The Sunshine Vitamin: Unlocking the Power of Vitamin D

“The interplay between vitamin D, calcium, phosphorous and bones is integral for maintaining strong and resilient skeletal structures”.

Prologue	Science	Benefits	Dosage
Sources	Recommendations

The Power of Vitamin D

Vitamin D holds a special place as an essential nutrient required by humans for their optimum development and maintaining overall health and well-being^[1,2]. Commonly known as the sunshine vitamin, it plays a fundamental role in various bodily functions, impacting not only bone health but also influencing our immune system, mood, and overall well-being^[3,4,5,6,7]. Understanding the different aspects tied to vitamin D is essential for assessing nutritional status, optimizing intake strategies, and comprehending the diverse physiological functions of this vital vitamin. In the following sections, we will discuss some important aspects of Vitamin D.

Science of Vitamin D

Vitamin D is a group of fat-soluble steroid compounds which are commonly known as calciferols^[8]. It exists in two main forms i.e., Vitamin D2 and D3^[1,9]. Vitamin D2 is known as ergocalciferol and is found in some plants, mushrooms, and fungi. The more potent and bioavailable form is Vitamin D3 or cholecalciferol. It is primarily derived from sunlight exposure and animal sources^[1,10].

Although vitamin D2 and D3 differ in their structure, it does not result in a difference in their function. When activated, both forms function as prohormones (precursors of hormones) and were reported to exhibit identical functions in the human body^[2].

Although vitamin D can be obtained from certain foods, the most significant and major source of vitamin D for humans is exposure of skin to sunlight^[1,11,12]. Provitamin D3 (7-dehydrocholesterol ) exists in the skin. When ultraviolet B (UVB) rays from the sun make contact with the skin, provitamin D3 is converted into previtamin D3–a precursor of physiologically active form of vitamin D^[2,13].

Vitamin D, in either the D2 or D3 form, is considered biologically inactive^[2]. After synthesis in the skin after UVB exposure or through dietary intake, the previtamins undergo processing, first in the liver (as calcidiol) and later in kidneys to form active vitamin D (calcitriol)^[1,14,15]. Calcidiol is the major circulating form of vitamin D in human serum^[12,16].

The absorption and deposition of vitamin D primarily occurs in the small intestine and various tissues in the body. Vitamin D being fat-soluble, its absorption is closely linked to dietary fat absorption^[17]. The primary storage sites for vitamin D are adipose (fat) tissue and liver^[18]. The stored vitamin D can be released into the bloodstream when there is a need for its active form, calcitriol, to regulate calcium and phosphorus metabolism^[19].

Health Benefits of Vitamin D

Calcium, Phosphorus absorption and Bone Health

Vitamin D is a special type of nutrient because in its active form it is a hormone^[2]. Calcium and phosphorous are key minerals that play a vital role in the formation and maintenance of strong and healthy bones. Both are the primary component of bone tissue, providing the structural framework that supports the body^[3,20].

The relationship between Vitamin D, calcium, phosphorus, and bone is crucial for maintaining bone health^[5,10]. Vitamin D, being a hormone, plays a pivotal role in calcium and phosphorous circulation in the human body^[14,21,22]. It helps in active intestinal and renal absorption of calcium and phosphorus. Additionally, when blood serum calcium level is low, Vitamin D helps mobilize calcium from bone to normalize its concentration in blood^[5,23,24,25].

Insufficient vitamin D interferes with the absorption of an adequate amount of calcium and phosphorus, including during pregnancy and lactation^[25,26,27]. Vitamin D deficiency can lead to various bone-related issues including weakened bones, an increased risk of fractures leading to conditions like osteomalacia and osteoporosis in adults and rickets in children, including early infants life^{[27,28,29,30]}.

In summary, the interplay between calcium, bones, and vitamin D is integral for maintaining strong and resilient skeletal structures.

Extra-skeletal Role of Vitamin D

Scientific investigations in the last three decades have made it clear that in addition to its main role in calcium homeostasis and bone mineralization, Vitamin D is involved in many other important roles.  

Immune System Support: There have been a number of studies highlighting Vitamin D and innate and adaptive immune system relationship that help the body defend against infections and reduce the risk of chronic diseases^[31,32].

T- and B-cells, and macrophages are innate to the immune system. Vitamin D potentially has a function in the regulation of these immune cells, playing a central role in the body's defense against infections^[32,33]. Current studies highlight that Vitamin D is linked to the production of antimicrobial peptides, which are substances that can inhibit the growth of various microorganisms, including bacteria and viruses^[34,35,36].

Anti-inflammatory Properties: Vitamin D is known to have anti-inflammatory properties^[34,36]. It is found to play an important role in the modulation of the inflammation system though inhibition of inflammation-causing agents^[37,38]. Vitamin D deficiency has been linked to several chronic inflammatory diseases, including rheumatoid arthritis and Inflammatory bowel disease^[39,40].

