What is Vitamin D?

Vitamin D is a vitamin that is essential for the body to absorb calcium and phosphorus from the diet. Vitamin D deficiency can lead to bone problems such as rickets in children, and osteomalacia in adults.

Vitamin D can be obtained from the diet or from exposure to sunlight. Vitamin D supplements are also available.

What are the health benefits of Vitamin D?

Vitamin D is important for bone health. It helps the body to absorb calcium and phosphorus from the diet, and to deposit these minerals in the bone. Vitamin D deficiency can lead to bone problems such as rickets in children, and osteomalacia in adults.

Vitamin D is also important for immune system health. Vitamin D deficiency has been linked to an increased risk of respiratory infections, such as influenza.

Vitamin D may also have other health benefits, such as reducing the risk of certain types of cancer, and improving muscle function.

What are the risks of taking Vitamin D supplements?

Taking Vitamin D supplements in large doses (more than 4,000 IU per day) can cause Vitamin D toxicity, which can lead to problems such as high blood calcium levels and kidney stones. Vitamin D toxicity is rare, but it can be serious if it is not treated.

Vitamin D supplements can also interact with certain medications, such as bisphosphonates, which are used to treat osteoporosis. Therefore, it is important to speak to a healthcare professional before taking Vitamin D supplements.

How much Vitamin D do I need?

The amount of Vitamin D that you need depends on your age, your skin tone, and whether you spend time indoors or outdoors.

In general, adults need 600 IU (international units) of Vitamin D per day, and children need 400 IU per day. However, some people may need more Vitamin D than this, and your healthcare professional can advise you on the right amount for you.

Vitamin D is found in a variety of foods, including oily fish, eggs, and fortified cereals. Vitamin D can also be obtained from exposure to sunlight.

When should I take Vitamin D supplements?

If you are not getting enough Vitamin D from your diet or from exposure to sunlight, you may need to take Vitamin D supplements. Your healthcare professional can advise you on whether you need to take Vitamin D supplements, and if so, how much to take.

Mechanism of action

Vitamin D promotes calcium absorption in the gut and maintains adequate serum calcium and phosphate concentrations to enable normal mineralization of bone and to prevent hypocalcemic tetany. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts . Vitamin D has a role in immune function, cell proliferation, and reduction of inflammation.

Vitamin D status is determined by the serum concentration of 25-hydroxyvitamin D (25(OH)D), which reflects vitamin D produced endogenously by sun exposure (80%) as well as dietary intake (20%). Vitamin D from the diet or skin synthesis is biologically inert and must undergo two successive metabolic conversions in the liver and kidney to become active. Vitamin D3 (cholecalciferol) is converted in the liver to 25-hydroxyvitamin D3 (25(OH)D3), also known as calcidiol, and then in the kidney to its active metabolite, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), also known as calcitriol.

The serum concentration of 1,25(OH)2D3 is tightly regulated by parathyroid hormone (PTH), calcium, and phosphorus. Vitamin D deficiency results in secondary hypocalcemia and hyperparathyroidism . Vitamin D intoxication results in hypercalcemia and calcification of soft tissues.

Vitamin D3 (cholecalciferol) is a fat-soluble vitamin that is produced in the skin when exposed to ultraviolet B (UVB) radiation from sunlight. Vitamin D3 can also be obtained from dietary sources, including fish, eggs, fortified milk and cereals, and supplements. Vitamin D3 is converted to 25-hydroxyvitamin D3 (calcidiol) in the liver, and then to 1,25-dihydroxyvitamin D3 (calcitriol) in the kidney.

Calcitriol is the active form of Vitamin D. It increases calcium absorption from the gut, promotes bone mineralization, and regulates calcium and phosphorus homeostasis to enable normal mineralization of bone. Vitamin D also has a role in immune function, cell proliferation, and reduction of inflammation.

Vitamin D deficiency can lead to Rickets in children and Osteomalacia in adults. Vitamin D intoxication can lead to hypercalcemia and calcification of soft tissues. Vitamin D supplements are available as tablets, capsules, liquids, and injectable solutions. Vitamin D3 is also available as an oral solution and a topical gel. Vitamin D2 (ergocalciferol) is available as an oral solution, a topical gel, and an injectable solution.