Clinical Quick Reference Monthly Newsletter / March 2023 – Vitamin D – A Key Micronutrient
Clinical Quick Reference Guides – Vitamin D
This guide will provide a brief overview of vitamin D.
What is Vitamin D?
Vitamin D is a fat-soluble vitamin. Vitamin D is present in some foods and also available as a supplement.
Additionally, when UV rays from the sun strike the skin, an endogenous form is produced. This leads to the synthesis of vitamin D.
Fat Soluble Vitamins
Vitamins A, D, E, and K are referred to as fat-soluble vitamins. This is because fat-soluble micronutrients are soluble in organic solvents and are absorbed/transported in a way that is similar to fats.
The Fat Soluble Vitamins:
Vitamin A
Vitamin D
Vitamin E
Vitamin K
Vitamin D “Activation”
It is essential that we understand the vitamin D obtained from foods, supplementation and sun exposure is biologically inert. These varieties must undergo hydroxylations to become active.
Vitamin D Activation Steps
The first hydroxylation occurs in the liver.
During this process, vitamin D is converted to 25-hydroxyvitamin D. This form may also be known as “calcidiol.”
The second hydroxylation occurs primarily in the kidney.
This hydroxylation forms the physiologically active 1,25-dihydroxyvitamin D ( calcitriol).
Vitamin D in Food and Supplementation
Two primary forms of Vitamin D are found in foods and dietary supplements. These are D2; “ergocalciferol” and D3; “cholecalciferol.”
Both kinds are well absorbed in the small intestine. There are only a few foods that naturally contain vitamin D.
In the United States, fortified foods provide the majority of dietary vitamin D.
The vitamin is added to many breakfast cereals and some margarines, orange juices, and yogurts.
Almost all of the U.S. milk supply is fortified.
Fatty fishes and fish liver oil are usually excellent (natural) sources of vitamin D.
Cheese, egg yolk and beef liver also naturally contain small amounts.
Vitamin D Supplements
Photo by Maria Kozyr on Unsplash What kinds of vitamin D dietary supplements are available?
In addition to dietary intake, vitamin D is also available in supplements that generally contain only vitamin D or: vitamin D with a few other micronutrients.
The two forms available are:
D2 (ergocalciferol)
and D3 (cholecalciferol)
Note:
Because this vitamin is fat soluble, it is best that it be taken with a meal/snack that includes a small amount of fat.
Vitamin D Micronutrient Roles in the Human Body
Vitamin D assists in the absorption of calcium and maintenance of adequate serum calcium and phosphate concentrations. This function helps promote bone mineralization. It also guards against the involuntary contraction of muscles associated with hypocalcemic tetany.
It is crucial for normal bone growth and bone remodeling. When intake is insufficient, bones can become thin, brittle, or even misshaped. Proper intake prevents rickets in children and osteomalacia in adults.
When taken with calcium, vitamin D can protect older adults from osteoporosis.
Other Roles
Vitamin D plays a vital role in other body functions and processes. This essential micronutrient has been found to help reduce inflammation. Researchers have also discovered that it plays a crucial role in modulating functions related to cellular growth, immune functions and the metabolism of glucose.
Beyond these processes, vitamin D modulates many genes active in cell processes related to cellular apoptosis (programmed cell death), differentiation, and proliferation.
Interesting note:
Many body tissues have vitamin D receptors
Vitamin D Overview
Assists in development of strong bones
Helps protect older adults from osteoporosis
Vitamin D deficiency can lead to bone diseases, including rickets in children and osteomalacia in adults
Vitamin D assists the immune system
Vitamin D is required for normal muscle and nerve function
Research suggests that vitamin D deficiency may be widespread
Bodies make vitamin D from sunlight (but this can be affected by geography, skin color, air pollution, and other related factors)
Remember that sunlight (UV) exposure needs to be within recommended standards as overexposure can lead to skin cancer
VITAMIN D (NIH Daily Recommendations)
Birth to 12 months
10 mcg (400 IU)
Children 1–13 years
15 mcg (600 IU)
Teens 14–18 years
15 mcg (600 IU)
Adults 19–70 years
15 mcg (600 IU)
Adults 71 years and older
20 mcg (800 IU)
Pregnant and breastfeeding teens and women
15 mcg (600 IU)
Conditions That May Affect Vitamin D Levels
Some individuals may have more difficulty getting enough of this key micronutrient.
Per the CDC/NIH:
Breastfed babies; this is because breast milk alone can not provide vitamin D. They recommend that breastfed infants be given a supplement that includes 10 mcg (400 IU) of vitamin D per day.
Older adults; As individuals age, their skin’s ability to make vitamin D when exposed to sunlight declines.
People with little exposure to sunshine because they do not go outside or keep their bodies and head covered. Sunscreen also limits the amount of vitamin D produced.
People with dark skin. The darker your skin, the less vitamin D you make from sunlight exposure.
People with conditions that can affect fat absorption; for example, Crohn’s disease, celiac disease, or ulcerative colitis.
People who have an obesity diagnosis or those who have undergone gastric bypass surgery; They may require more vitamin D than others.
Vitamin D Levels/Medical Testing
Testing can help identify if a person has sufficient intake of vitamin D.
A blood test can measures the amount of vitamin D in the blood. During the study, a form of vitamin D called “25-hydroxyvitamin D,” is measured.
According to the US National Institutes of Health:
50 nmol/L (20 ng/mL) or above is adequate for the majority of people
Levels under 30 nmol/L (12 ng/mL) are considered too low and may contribute to weak bones and poor health
Levels above 125 nmol/L (50 ng/mL) are considered too high and may contribute to health issues.
Medical Terminology
Getting to know these terms will help reinforce the above material.
hypercalcemia - condition in which the calcium level in the blood is above normal
hypocalcemia – treatable condition that occurs when calcium levels in the blood are too low
tetany – symptom that is characterized by involuntary contraction of muscles usually resulting from low calcium levels in the blood
Helpful videos:
Disclaimer: The above study guide and resources represent study materials; always seek and follow the advice of your medical provider for any acute or chronic medical issues or questions, and follow the protocols of your program or supervising agency.
Resources:
CDC
NIH
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