Vitamin D and respiratory health: Ongoing research suggests that vitamin D has a potential role in the prevention of respiratory tract infections^{[41,42,43,44]}. Clinical trials studies suggest a protective role against RTI^[43,45].

Vitamin D-deficiency and auto-immune diseases: It is suggested that Vitamin D-deficiency can lead to increased risk of several autoimmune diseases like multiple sclerosis, diabetes, lupus, and other conditions^{[40,41,46,47]}.

Vitamin D and Cancer: Potential connections between vitamin D and various types of cancer is an area of ongoing research, and scientific studies. There is a protective relationship between sufficient vitamin D status and lower risk of cancer^[48,49,50]. Different studies, including clinical, suggest that there is good evidence that vitamin D reduces the risk of incidence of several different types of cancer^{[51,52,53,54]}. However, the evidences are only suggestive, the findings are not entirely conclusive.

Vitamin D and hypertension: High blood pressure (hypertension) is a global health issue that affects a large proportion of the world's population. Evidence from epidemiological and clinical studies has demonstrated a connection between vitamin D deficiency or insufficiency and high blood pressure^{[55, 56, 57]}.

Recommended Doses

Intake recommendations for vitamin D and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by expert committees of NASEM^[14,51]. General guidelines for vitamin D intake according to the U.S. National Institutes of Health for children (1-8 years), adults (19-70 years) and pregnant/ breastfeeding women is 15 micrograms per day. For 71 years or older adults, the daily recommended dose is 20 mcg, whereas for infants (up to 12  months) it is 10 mcg^[51].  

The recommended dosage of vitamin D varies based on factors such as age, sex, health conditions, and individual needs^[57,59]. Before taking vitamin D supplementation, it is advisable to always consult and follow healthcare provider advice for personalized guidance on vitamin D dosage and intake.

Sources of Vitamin D

Food Sources

Only a limited number of foods naturally contain vitamin D^[51,60]. Good sources of vitamin D are mainly of animal origin (cholecalciferol). Fatty fish like salmon, mackerel, tuna, and fish oils are among the best sources. In addition to these, egg yolk and liver as organ meat are good sources too of the Vitamin D^{[10,51,61,62]}.

There are limited plant-based food options that naturally contain significant amounts of vitamin D (ergocalciferol). Mushrooms, particularly those exposed to sun or artificial ultraviolet (UV) light during growth, can provide good amounts of vitamin D^[63].

In the US and some other countries, various common foods, such as milk, margarine, and breakfast cereals, are fortified with vitamin D to increase its dietary intake during consumption^[60,64]. 

Sunlight

The most natural and primary source of Vitamin D for humans is exposure to direct unobstructed sunlight. When Type B ultraviolet radiation (UVB) with a wavelength of 290-315 nm from the sun penetrates the uncovered skin, a precursor of vitamin D is synthesized in the skin^[1,2,65]. This precursor undergoes further processes in the liver and kidneys to form an active form of vitamin D.

Spending time outdoors, about 10-30 minutes in the sun a few times a week, especially during midday when the sun is at its highest point, can significantly contribute to maintaining adequate Vitamin D levels^[51]. Vitamin D intoxication will not occur in humans regardless of the duration of sun exposure, as any surplus previtamin D3 and vitamin D3 undergo photodegradation^[66,67].

Supplements

The predominant source of vitamin D arises from exposure of the skin to solar radiation, with a comparatively minor contribution from dietary sources. However, people farther North and South during the winter (up to 6 months of the year) often cannot make any vitamin D3 in their skin^[66]. Many factors such as age, skin pigmentation, type of clothing, type of sunscreen can impede sun exposure and thus inhibit cutaneous vitamin D synthesis^[2,66,68].

In cases where obtaining sufficient Vitamin D through sunlight and diet is challenging, dietary supplements can be a viable option^[60,62,69].

Unlike water-soluble vitamins, vitamin D, being fat soluble, is deposited with the fat in the body and stays in the body for a fair period of time. In human serum it has a half-life of 15-25 days^[9,14], whereas in the adipose tissue, it can stay for 3-5 years^[19].

Excessive intake of vitamin D supplements can be harmful. It's crucial to consult with a healthcare professional before starting Vitamin D as dietary supplements to determine the appropriate dosage.

Conclusion

Vitamin D is undeniably a vital component of maintaining overall health and preventing various diseases. While sunlight remains the most natural source, incorporating Vitamin D-rich foods and, if necessary, supplements into your diet can help ensure you receive the optimal levels needed for a healthy and vibrant life.

As with any health-related matter, consulting with a healthcare professional is essential to tailor recommendations to individual needs and circumstances. So, embrace the sunshine to unlock the potential benefits of Vitamin D.

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