Vitamin D is not simply one chemical but many. It is also known as calcitriol, ergocalciferol, calcidiol and cholecalciferol.1 The natural type is produced through your skin from a universally present form of cholesterol, 7-dehydrocholesterol. When the term vitamin D is used, it is completely misleading because the truth is, this “vitamin” is not a vitamin it is a ‘Prohormone’.
A Prohormone is a crucial substance that your body converts into hormones.2 Hormones are signaling molecules that govern basic activities of your cells and coordinate multiple-cell actions. 3
Vitamin D is a prohormone that your kidneys produce through a chemical reaction that occurs when sunlight contacts your skin. This reaction produces cholecalciferol, and your liver then converts it to calcidiol. Finally, your kidneys convert that substance into calcitriol, which is the active form of the hormone used in your body for various processes. However, calcidiol is the form that doctors most commonly focus on when measuring the vitamin D levels in your blood.
So, unlike vitamins, only about 10% of the vitamin D your body needs comes from foods you eat while the rest, your body makes itself. Gaining an understanding of this prohormone and the role it plays in your health will help you make more informed health decisions.
How Important is Vitamin D?
Research is currently underway into why this hormone impacts so many systems of your body. Vitamin D is predominantly known to control blood calcium concentration and has been recently recognized as an immunoregulator because it plays such a major role in your immune system.4 It produces these effects by binding to a protein which is aptly called the ‘Vitamin D Receptor’ (VDR).5
This receptor is present in nearly every cell of your body and affects many different body processes. VDRs are present on a large variety of cell types, including neurons, immune cells, myocytes, cardiomyocytes, pancreatic beta-cells, vascular endothelial cells, and osteoblasts. VDR is present in most tissues, including endothelium, vascular smooth muscle, and myocardium. Much more research is needed surrounding vitamin D function in order for us to fully comprehend how it is linked to such a variety of health concerns.
In fact, directly or indirectly, calcitriol (1,25(OH)2D the active form of vitamin D)6 regulates over 200 genes, including those involved in renin production in your kidneys, insulin production in your pancreas, release of cytokines from lymphocytes to keep your immune system functioning, production of cathelicidin in macrophages which clean-up your cellular debris, foreign substances, microbes, cancer cells; and finally in growth and proliferation of both vascular smooth muscle cells and cardiomyocytes for your cardiovascular health.
How is Vitamin D Put into Use by Your Body?
You will not find anything labeled simply as “vitamin D” in your health food store, pharmacy or grocery store vitamin aisle. Instead, your choices will be either vitamin D2 or vitamin D3. Typically, when someone mentions vitamin D, the implied selection is vitamin D3. The strength of both is typically measured in international units, which is abbreviated as “IU” on the labeling. Between the two, vitamin D3 is considered to be superior in producing higher levels of 25D, or calcifediol.
Vitamin D2 (ergocalciferol)7 is less expensive to produce than vitamin D3 and therefore the form most commonly found in fortified food products.8
Vitamin D3 (cholecalciferol)9 is not found in any natural foods except fish and egg yolks, and even when it’s obtained from foods; it still has to be transformed by your body before it will be effective.10 it is sometimes referred to as the ‘sunshine vitamin’. This is because when your skin is exposed to sunlight, it produces vitamin D3. When the sun’s ultraviolet B (UVB) rays make contact with, 7-dehydrocholesterol in your skin cells, this provides the energy for vitamin D3 synthesis to occur.
Vitamin D and Calcium Intake
Vitamin D assists in the absorption of calcium from your small intestine, while also helping to retain calcium that might otherwise be excreted. Additionally, it helps you to maintain healthy phosphorus levels. These main actions happen because calcitriol, the active vitamin D stimulates the active calcium transport through your intestinal wall. When there is adequate vitamin D present, this makes calcium intake easier. Without vitamin D your bones can become soft, thin and brittle. Insufficient vitamin D is also connected to osteoporosis.
Vitamin D and Sports
Vitamin D has demonstrated many skeletal and extra-skeletal health benefits. A strong correlation has been shown between vitamin D sufficiency, and optimal muscle function. Increasing levels of vitamin D were shown to reduce pain, inflammation and myopathy while increasing muscle protein synthesis, ATP concentration, exercise capacity, jump height, jump velocity, jump power, and strength. Research suggests that sufficient circulating levels of calcidiol, positively affect musculoskeletal injury prevention and recovery. 11
Some Causes of Vitamin D Deficiency
Interestingly, your body cannot produce vitamin D3 if you are merely sitting indoors by a sunny window, because the ultraviolet B (UVB) rays (those that your body needs to make vitamin D3) cannot pass through the glass. The same applies to cloudy days. In fact, age, pollution, time of day, latitude, and seasonal changes all affect your cutaneous vitamin D production.
