Selenium supplements and breast cancer

Studies show that selenium intake and status are associated with breast cancer risk.  Low selenium status indicates an increased risk of breast cancer.

In many countries, breast cancer is the most commonly diagnosed and treated form of cancer.  A 2014 meta-analysis of 16 studies has shown that there is a statistically significant association between serum selenium status and risk of breast cancer.  The lower the serum selenium concentration, the greater the risk of breast cancer [Babaknejad].

What do we know about selenium and breast cancer?
Breast cancer is a frustrating topic for the selenium researcher.  There is not enough evidence to permit definitive statements about the effects of selenium supplementation on the prevention of breast cancer.

For example, the Nutritional Prevention of Cancer (NPC) study – a study that showed significant associations between selenium supplementation and reduced risk of colorectal, lung, prostate, and total cancer – did not enroll enough women for the effect of selenium supplementation on breast cancer to be studied [Clark].

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Selenium helps to avoid pregnancy complications

Adequate intakes of selenium can help to reduce the risk of some of the more serious complications of pregnancy. Studies done with an organic high-selenium yeast supplement have yielded encouraging results.

Women who have first-trimester miscarriages or recurrent miscarriages have been found to have significantly lower selenium status than women who do not miscarry.  Professor Margaret Rayman points out that blood selenium concentrations are typically lower during pregnancy, in part because there is an expansion of the volume of blood.  However, increased inflammation – implicated in miscarriages – could also be a cause of reduced circulating selenium [Rayman 2012].

For this article, I have searched the Medline database for results from randomized controlled studies involving selenium supplementation of low selenium status pregnant women.  There have been a number of interesting results.

Selenium and oxidative stress in pregnant women
Dr. Tara and a team of researchers did a simultaneous assay of pro-oxidant burden and antioxidant capacity in a total of 166 first-time-pregnant women.  In their first trimester, the women were randomly assigned to an active treatment group receiving 100 micrograms of a yeast-based selenium preparation (n=83) or placebo (n=83) per day until delivery.

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Selenium and heavy metals and childbirth

Studies show that higher concentrations of dangerous heavy metals — cadmium, mercury, and lead — in the blood of the mother are likely to be duplicated in the umbilical cord blood, in the blood of the fetus, in the breast milk, and in the blood of the newborn child, with potentially harmful long-term consequences for the child. There is evidence that selenium binds with cadmium and mercury and enables their elimination from the mothers’ bodies.

Early exposure to natural elements that are toxic – cadmium, mercury, and lead – can have long-term adverse health consequences.  Children exposed to these elements while still in the uterus and while breast-feeding may suffer lasting damage to the brain and nervous system and to the kidneys and liver.  The question is: to what extent can selenium supplementation reduce the risk of toxic damage?

Given the dangerous nature of these poisonous heavy metals – cadmium, mercury, and lead – both for the mother and for the fetus and the neonate, it is difficult to carry out randomized controlled studies.  Instead, the best evidence we have for the beneficial effects of selenium supplementation comes from studies that relate the degree of exposure and the selenium status of the mother and the child.

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