Vitamin D deficiency and low testosterone concentrations in men can affect their fertility or lead to osteoporosis and loss of muscle mass. New Danish research shows that these two factors may be more closely related than previously thought, since vitamin D deficiency may reduce testosterone production.
We get vitamin D from sunlight exposure, food and dietary supplements. The concentration of vitamin D in the blood may affect men’s testosterone production.
For most men, a higher vitamin D intake will probably not strongly influence the concentration of testosterone, but men with vitamin D deficiency might consider vitamin D supplements to boost the concentration of testosterone in the body and perhaps also fertility.
This is the conclusion of a new Danish study in which researchers linked the concentration of vitamin D in the blood and the body’s production of testosterone.
“We have been researching how vitamin D affects reproduction for many years. What is new about this study, is that we can show that vitamin D influences testosterone production. There appears to be a direct link, and one may speculate whether supplementation of vitamin D for vitamin D–deficient men may give a clinically relevant increase in testosterone,” says Martin Blomberg Jensen, doctor and Group Leader, Group of Skeletal, Mineral and Gonadal Endocrinology, Department of Growth and Reproduction, Rigshospitalet, Copenhagen.
The study was recently published in the Journal of Steroid Biochemistry and Molecular Biology.
Testosterone is important for fertility and health
Testosterone is produced in men’s testicles and is strictly regulated by the pituitary hormone luteinizing hormone (LH).
The pituitary gland is sensitive to the concentration of sex hormones in the blood, and when the concentration drops, the pituitary gland secretes LH, which is the main stimulator of testosterone production.
Men who only have one testicle typically need a higher concentration of LH to achieve sufficient concentrations of testosterone, since the remaining testicle has to perform the entire task and therefore needs additional stimulation.
Lower testosterone production can result in less energy, less muscle mass, reduced sexual desire and increased risk of osteoporosis.
In addition, infertile men produce less testosterone than men with normal fertility.
Observational study of Danish men
In the new study, researchers from Rigshospitalet investigated whether they could find an association between the blood concentrations of vitamin D and testosterone among two groups of Danish men.
One group comprised 41 men who had a testicle removed because of testicular cancer and the other group comprised 300 healthy young men.
The researchers took blood samples from all the men and determined the concentrations of testosterone, LH, vitamin D and the calcium-regulating hormone parathyroid hormone.
Correlating parathyroid hormone and vitamin D provides researchers with a more nuanced view of an individual’s vitamin D status than the vitamin D concentration alone, while testosterone and LH reveal the state of the pituitary gland and testicular function.
“The relationship between testosterone and LH indicates how much testosterone the testicles can produce compared with the amount of LH,” explains the first author, Rune Holt, doctor and PhD student.
Vitamin D deficiency leads to reduced production of testosterone
The results of the study showed that the blood concentrations of testosterone and vitamin D were linked among the 300 healthy men with normal testosterone production.
Healthy men with low vitamin D and high parathyroid hormone concentrations, had a lower ratio of testosterone to LH in the blood suggesting that the effect of LH on testosterone production may be reduced when vitamin D is low
Forty-one men who had one testicle removed received an injection of human chorionic gonadotropin to test the ability of the remaining testicle to produce sufficient testosterone.
The researchers simultaneously determined the men’s blood concentration of vitamin D and found that men with low vitamin D levels reacted less positively to the injection of human chorionic gonadotropin than men with normal or high vitamin D concentrations.
Martin Blomberg Jensen explains that this discovery is clinically relevant.
“Men who have had one testicle removed often undergo a hormone stimulation test using human chorionic gonadotropin to test whether the remaining testicle is capable of producing sufficient testosterone. Our results indicate that examining these men’s vitamin D concentrations before examining their testicular function may be clinically relevant, since it may affect how well they respond to human chorionic gonadotropin stimulation,” says Martin Blomberg Jensen.
Vitamin D supplements might have a doubly positive effect on bone health, since vitamin D deficiency is associated with an increased risk of osteoporosis as is testosterone deficiency.
Vitamin D supplementation to ensure higher testosterone concentrations can therefore have additional positive health effects.
Infertile men with vitamin D deficiency should take vitamin D
The researchers also investigated whether vitamin D can directly stimulate testicular tissue to produce testosterone.
The testicular tissue came from men who had one testicle removed because of testicular cancer. After the operation, the researchers extracted some healthy testicular tissue that did not contain cancer cells and cultured it in the laboratory.
The researchers applied activated vitamin D to the tissue and then monitored the secretion of testosterone.
The tissue exposed to activated vitamin D produced more testosterone than the tissue that did not get vitamin D.
This indicates that vitamin D affects testosterone production directly in the testicles.
“We are now awaiting data from a large study in which we have given infertile men with vitamin D deficiency high doses of vitamin D to determine whether this can increase their testosterone production and improve their fertility,” explains Martin Blomberg Jensen.
Martin Blomberg Jensen expects the results of this new study to emerge in 2020, and although he cannot yet reveal the results, there is reason for optimism: men with reduced sperm production have become more fertile after treatment with vitamin D versus placebo-treated men.
“Vitamin D and sex steroid production in men with normal or impaired Leydig cell function” has been published in the Journal of Steroid Biochemistry and Molecular Biology. The Novo Nordisk Foundation awarded grants to Martin Blomberg Jensen for the project Clinical Relevance of the Calcium-sensing Receptor in Reproduction in 2018 and for the project RANKL and Male Fertility, an Excellence Project for Young Researchers within Endocrinology and Metabolism, in 2017.