Selenium is a trace element that supports over 30 essential selenoproteins, which have numerous functions. For the first time ever, a study of Mexican children reveals that lack of selenium delays the growth of pubic hairs and the development of sex organs in boys. It is a known fact that the agricultural soil in Mexico is low in selenium and that affects the entire food chain. The same is the case in Europe, for which reason farmers for decades have supplemented livestock with selenium as a way of improving fertility and preventing a number of deficiency problems. The big question is to what extent can selenium deficiency problems explain the impaired sperm quality that has been observed among young men? An estimated 500 million to one billon people worldwide get too little selenium from their diet.
Puberty is the period in life where hormones change a child into an adult that is able to reproduce. The puberty is initiated by hormone signals from the brain to the gonads (ovaries or testicles) that make hormones from the gonads stimulate the growth, function, and transformation of the brain, the bones, the muscles, the breasts, and the sex organs.
Over the past decades, science has observed how the onset of puberty has changed and starts earlier. Hormone-disrupting substances are suspected of being the reason why girls today start menstruating earlier, and that hormone-induced cancer forms such as breast cancer and prostate cancer have become increasingly common.
It turns out that our childhood diet accounts for 25% of the variations with relation to the onset of puberty, and scientists have therefore wanted to look closer at selenium’s role.
Selenium’s role in puberty, fertility, and health
Selenium is an essential trace element that plays a vital role in human and animal health. Selenium supports over 30 different selenium-dependent proteins that are important for the thyroid gland, the immune defense, and fertility. Several selenoproteins also function as important antioxidants that protect cells and tissue against oxidative stress caused by free radicals.
Human studies show that lack of selenium may play a role in the development of different cancer forms and that supplementation with selenium yeast may have a preventative effect.
Animal studies have demonstrated that selenium deficiency may cause fertility problems. In humans, low dietary selenium intake may cause male infertility by impairing sperm cell quality and motility, both of which are determining for successful fertilization of the egg. On the other hand, one of the largest studies of infertile men showed that selenium supplementation increases testosterone levels.
Science knows that selenium supplementation of animals improves their fertility rates, and that is why farmers for decades have fed extra selenium to livestock. Still, there have not been studies of how selenium deficiency affects the progression of puberty.
Although selenium’s mechanisms of action remain somewhat unclear, it is quite likely that insufficient selenium intake may affect the body’s development during puberty by interrupting the production of puberty-related hormones and levels of body fat or by promoting oxidative stress.
So far, no epidemiological studies have looked at the relation between selenium levels and puberty, so the whole purpose with the new Mexican study was to investigate how selenium affects young Mexicans’ puberty.
Selenium deficiency delays puberty, decreases pubic hair growth and reduces testicle size
The Mexican study included 274 girls and 245 boys aged 10-18 years from Mexico City. Using a special model, the scientists assessed the relation between diet habits and selenium intake. To determine puberty status, the scientists noted when the girls had their first menstruation, they looked at the development of pubic hair in both sexes, and they looked at the development of the boys’ testicles. It turned out that the majority of children were selenium-deficient. 217 of the girls and 197 of the boys had a selenium intake that was below the official American guidelines, which recommend 40 micrograms for children in the age group 9-13 years and 55 micrograms for anyone from 14 years and older.
The scientists observed that low selenium intake was associated with delayed puberty in boys after adjusting for BMI, number of siblings at birth, age of the mother, marital status, smoking etc. The boys that got too little selenium had less pubic hair, and their testicle volume was smaller than that of boys with sufficient selenium intake. It is commonly known that the growth of pubic hair is highly dependent on androgens (male sex hormones), which are also important for the development of the skeleton and muscle mass. There is also proof that selenium can affect body composition by lowering BMI, waist circumference, and the fat percentage in adults.
Various data failed to show a link between the selenium intake among girls and their development during puberty. However, girls should in any case make sure to get enough selenium because it is important for their metabolism and many other functions, including normal, healthy pregnancy. The study is published in the scientific journal Nutrients.
The scientists looked at earlier studies
Previous research has shown that selenium supplementation can increase levels of insulin-like growth factor 1 (IGF-1), which promotes development during puberty by increasing serum testosterone levels, levels of pituitary hormone, and testicle size in male animals
A clinical study of 443 older Swedish people showed that levels of IGF-1 increased in those participants that took selenium supplements in contrast to those who got placebo. Although the exact mechanisms are still unknown, it is possible that lack of selenium and impaired IGF-1 production is linked to inflammatory processes and oxidative stress. This may contribute to delayed development of male sex organs during puberty.
Earlier studies of male animals show that selenium supplementation improves their fertility. During puberty, levels of selenium in the testicles increase substantially, and if there is a lack of selenium, the brain and testicles compete over the scarce supply of this important mineral.
Studies of sheep show that the sheep mother’s selenium status affects the weight of the uterus and ovaries in female offspring. Similar studies have not been made in humans.
The Mexican study and its conclusion
Based on the outcome of the Mexican study of children and adolescents, the scientists conclude that lack of dietary selenium is associated with delayed growth of pubic hair, delayed development of sex organs, and decreased testicle size in Mexican boys. No correlation was observed between selenium deficiency and development during puberty among Mexican girls. Still, girls should make sure to get enough selenium for many other reasons. The study is the first of its kind among humans to show a link between selenium and development during puberty.
Why is selenium deficiency so widespread?
Like other minerals, selenium is found in the soil. The selenium concentration in soil determines how much the plants absorb and selenium levels in plants affet the entire food chain. Brazil nuts, seeds, grains, green vegetables and shiitake mushrooms are good selenium sources, provided they have grown in selenium-rich soil. There is also selenium in egg yolks, organ meat, and seafood.
Selenium deficiencies typically occur in parts of the world that have low selenium content in the soil.
Yun Liu et al. Dietary Intake of selenium in Relation to Pubertal Development in Mexican Children. Nutrients 2019
Aparna Shreenath. Selenium Deficiency. StatPearls. May 6, 2019
Aparna P. Shreenath; Jennifer Dooley. Selenium, Deficiency. NCBI October 27, 2018
Annette Hagerup. Puberteten kommer et år tidligere. Sygeplejersken 2009
Hilten T Mistry et al. Selenium in reproductive health. Journal of Obstetrics and Gynaecology. 2011
Fatemeh Tara et al. Selenium Supplementation and the Incidence of Preeclampsia in Pregnant Iranian Women: A Randomized, Double-Blind, Placebo-Controlled Pilot Trial. Taiwanese Journal of Obstetrics and Gynecology. 2010
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