RDA and Sources
Vitamin D is a necessary fat-soluble nutrient with various functions and sources. The recommended dietary allowance (RDA) primarily depends on the individual’s age, while sex is an insignificant factor. Namely, infants (up to 12 months) require 10 mcg, people from 12 months to 70 years old need 15 mcg, and older adults require 20 mcg daily (“Vitamin D,” 2022). The amount does not change for pregnant women, and 15 mcg is a sufficient intake. Consequently, Vitamin D is a unique nutrient since its RDA can be achieved exclusively via sun exposure (Insel et al., 2018). In addition, individuals can obtain dietary Vitamin D from eating white fish (rainbow trout and salmon are the best sources), milk, eggs, pork ribs, and fruit yogurt.
Vitamin Absorption
The absorption mechanism depends on the vitamin intake type (sunlight exposure/dietary) and compound (D2 and D3 are the most significant). When the ultraviolet (UV) reaches the skin, it transforms cholesterol into cholecalciferol, which can also be obtained via animal products (Insel et al., 2018). Next, cholecalciferol is converted into 25-hydroxyvitamin D3 in the liver and 1,25-dihydroxyvitamin D in the kidneys, allowing for consequent absorption (Charoenngam et al., 2019). Therefore, liver and kidney health are paramount in adequate vitamin D absorption and can either enhance or hinder the process (Insel et al., 2018). Other features of nutrient intake (improper foods and excessive usage of sunscreen) also affect the quality of absorption.
Functions and Importance
Vitamin D is essential for proper body functioning, significantly enhancing bone health and allegedly preventing cancer/cardiovascular diseases. The nutrient is also considered a hormone and serves as a regulator of insulin formation/secretion (Insel et al., 2018). Nevertheless, the primary role of Vitamin D is the management of blood phosphorus and calcium levels, which are essential for bone, intestine, and kidney health (Insel et al., 2018). The majority of these functions are enabled by D2 and D3 compounds. Ultimately, adequate Vitamin D intake is important because of its significant impact on various elements of body functioning, particularly bone health.
Vitamin Deficiency
Vitamin D deficiency has multiple adverse effects and should be avoided via proper sun exposure and dietary intake. Namely, the negative consequences include skeletal issues (bone loss, fractures, osteoporosis) and elevated risks of infections/cardiovascular diseases (Amrein et al., 2020). In the United States, Canada, and European countries, approximately 20 to 80% of all individuals have inadequate Vitamin D levels (Insel et al., 2018). It is immensely difficult to accurately assess the prevalence of nutrient deficiency, but most authors agree that nearly one billion individuals globally are affected (Insel et al., 2018). The severity of the problem depends on average sun exposure (geography and lifestyle), nutrition habits, and obesity levels, which affect kidney, liver, and gut health.
Toxicity and Tolerable Intake
Vitamin D is not excessively toxic, but there are notable adverse effects if the individual exceeds the tolerable upper intake level (UL) of 4,000 IU or 100 mcg. Sun exposure cannot produce such doses, meaning that only supplement megadoses can lead to Vitamin D toxicity (Insel et al., 2018). The most adverse consequence of exceeding UL is the elevated concentration of calcium in the blood, which can be transferred to the kidney, heart, lungs, and blood vessels (Insel et al., 2018). In turn, the unbalanced distribution of calcium in soft tissue can lead to such symptoms as nausea, depression, loss of bone mass, vomiting, and a lack of appetite (Insel et al., 2018). In summary, it is critical that individuals do not exceed a daily UL of 100 mcg and contact professionals before consuming supplement megadoses of Vitamin D.
Usage in Therapies
At present, there is conflicting evidence regarding the usage of Vitamin D to treat some medical conditions. For instance, it is clear that the nutrient is paramount in preventing bone-related diseases, such as sclerosis and rheumatoid arthritis (Insel et al., 2018). However, the research produces inconsistent results regarding the impact of Vitamin D on non-skeletal outcomes, including the treatment of cancer, diabetes, and autoimmune diseases (Charoenngam et al., 2019). There is a particular ongoing interest in the integration of Vitamin D into cancer therapies (Insel et al., 2018). However, according to most studies, the nutrient is highly likely to be effective in treating these conditions, but more research is necessary to draw definitive conclusions.
Interesting Facts
As mentioned before, Vitamin D is an exceptional nutrient with multiple fascinating qualities and characteristics. For instance, the mechanism of absorption via sun exposure is complex and might affect people differently since individuals have varying skin hues (Insel et al., 2018). Moreover, geographic location plays a critical role in this process, as residents of Portland and Seattle have elevated risks of nutrient shortage compared to people living in Los Angeles and Miami (Insel et al., 2018). Another interesting fact is that some authors attribute Vitamin D deficiency in the United States to the removal of dairy products from typical nutrition (Insel et al., 2018). While milk might not be the best source of nutrients, it used to be more prominent in daily food intake among American residents in the 20th century.
References
Amrein, K., Scherkl, M., Hoffmann, M., Neuwersch-Sommeregger, S., Köstenberger, M., Tmava Berisha, A., Martucci, G., Pilz, S., & Malle, O. (2020). Vitamin D deficiency 2.0: An update on the current status worldwide. European Journal of Clinical Nutrition, 74(11), 1498-1513. Web.
Charoenngam, N., Shirvani, A., & Holick, M. F. (2019). Vitamin D for skeletal and non-skeletal health: What we should know. Journal of Clinical Orthopaedics and Trauma, 10(6), 1082-1093. Web.
Insel, P., Ross, D., McMahon, K., & Bernstein, M. (2018). Discovering nutrition (6th ed.). Jones & Bartlett Learning.
Vitamin D. (2022). National Institute of Health: Office of Dietary Supplements. Web.