Vitamin D: What You Should Know

Sources, Benefits, Forms, Dosage 

What is Vitamin D?

Vitamin D is one of thirteen essential vitamins. Essential vitamins need to be present in the diet because the human body cannot make the nutrients on its own, or in sufficient amounts.1 Vitamin D is considered as an essential vitamin even though it is also produced by the skin as a prohormone, which can be converted into an active hormone in the liver and kidneys, and then communicates with other tissues.1 Along with being essential, Vitamin D is also fat-soluble, which means unlike water-soluble vitamins, these nutrients are stored in the liver and fat cells of fatty tissue. Since the four fat-soluble vitamins, Vitamin A, D, E, and K are stored in tissue and not as easily flushed out of the body, there is a risk to develop toxic side effects. However, toxicity only occurs when the vitamin is taken in very high concentrations.

Benefits of Vitamin D

Vitamin D supports and maintains bone health by promoting bone growth and remodeling.2 Vitamin D regulates and promotes absorption and utilization of the minerals calcium and phosphorous, which in turn also supports bone and dental health.3

In addition to supporting and maintaining the skeletal system, Vitamin D is also involved with cell differentiation and growth, neurological functions, lowering inflammation, and boosting the immune system to fight off illness.1,4 Other research shows it may aid in prevention of certain diseases such as type 2 diabetes, multiple sclerosis, hypertension, and possibly even colon, prostate, and breast cancer.2

Forms of Vitamin D – Which is best?

The two forms of Vitamin D include ergocalciferol or Vitamin D2, and cholecalciferol. Vitamin D3.5 Vitamin D2 is derived from plant and yeast dietary sources.5 Vitamin D3 is the form that is made by the body when exposed to the sun’s UV rays, found in animal food sources, and is also found in lichen which is a cyanobacteria or an algae.5

When Vitamin D is ingested or synthesized in the skin it needs to be metabolized into the active hormonal form, Calcitrol.2 Before metabolizing into the active form, the first conversion of Vitamin D occurs in the liver where it is processed into Calcidiol, and then after is further metabolized in the kidneys into Calcitriol, which assists in calcium absorption.1,2

The most bioavailable and effective form is Vitamin D3 (cholecalciferol), and it is also considered to be the most natural form of Vitamin D.1,3

Sources of Vitamin D – From food and nutrition supplements

Limited food sources contain Vitamin D. Dietary options that contain Vitamin D2 include mushrooms, and Vitamin D3 is found in salmon, tuna, egg yolks, beef liver, and cheese.1,2,4 Since Vitamin D is absent from most food sources, certain products such as breakfast cereals and dairy products are fortified with Vitamin D, which will be indicated on the food label.1,4 Both Vitamin D2 and D3 are used in nutrition supplements.1 When consuming fat-soluble vitamins like Vitamin D, it is best to accompany these nutrients with a dietary fat for optimal absorption.

Vitamin D is also known as the “sunshine vitamin” because it is produced by the body when the skin is exposed to sunlight.4 The production of Vitamin D3 made in skin is dependent on the time of day, season, and skin pigmentation, and production is reduced when the skin is covered by clothing or sunscreen.5 The Vitamin D3 produced by the body is equivalent to the Vitamin D3 in animal food sources.1

Recommended daily dose of Vitamin D – What physicians advise

The recommended daily dose for nutrients is unique to a person’s age, gender, other personal factors, and specifically environmental location for this particular vitamin. For most people, 15 minutes of sun exposure three times per week is sufficient to produce adequate Vitamin D3 levels.1 For this reason, some scientists believe Vitamin D is a nonessential nutrient that does not need to be present in the diet, but can be conditionally essential for those who are unable to produce adequate amounts.1 For the populations that are not exposed to enough sunlight, tanning beds are not a recommended resource to obtain sufficient amounts of Vitamin D as the risks of skin cancer outweigh the pros.1

The Food and Nutrition Board (FNB) established a recommended dietary allowance (RDA) for Vitamin D to ensure sufficient bone health and proper calcium absorption.2 The RDA amounts in Table 1 are a reference for nutritional adequacy in healthy individuals. The RDA of Vitamin D for adults is the same for both women and men, which is 15 mcg (micrograms) or 600 IU (International Units).

