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Vitamin D is a vital nutrient that directly or indirectly facilitates a variety of critical physiological processes.
Its most important feature is it allows the body to absorb calcium effectively, which is then used for building and repairing bones and teeth and maintaining a healthy immune system to ward off diseases.
Vitamin D is also involved in maintaining phosphate and magnesium balance within the body.
Metabolization of Vitamin D in the Body
It is important to understand that vitamin D exists in many forms, with vitamin D3 and D2 being the most relevant to health. (1)
The primary source of vitamin D is made by the body, but you can also supplement with diet-based vitamin D. The latter is derived from both plant and animal sources. Vitamin D made by the body must go through a chemical reaction that is completed only after exposure to the UV rays in sunlight.
Both endogenous vitamin D (the form made by the body) and exogenous vitamin D (obtained for the diet) are stored in the skin cells in an inactive form.
Activation to the form that allows the vitamin to perform its vital function occurs in two stages. The inactive form is carried by the blood first to the liver, where a chemical reaction occurs to change its form, then to the kidneys, where the final activation happens. (2) The vitamin is now ready to perform its many actions.
Blood tests that measure vitamin D levels measure the two forms that are present after each step.
Causes of Vitamin D Deficiency
The following factors can contribute to the development of vitamin D deficiency:
1. Limited exposure to the sun
Studies show that the number of people with vitamin D deficiency is much larger than previously recognized. (3)
Vitamin D deficiency occurs primarily due to limited exposure to sunlight. Therefore, risk factors that lead to one getting limited sun exposure are also risk factors for vitamin D deficiency.
Limited exposure to the sun can be caused by living in colder climates, certain jobs, excessive use of sunblock, increasing age or disability, cultural requirements that restrict skin exposure, or living in a very polluted area.
2. People with dark skin
People with increased melanin and therefore darker skin have more difficulty absorbing UV rays and are also at higher risk.
3. Certain medical conditions
Problems with the gastrointestinal tract, such as medical conditions that affect the lining of the gut, can reduce vitamin D absorption from foods eaten.
Similarly, conditions that affect the kidneys and liver, such as chronic kidney disease or cirrhosis, can decrease the body’s ability to activate the vitamin, thereby leading to a deficiency.
Obese patients may also be at risk. Vitamin D is pulled from the blood and stored in fat cells, decreasing the amount of circulating vitamin D needed for action.
5. Restrictive diets
People on restrictive diets, such as vegans, may also be prone to a deficiency because it deprives them of the main food sources of vitamin D such as eggs, fatty fish, and fortified dairy products.
Signs of Vitamin D Deficiency
Vitamin D deficiency can manifest in the following ways:
1. Weak bones and osteoporosis
Vitamin D allows the body to absorb calcium, which is very important for bone health, so a deficiency may lead to an increased risk of broken bones, such as stress fractures or an increased risk of a break following a minor injury. People with osteoporosis in addition to a deficiency are particularly at risk. (4)
A deficiency can also lead to generalized bone and muscle pain and a decrease in the body’s ability to heal a broken bone.
In the last decade, medical research has revealed vitamin D’s important role throughout the body. Deficiencies have been traced to impaired immunity and increased risk and/or severity of certain infections.
Most recently, there has been a connection between vitamin D deficiency and COVID-19 disease severity.
3. Other symptoms
Other vitamin D deficiency symptoms are:
- Cardiovascular disease
- High blood pressure
- Sudden changes in mood, including bouts of depression
- Cognitive impairment
- Generalized fatigue
- Muscle pain
- Hair loss
- Slow wound healing
Treatment for Vitamin D Deficiency
It is important to know that with adequate sun exposure, endogenous vitamin D is all the body needs.
To supplement a deficiency, however, exogenous vitamin D is necessary and occurs in the form of vitamin supplements or eating foods rich in vitamin D2 or D3. Animal products, such as meat, dairy, eggs, and fish, are the main sources of vitamin D3, (5) while vitamin D2 comes from plants. Vitamin D3 and D2 function similarly in the body.
Do Home Remedies Work?
There are no particular home remedies to boost vitamin D levels in the body. However, these foods naturally contain vitamin D:
- Canned sardines
- Pork chops
- Egg yolks
- Soy milk
- Cheddar cheese
- Fortified orange juice
- Fortified milk
- Fortified tofu
- Fortified yogurt
Apart from these, sunlight (in moderation) is one of the best natural sources of vitamin D for the human body. If you are unable to get sunlight, your doctor may advise you to take vitamin D supplements.
Recommended Intake of Vitamin D
The amount of vitamin D needed by the body is dependent on many factors and differs somewhat depending on the organization cited. In general, optimal intake is between 600 IU and 800 IU daily for adults. (6) For premenopausal women and nongeriatric adults (<65 years old), 600 IU a day may be adequate.
Postmenopausal women, elderly patients, and osteoporotic patients may need between 800 IU and 1000 IU daily. (7) Children under 16 may supplement with 400 IU daily.
ALSO READ: What Is Vitamin D? How Much You Need, Sources and More
Vitamin D deficiency is common and is linked to many conditions. Adequate sunlight exposure is key. Have your doctor test you twice a year for vitamin D, especially if you have risk factors for a deficiency.
Vitamin D supplements are likely needed for most people. However, it is important to remember that calcium intake must also be adequate for vitamin D to exert its effects. If enough calcium is not taken in the diet, it should also be supplemented.
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