Also, those with higher amounts of melanin in their skin, in other words people with darker skin tones, such as those of African, African-Caribbean or south Asian origin, will need to spend longer in the sun to produce the same amount of vitamin D3 as someone with lighter skin.12
Areas that are far from the tropics, and closer to the poles have lower intensity of UVR, which is reflected in lighter-skinned populations and correspondingly, a greater need for vitamin D3 supplementation. This is due to increased atmospheric filtering of UVB radiation caused by the oblique angles of the sun’s rays at higher latitudes.
It is estimated that in the US, over 75% of whites and 86% of African Americans and 82% Latinos are vitamin D deficient.13 But the problem goes deeper. Vitamin D3 deficiency affects almost 50% of the world’s population. This is an estimated 1 billion people worldwide, across all ethnicities and age groups. Also, vitamin D3 deficiency often remains undiagnosed or undertreated. This pandemic of Hypovitaminosis D is attributed to our modern lifestyle and environmental factors that reduce our natural exposure to sunlight, which is necessary for ultraviolet-B (UVB)-induced vitamin D production in the skin.
Concern has been expressed that the recent widespread use of sunscreen, particularly those with high sun protection factors, may lead to a significant decrease in solar‐induced pre-vitamin D3 in the skin, which results in a vitamin D level decrease. According to one research group from the College of Osteopathic Medicine at Touro University California, using sunscreen with an SPF of 15 or higher can reduce the body’s vitamin D3 production by 99%.14
Another reason for the high deficiencies worldwide may be due to the recommended age-dependent guidelines for adequate intake of vitamin D3 were established before the publication of studies which strongly suggest that 25(OH)D levels of greater than 30 ng/mL are actually needed to ensure parathyroid hormone (PTH) suppression into the normal range.
Worldwide weight increase trends15 present another potential reason for the decline in vitamin D sufficiency. Excess adipose tissue may lead to withholding of vitamin D, making it less available for use in the body.16 Lastly, these deficiencies may exist because physicians may simply be uncomfortable recommending larger doses of vitamin D3.17
Vitamin D Deficiency Concerns
Inflammation is involved in many chronic diseases, and concern has been raised about the influence of vitamin D deficiency on inflammatory processes. When studies revealed a direct association between inflammatory diseases and low serum 25-hydroxyvitamin D (25(OH)D),(18, 19,20,21) further research was prompted and it showed evidence of low vitamin D in a large segment of the general population. This led many authorities to declare a world-wide epidemic of vitamin D deficiency and they recommended vitamin D supplementation.
As an example, too little vitamin D has been shown to make a person more prone to infections and sickness. Vitamin D3 deficiency results in illnesses ranging from metabolic syndrome, obesity, type-2 diabetes, kidney disease, fibromyalgia, chronic fatigue syndrome, bone loss, osteoporosis and neuro-degenerative diseases including Alzheimer’s disease.
Current research indicates vitamin D3 deficiency plays a role in causing 17 varieties of different cancers especially breast, prostate, and colon cancers,22 as well as stroke, autoimmune diseases, birth defects, and periodontal disease. Vitamin D3 is also believed to play a role in increasing neuromuscular function and protecting the brain against toxic chemicals, and potentially reducing pain.
Research has further demonstrated that low vitamin D levels increase an individual’s risk of depression significantly. This is because vitamin D has been found to help regulate adrenaline, noradrenaline (also called norepinephrine), and dopamine production in the brain; and further helps to protect you from serotonin depletion.
When it comes to your cardiovascular health, mounting evidence suggests that cardiovascular disease is associated with vitamin D deficiency.23 There have now been significant associations between low 25(OH)D levels and increased risk of fatal cardiovascular events, in particular, sudden cardiac death. Vitamin D3 deficiency activates what’s called the renin-angiotensin-aldosterone system and can predispose a person to hypertension and left ventricular hypertrophy. Additionally, vitamin D deficiency causes an increase in your parathyroid hormone (PTH), which both increases insulin resistance and is associated with diabetes, hypertension, inflammation, and increased cardiovascular disease risk. In epidemiologic studies an association has been made between low 25-hydroxyvitamin D levels with coronary risk factors and adverse cardiovascular outcomes.24
Supplementing with Vitamin D
Your doctor may determine your vitamin D recommendation based on lab work.