Recommended Dietary Allowance (RDA) of Vitamin D
Infants (0 – 12 months) 10 mcg/day
Children (1 -8 years) 15 mcg/day
Adolescents (9 – 18 years) 15 mcg/day
Adults (19 – 70 years) 15 mcg/day
Adults (70+ years) 20 mcg/day
Pregnant and Lactating Women 15 mcg/day

Table 1: Daily Vitamin D Recommended Dietary Allowance (RDA) to Meet the Needs of Healthy Individuals2

Certain populations may need to be more mindful when evaluating their Vitamin D needs. Those using inflammation-reducing medications such as steroids can inhibit Vitamin D metabolism and absorption, which can cause further health complications.2 With any particular medication or health condition it is always best to consult with your primary healthcare provider before taking the Healthycell® products or any nutrition supplement.

Vitamin D toxicity is uncommon

Vitamin D toxicity is uncommon from food sources and sun exposure, and is only typically seen when consuming very high doses in nutrition supplements.2 Consumption must exceed over 25 mcg/day (4,000 IU) for an extended period to become toxic.2,5 It is possible for Vitamin D to become toxic when supplementing high doses because it causes Calcium levels to increase which can cause hypercalcemia and hypercalciuria.1 Hypercalcemia occurs when there is too much Calcium in the blood stream, and hypercalciuria occurs when there is too much Calcium in urine, which can further result in kidney stones.1,8 Other symptoms of toxicity are bone loss, anorexia, nausea, and in the most extreme cases, even death.1,5 To avoid toxicity, a maximum level that may cause an adverse event, also known as a tolerable upper intake level (UL) shown in Table 2 has been set for Vitamin D.

Tolerable Upper Intake Level (UL) of Vitamin D
Infants (0 – 12 months) 25-38 mcg/day
Children (1 -8 years) 63-75 mcg/day
Adolescents (9 – 18 years) 100 mcg/day
Adults (19+ years) 100 mcg/day
Pregnant and Lactating Women 100 mcg/day

Table 2: Daily Vitamin D Tolerable Upper Intake Level (UL)2

Vitamin D deficiency, symptoms, and people at risk

Vitamin D deficiency is a common nutrient deficiency. When children are deficient it results in inadequate bone mineralization, and they become susceptible to bone fractures and developing rickets, which is characterized by soft bones, improper bone growth, and skeletal deformities in the legs.1,2 Vitamin D deficiency in adults results in a condition called osteomalacia – soft and weak bones that are prone to fracture due to poor bone mineralization and high bone demineralization.1,5 Adults who are deficient in Vitamin D tend to have low bone mineral density (BMD), and are also at risk of bone fractures and developing osteoporosis.1,6

Less severe conditions of deficiency are appetite loss, weight loss, nausea, diarrhea, burning of the mouth and throat, and vision issues.3 Those who are at risk for Vitamin D deficiency are those with inadequate Vitamin D absorption, those who neglect Vitamin D rich or fortified foods, malnourished vegetarians or vegans, people with darker skin, those who live far from the equator or are exposed to little sunlight, and the older population.1

Vitamin D in Healthycell® Pro – Only the best form

The type of Vitamin D really matters to your health. Healthycell® uses only the best form of Vitamin D, which is Vitamin D3, in the form of natural cholecalciferol from Lichen, known by the registered name Vitashine®. The dosage of Vitamin D3 in Healthycell® and Healthycell® Pro is 500 IU (International Units) in the morning formula and 500 IU in the evening formula, for a daily dose of 1,000 IU or 12.5 mcg, satisfying 250% of the Daily Value (%DV). Nutrition supplement labeling and food labeling guidelines use Reference Daily Intake (RDI) as the standard for dosage.


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National Library of Medicine, 11 Feb. 2016. Web. 13 Sept. 2016.

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(2011): 585-91. Web.

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Marjo H. Knapen, Irene M. Van Der Meer, Albert Hofman, and Jacqueline C.M.

Witteman. “Dietary Intake of Menaquinone Is Associated with a Reduced Risk of

Coronary Heart Disease: The Rotterdam Study1.” The Journal of Nutrition 134 (2004):

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Nov. 2004. Web. 15 May 2017.

8. Wisse, Brent, MD, David Zieve, MD, MHA, and Isla Ogilvie, PhD. “Hypercalcemia:

MedlinePlus Medical Encyclopedia.” Hypercalcemia: MedlinePlus Medical Encyclopedia.

US National Library of Medicine, 03 Feb. 2016. Web. 15 Sept. 2016.