Sunshine Vitamin D and Its Functions


Proper nutrition hinges on multiple factors, and one of them is vitamins. One of the vitamins that are particularly important but also often deficient in humans is vitamin D. In this report, vitamin D will be discussed together with its key related topics, including its functions, sources, and the issues that can be associated with its deficiency or excess. The paper will demonstrate that this vitamin is crucial for the musculoskeletal system and has many other important functions, which is why the prevalence of its deficiency is a major issue that is exacerbated by the possibility of vitamin D overdose.

Vitamin D and Its Functions

Vitamin D is one of the micronutrients that are required for the functioning of a human body. They are needed in small amounts, and ideally, a state of homeostasis should be achieved with the appropriate intake (through food or other sources), excretion (especially through urination and sweating), and degradation of vitamins (Office of Dietary Supplements [ODS], 2019; Zhou, 2015). In order to become biologically active, vitamin D, which is fat-soluble, needs to be absorbed from the gut and transformed by the liver and kidneys into calcidiol (25-hydroxyvitamin D) and calcitriol (1,25-dihydroxyvitamin D) respectively (ODS, 2019; Zhou, 2015).

After that, it can perform a number of functions; among other things, it is required for the immune system, and it participates in reducing inflammations (ODS, 2019). In addition, according to ODS (2019), it is a part of cell growth mechanisms, and it might prevent cancer. In general, the functions of this vitamin are both crucial and numerous.

Most importantly, however, vitamin D is associated with calcium and the musculoskeletal system. It is responsible for ensuring “adequate serum calcium and phosphate concentrations” and facilitating “calcium absorption” (ODS, 2019, par. 2). In other words, this vitamin is required for healthy bones in humans (their formation, remodeling, and mineralization) and for the prevention of tetany. ODS (2019) notes that sufficient levels of the vitamin are necessary for preventing rickets (children), osteomalacia (adults), and osteoporosis (older adults). Overall, the role of this vitamin is vital, which is why it is important for humans to find the means of acquiring it.


There are two primary sources of vitamin D: food and sunlight. The latter is the reason why this vitamin is sometimes called the “sunshine vitamin.” Indeed, due to the influence of ultraviolet rays, which are a part of sunlight, on human skin, the production of this vitamin is set in motion (ODS, 2019; Zhou, 2015). People who live in regions where the day is shorter have fewer opportunities to produce the vitamin; also, cloudiness and smog, as well as skin melanin or the use of sun screens, can modify the body’s reaction (ODS, 2019; Schoor & Lips, 2018).

Up to 60 minutes of exposure per week should provide a sufficient amount of the vitamin provided that it occurs during the day (before 3 pm and no earlier than 10 am) (ODS, 2019). Overall, sunlight can be a reliable method of ensuring the presence of vitamin D in one’s body.

On the other hand, foods are not a very effective source of the vitamin because few products contain it. Particular types of fish and their oils can offer substantial amounts; also, egg yolks, some dairy products, certain meats (for example, beef liver), and some mushrooms may serve as a source (ODS, 2019; Schoor & Lips, 2018). In some countries, including the US and Canada, dairy products can be fortified to contain the vitamin (ODS, 2019). However, many people’s diets do not incorporate enough vitamin D foods. According to ODS (2019), men and women generally consume about 204-288 and 144-276 International Units (IUs) of it a day (respectively), even though around 400 IUs are recommended. The lack of vitamin D, as well as its excess, can cause significant problems.

Issues with Vitamin D and Their Prevalence

The levels of the vitamin in human bodies are evaluated with the help of one of the vitamin’s metabolites. Currently, it is assumed that no less than 50 nmol/l (and no more than 150 nmol/l) of 25-hydroxyvitamin D should be found in the serum of an adult person (ODS, 2019; Schoor & Lips, 2018). The data aggregated by the National Center for Health Statistics (2018), as well as some other sources (Schoor & Lips, 2018), can be used to make conclusions about the prevalence of vitamin D issues in different groups of the population, which require a detailed discussion.

Deficiency: Causes, Consequences, and Solutions

Vitamin D’s deficiency is a self-explanatory term, but from the perspective of clinical definitions, its concentration is important. Currently, the vitamin’s deficiency is identified as the level of 25-hydroxyvitamin D that is below 25 nmol/l (Schoor & Lips, 2018). In the US, recent data suggest that inadequate amounts of vitamin D are found in about 18% of the population, and 5% demonstrate actual deficiency (Herrick et al., 2019). Therefore, the problem is rather prevalent, which can be explained by its numerous causes.

A large number of the causes of vitamin D deficiency have been determined. The most obvious ones are the lack of access to sufficient amounts of light and appropriate nutrients (ODS, 2019; Zhou, 2015). Additional causes include problems with the body’s ability to convert the vitamin or absorb it (ODS, 2019). Furthermore, increased need for the vitamin can be noted (for example, in children), as well as various disturbances that cause its increased excretion (ODS, 2019; Schoor & Lips, 2018). Overall, there are multiple reasons for the vitamin’s concertation to drop dramatically.

