Vitamin D, which is also known as calciferol, is a fat-soluble vitamin that is present in some foods, and also produced by the human body under certain conditions — specifically, when your skin is exposed to the sun’s UV rays.
According to the Office of Dietary Supplements of the National Institutes of Health, the vitamin D that your body produces from sunlight exposure is biologically inert, and your body needs to perform certain processes to activate it. These processes are called hydroxylations, and they happen primarily in the liver and kidney.
The main type of vitamin D that’s used by the human body is called vitamin D3 or cholecalciferol.
Functions of vitamin D
Vitamin D plays an extensive role in human health. According to the Harvard T.H. Chan School of Public Health, one of the main functions of vitamin D is helping the body absorb and retain calcium and phosphorus, which are essential for bone health.
Vitamin D works by promoting calcium absorption in the gut, and it’s also involved in regulating levels of calcium and phosphorus in your blood. This enables bone building and mineralization, and it’s also needed for bone remodeling and normal growth.
However, vitamin D plays numerous other roles in the body. According to the Mayo Clinic, this vitamin also acts as an anti-inflammatory, antioxidant, and neuroprotective substance. Many of the cells in your body have receptors for vitamin D, which explains why the side effects of low vitamin D levels are so varied. Overall, the functions of vitamin D include:
- Bone health, growth, and remodeling
- Inhibiting the growth of cancer cells
- Helping control infections
- Boosting the immune system
- Reducing inflammation throughout the body
- Decreasing the risk of heart disease
- Participating in glucose metabolism to help prevent diabetes
- Regulating mood and lowering the risk of depression
Causes of vitamin D deficiency
Vitamin D deficiency is still relatively common in many places around the world, and cases tend to go up during the winter months or in places with a low UV index. It has been estimated that up to 1 billion people in the world have extremely low vitamin D levels. According to StatPearls, the causes of chronic low vitamin D levels include:
- Decreased dietary intake
- Malabsorption disorders
- Decreased sun exposure
- Chronic liver disease
- Renal failure
- Hereditary vitamin D resistant rickets
Medications that cause vitamin D deficiency
Low vitamin D levels can also be caused by the consumption of certain medications, including:
If you’re on any of these medications, your doctor could order regular vitamin D tests to monitor your levels and prescribe a supplement to prevent disease due to lack of vitamin D.
All vitamin D deficiency symptoms
The symptoms of low vitamin D can range in severity. In children, severe vitamin D deficiency can lead to a condition called rickets. According to the Cleveland Clinic, the signs of rickets can include:
- Incorrect growth
- Bowed or bent bones
- Bone pain
- Muscle weakness
- Joint deformities
A vitamin D deficiency in adults can lead to milder symptoms, which can make it difficult to detect. Signs of low vitamin D in adults can include:
- Bone weakness
- Mood changes
- Muscle pain
- Muscle cramps
- Muscle weakness
One of the main side effects of a lack of vitamin D is osteomalacia and osteoporosis, which can increase your risk of fractures.
How do you know if you have a vitamin D deficiency?
If you’re showing signs of vitamin D deficiency, your doctor could order certain tests to accurately measure your serum levels. According to MedlinePlus, a vitamin D test is a blood test that doesn’t require any special preparations on your part.
How to fix vitamin D deficiency
The easiest and most effective way to treat lack of vitamin D symptoms is to increase your exposure to sunlight.
Low vitamin D level treatment usually requires at least 10-30 minutes of midday sunlight exposure, although people with darker skin tones may need to be exposed to the sun for longer periods. But remember that excessive sunlight can increase your risk of skin cancer and other skin diseases — it’s always important to apply sunscreen if you’re going to be out in the sun.
There are different types of vitamin D supplements for the treatment of vitamin D deficiency. You may see vitamin D3 or cholecalciferol, and vitamin D2 or ergocalciferol supplements available.
Vitamin D2 is sourced from plants, and it’s the form that can be found in fortified foods. Vitamin D3, on the other hand, is the type of vitamin D that’s naturally produced in your body and it can be found in animal sources. According to a study published in the Journal of Clinical Endocrinology and Metabolism, vitamin D3 increases total vitamin D levels more effectively than vitamin D2 supplements.
Dietary sources of vitamin D include:
- Cod liver oil
- Tuna fish
- Beef liver
- Egg yolks
- Fortified dairy and plant-based milks
- Fortified orange juice
- Fortified cereals
Vitamin D - ods.od.nih.gov
Vitamin D - hsph.harvard.edu
Vitamin D - mayoclinic.org
Vitamin D Deficiency - ncbi.nlm.nih.gov
Vitamin D Deficiency - my.clevelandclinic.org
Vitamin D Test - medlineplus.gov