Vitamin D – The Importance of One Micronutrient

vitamin d, healthy man

Vitamin D is the sunshine vitamin that is so much more than a daily dietary requirement.

This essential micronutrient, obtained through sun exposure, certain foods, and supplements, serves as the powerhouse behind many bodily functions.

From enhancing testosterone production to maintaining bone and heart health, boosting immunity, regulating mood, and improving muscle strength, vitamin D wears many hats. Yet, striking the balance for adequate intake is a challenge for many.

Read on to uncover the numerous effects of this vitamin and understand why it’s a vital part of your health journey.


  • Vitamin D is a micronutrient, essential to humans
  • It can be obtained from sunlight, food, or dietary supplements
  • It has numerous beneficial effects:
    • Testosterone Production
    • Bone Health
    • Immune Function
    • Mood and Mental Health
    • Heart Health
    • Muscle Strength and Function
  • Multiple studies have shown that vitamin D increases testosterone production, vital for men’s health
  • It does this by:
    • Boosting testosterone production in leydig cells
    • Reduces Sex Hormone-Binding Globulin (SHBG)

What is Vitamin D?

Vitamin D, how much vitamin D, men's health

Vitamin D is a fat-soluble micronutrient that is essential for various physiological processes in the body.

There are two major types:

  • Vitamin D2 (ergocalciferol), which is commonly found in plants
  • Vitamin D3 (cholecalciferol), which is synthesized in the skin when exposed to sunlight and can also be found in animal products.

These two forms of vitamin D are biologically inactive, and must undergo two hydroxylation processes in the body for activation; the first in the liver and the second in the kidneys. The resulting compound, calcitriol, is the active form of vitamin D.

How Much Vitamin D Do We Need?

The Institute of Medicine, Food and Nutrition Board define the Recommended Dietary Allowance (RDA) of vitamin D as 600iu per day for men. As the RDA is the daily intake of a nutrient considered sufficient to meet the requirements of 97.5% of healthy individuals, any daily vitamin intake values below 600iu pose increased risks to health for 97.5% of people.

One study considering the levels of vitamin D in the UK population found that roughly 60% of adolescents, adults and the elderly have insufficient levels of zinc, and therefore higher risk to various adverse health effects.

Where Do We Get it?


sunlight, vitamin d

The primary natural source of vitamin D is sunlight exposure. When the skin is exposed to UVB radiation from direct sunlight, a form of vitamin D called cholecalciferol (vitamin D3) is synthesized in the body.

However, the ability to produce enough vitamin D from sunlight depends on factors like geography, season, time of day, age, skin pigmentation, and sunscreen use. In countries where the sun is not always shining and days are shorter, getting enough vitamin D from sunlight becomes particularly difficult.

Melanin is a substance in your body that produces hair, eye, and skin pigmentation. People with higher melanin levels, and therefore dark skin, produce less vitamin D per unit of sunlight received, and therefore people with lighter skin generally produce more vitamin D when exposed to the same amount of sunlight as those with dark skin.

People should be cautious with excessive sunlight exposure though. Too much sunlight can lead to an increased risk of skin cancer, and should therefore care should be taken to avoid excessive sun exposure.


Vitamin D can also be obtained through a healthy diet. Dietary sources of vitamin D include these foods:

  • Fatty fish and fish liver oil
  • Fortified dairy
  • Plant-based milk products
  • Fortified cereals
  • Egg yolks

Vitamin D Supplements

While these sources can give us adequate levels of vitamin D, it can be challenging to obtain sufficient amounts consistently, particularly for individuals with limited sun exposure or specific dietary restrictions.

As mentioned previously, a substantial portion of the population finds it difficult to get enough vitamin D on a consistent basis.

As a result of this, vitamin D supplements can play a crucial role in ensuring people get adequate amounts. Supplements are typically in the form of Vitamin D3, and in doses high enough, can rectify vitamin D deficiency and improve numerous aspects of people’s health.

Vitamin D Benefits

Vitamin D is essential for healthy function of our bodies. It has a number of key beneficial effects, including avoiding and helping significant health problems. Key effects are summarised below.

Testosterone Production and Efficacy

vitamin d, healthy man

Vitamin D levels have been shown to have a positive correlation with testosterone levels and efficacy in men, vital for men’s health. Research has demonstrated that sufficient levels support healthy testosterone production, and this is particularly helpful for individuals experiencing symptoms of testosterone deficiency.

It does this through enhances the function of leydig cells and reducing Sex Hormone-Binding Globulin (SHBG) levels.

Bone Health

Vitamin D plays a crucial role in regulating calcium and phosphorus levels in the body, which are essential nutrients for maintaining healthy bones and bone strength.

It aids in the absorption of calcium from the intestine and helps deposit calcium in bones, promoting their strength and density.

The mechanism by which vitamin D improves bone health is through its interaction with parathyroid hormone (PTH). PTH stimulates the release of calcium from bones into the bloodstream. vitamin D, on the other hand, suppresses PTH production when blood calcium levels are sufficient, to prevent excessive calcium loss from bones.

In addition to this, vitamin D enhances the absorption of dietary calcium in the intestine, making further improvements to bone health and helping to avoid/reduce bone deformities.

Immune Function

vitamin d3

Vitamin D supports the immune system and helps defend against infections and disease. It enhances the function of immune cells, including T-cells and macrophages, which are crucial for fighting off pathogens.

When pathogens invade the body, vitamin D promotes the production of antimicrobial peptides, which are substances that help destroy bacteria, viruses, and fungi. These peptides work by disrupting the cell membranes of pathogens, rendering them ineffective.