Particular populations that experience higher risks of developing the condition have been identified. People who are unlikely to receive proper nutrition (for example, poor people) or enough sunlight (for example, people with limited mobility), are among the endangered groups (Schoor & Lips, 2018). Breastfed children cannot obtain enough vitamins due to their lack in human milk, and for older adults, the skin’s ability to produce the vitamin is decreased (ODS, 2019; Schoor & Lips, 2018; Zhou, 2015).

Pregnancy also puts one at risk, and people with darker skin are more likely to be affected (Herrick et al., 2019; Schoor & Lips, 2018). As a result, for example, pregnant black women or pregnant non-western migrants tend to have low vitamin D concentrations (Schoor & Lips, 2018; Zhou, 2015). Thus, the causes of the vitamin’s deficiency are especially prominent in some groups, which is why it affects them disproportionately, causing many negative effects.

The symptoms of vitamin D deficiency may differ depending on the age of the patient. In particular, for children, “joint swelling and deformations” can be observed, but for adults, the most common issues include “muscle weakness, bone pain and fractures” (Schoor & Lips, 2018, pp. 671-672). In addition, as it was noted, sufficient amounts of the vitamin prevent musculoskeletal disorders, and its deficiency causes some of them, including rickets and osteomalacia (ODS, 2019). The solution is the increase of vitamin D intake, as well as the management of particular symptoms; vitamin D-heavy products (in particular, fish liver oil) can even reverse the effects of rickets in children (ODS, 2019). However, while treating someone with vitamin D deficiency, it is important to avoid vitamin D overdose.

Excess: Causes, Consequences, and Solutions

Research suggests that excesses of the vitamin are unlikely to occur naturally. Sunlight cannot cause it because prolonged exposure and heating of skin results in the vitamin’s degradation, and consuming the amount of food required to achieve toxic levels is very difficult (ODS, 2019). However, ODS (2019) reports that vitamin D excess becomes probable when a person takes a lot of supplements. Endogenous causes are also possible, and they can be associated with lymphomas, granulomas, and idiopathic infantile hypercalcemia (Marcinowska-Suchowierska, Kupisz-Urbańska, Łukaszkiewicz, Płudowski, & Jones, 2018). As reported by Marcinowska-Suchowierska et al. (2018), it can be assumed that toxic levels of the vitamin are rare, although there is little evidence about the prevalence of the issue.

According to Marcinowska-Suchowierska et al. (2018), toxic levels of vitamin D are achieved with the concentration of 25-hydroxyvitamin D that exceeds 375 nmol/l. The consequences of vitamin D levels which are that high are very dangerous. People with this condition can experience irregular heartbeat, excessive urination (with subsequent dehydration), and weight loss; in addition, they might develop anorexia (Marcinowska-Suchowierska et al., 2018; ODS, 2019).

Vomiting, confusion, and pain in the abdominal area are also possible (Marcinowska-Suchowierska et al., 2018). Importantly, however, any excess of the vitamin is connected to increases in calcium level, which, in turn, is dangerous for numerous organs, including the elements of the cardiovascular system and kidneys (ODS, 2019). It is noteworthy that due to the increases in supplement intake, a spike in vitamin D excess might occur (Marcinowska-Suchowierska et al., 2018; Zhou, 2015). As a result, paying attention to this issue is important despite its rarity.

The first action that is required when a person with a Vitamin D overdose experiences its effects is the discontinuation of the supplement that they are using. However, toxic levels of the vitamin can remain present in the body for days or months (depending on what caused the overdose) (Marcinowska-Suchowierska et al., 2018). As a result, it is necessary to reduce the levels of plasma calcium with the help of glucocorticoids and introduce solutions to managing individual symptoms (for example, hydrating patients in cases of dehydration) (Marcinowska-Suchowierska et al., 2018). This way, the issue of vitamin D excess can be resolved.


The functions of vitamin D are predominantly (but not exclusively) connected to the musculoskeletal system, which makes it critical for human health. Since its primary sources are select foods and sunlight, which may be lacking in particular areas, the 5% prevalence of the deficiency is understandable. However, the lack of the vitamin is also associated with multiple health problems, most of which are related to bones.

The primary solution is increasing the vitamin’s intake; however, it is important to be moderate and avoid overdoses. The latter issue is not very likely to occur naturally, but due to the ubiquity of supplements, the rates of vitamin D overdose might increase in the near future. To summarize, the importance of this vitamin is apparent, and given the health problems that are associated with disbalances in its homeostasis, the methods of ensuring the latter need to be researched and shared with the population.


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Marcinowska-Suchowierska, E., Kupisz-Urbańska, M., Łukaszkiewicz, J., Płudowski, P., & Jones, G. (2018). Vitamin D toxicity–a clinical perspective. Frontiers in Endocrinology, 9, 1-7. Web.

National Center for Health Statistics. (2018). NHANES 2015-2016 [Data files]. Web.

Office of Dietary Supplements. (2019). Vitamin D: Fact sheet for health professionals. Web.

Schoor, N., & Lips, P. (2018). Worldwide vitamin D status. In D. Feldman, J. Pike, & R. Bouillon (Eds.), Vitamin D (4 ed., Vol. 2, pp. 15-40). London, UK: Academic Press.

Zhou, S. (2015). Vitamin paradox in obesity: Deficiency or excess? World Journal of Diabetes, 6(10), 1158-1167. Web.