoflavones enhance the effect of antidepressants

Soya isoflavones enhance the effect of antidepressants
A second group of women was given a daily capsule containing 100 mg soya extract. The researchers used a product manufactured by GNC, which contained 50 mg soya isoflavones per capsule. The isoflavones were sugared. If you disregard the sugar chains each capsule contained only 20 mg pure isoflavones. The most important isoflavone in soya is genistein. [Structural formula shown here.]

A third group took a daily 50 mg of sertraline, the active ingredient in Zoloft. [Structural formula shown above on the left.]

A fourth group took 50 mg sertraline daily, plus a capsule of soya extract.

The researchers used the Hamilton Rating Scale for Depression, a multiple-choice questionnaire that doctors use to measure depression, giving it a numerical score. Scores from 0-7 are normal, scores above 20 are indicative of a depression. At the start of the study the women scored an average age of 19.7.

The figure below shows that the symptoms of depression decreased considerably in the women who only took isoflavones.

Soya isoflavones enhance the effect of antidepressants

Soya isoflavones enhance the effect of antidepressants

Soya isoflavones enhance the effect of antidepressants

Soya isoflavones enhance the effect of antidepressants

The decrease in symptoms of depressions was biggest in the women who had taken sertraline and the soya supplement.

"We conclude that the administration of soybean could enhance the response to SSRI antidepressants in menopausal women, and that soybean could act as an interesting alternative to estrogens in the treatment of mood disorders during menopause", the researchers wrote.

The researchers formulate their conclusions cautiously. Their study was a small one, and there were no placebo groups.

Nevertheless the study is interesting. Would supplements containing L-tryptophan or 5-HTP be more effective mood boosters in combination with isoflavones.

Acta Pol Pharm. 2014 Mar-Apr;71(2):323-7.

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