Moreover, vitamin D enhances the ability of immune cells to recognize and destroy pathogens, thus bolstering the overall immune response to disease.

Mood and Mental Health

Vitamin D plays a role in brain function and mood regulation. Low levels have been linked to an increased risk of depression, Seasonal Affective Disorder (SAD), and other mood disorders.

One way in which it affects mood is through its influence on serotonin production. Serotonin is a neurotransmitter associated with feelings of happiness and well-being, and vitamin D helps convert the amino acid tryptophan into serotonin, thereby supporting positive mood.

Additionally, vitamin D receptors are present in areas of the brain involved in mood regulation, further highlighting its importance in mental health and depression.

Heart Health

heart health, vitamin d

Research suggests that vitamin D may have cardiovascular benefits. It helps regulate blood pressure, reduces inflammation, improves endothelial function, supports overall heart health, and reduces the risk of heart disease, heart attacks, and stroke.

The protective effects of vitamin D on the cardiovascular system are multifaceted. It helps regulate blood pressure by influencing the renin-angiotensin-aldosterone system, a hormone system involved in blood pressure control. It also reduces inflammation, which plays a significant role in the development of cardiovascular diseases.

Furthermore, vitamin D promotes the production of nitric oxide, a molecule that improves endothelial function (a thin layer cells on the interior of blood vessels) and blood flow, contributing to heart health.

Muscle Strength and Function

Vitamin D is important for maintaining optimal muscle strength and function. It aids in muscle contraction and helps improve muscle performance. As such, vitamin D supplements can improve overall muscle strength.

Vitamin D exerts its effects on muscle strength and function through various mechanisms. It enhances the synthesis of proteins involved in muscle contraction, thereby improving muscle performance.

Additionally, vitamin D helps regulate calcium levels in muscle cells, which is essential for proper muscle contraction. By ensuring adequate levels, individuals can optimize their muscle strength and improve overall physical performance.

Testosterone Levels

What Effect Does Vitamin D Have on Testosterone?

Vitamin D has been shown several times to increase levels of testosterone in men, particularly in men with low testosterone levels. Some key studies and their findings are summarised below.

  • One study found that total and free testosterone was linearly related to vitamin D levels, with individuals who had higher vitamin D levels also having higher total and free testosterone levels.
  • Another study found that vitamin D and free androgens were correlated with vitamin D levels in patients. Testosterone levels were proven to be seasonal in subjects observed, which was presumed to be due to the differing levels of sunlight through the year.
  • One other study gave vitamin D supplements to men with vitamin D deficiency (9.09 – 55.28 nmol/l) for one year. After one year of vitamin D supplementation:
    • Free testosterone increased by 20.27%
    • Bio active testosterone (free + albumin-bound testosterone) increased by 19.96%
    • Total testosterone increased by 25.23%
free testosterone, vitamin d, vitamin d supplements
bioactive testosterone levels, vitamin d supplements, sexual function
total testosterone, low testosterone levels, dietary supplements

How Does Vitamin D Effect Testosterone?

The mechanisms in which vitamin D and vitamin D supplements increase testosterone levels in men are outlined in the following sections. Each is related to Hypothalamic-Pituitary-Gonadal (HPG) axis, which is responsible for producing, regulating, and distributing testosterone.

Increased Leydig Cell Functionality

Leydig cells are located in men’s testes and responsible for the production of testosterone. When they receive a signal from the pituitary gland in the brain, in the form of luteinizing hormone, they begin converting cholesterol into testosterone. As a result, leydig cells’ functionality is critical to testosterone production.

Vitamin D facilitates proper leydig cell function.

Leydig cells have vitamin D receptors in them, allowing for vitamin D to bind to them and facilitate testosterone production when stimulated by luteinizing hormone.

One study investigated the effect of vitamin D in the cells in men’s Testes. It found that:

  • Providing leydig cells with vitamin D showed significantly higher levels of testosterone production than the control group.
  • Providing leydig cells with vitamin D, luteinizing hormone, and Insulin-like Growth Factor 1 (IGF-1), produced significantly higher levels of testosterone when compared to providing them solely with luteinizing hormone or IGF-1.
Reduced Sex Hormone-Binding Globulin (SHBG)

Sex Hormone-Binding Globulin (SHBG) binds to circulating testosterone and reduces how bioactive it is. The majority of testosterone produced by the testes is bound to it. By reducing the amount of SHBG in the body, less testosterone binds to it, and therefore more bioavailable and potent testosterone is free to act cross the body.

Vitamin D has been shown to reduce SHBG levels.

One study investigating the effect of vitamin D on testosterone and SHBG found that higher vitamin D levels were linked to low SHBG levels and high testosterone, and low levels were linked to higher SHBG and low testosterone. Therefore indicating that sufficient levels of vitamin D aid in not only the production of testosterone, but also its efficacy.


vitamin d

In summary, vitamin D is a fat-soluble micronutrient, sourced from sunlight exposure, diet, and supplements, essential for various physiological functions in the body.

The micronutrient plays a crucial role in testosterone production, bone health, immune function, mood regulation, heart health, and muscle function. It works by boosting testosterone production in leydig cells and reducing Sex Hormone-Binding Globulin (SHBG) to increase bioactive testosterone.

It also regulates calcium and phosphorus levels for bone health, enhances immune cell function, influences serotonin production for mental health, and improves muscle function and performance.

However, a significant portion of the population struggles with maintaining sufficient vitamin D levels, pointing to the importance of supplements for promoting overall health.

At StayPrime, we use vitamin D in our ZMAN+ supplement formula to enhance overall our customers overall wellbeing. Incorporate it into your daily routine to maintain your prime.



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