Vitamin D is a fat-soluble vitamin. A fat-soluble vitamin means it can be stored by the body and released when needed. Vitamin D is most commonly produced in the skin as cholecalciferol (D3). There is different forms of Vitamin D, but the most important form is D3. It can be formed naturally from sunlight exposure as the UVB rays enables the body produce Vitamin D from cholesterol. Vitamin D can also be found in found sources such as dairy, oily fish, egg yolk, and cod liver oil.
Vitamin D has many benefits including keeping your immune system strong, and maintaining bone health. It has been shown that taking vitamin D supplements may reduce the risk of respiratory infections.
The amount of Vitamin D required depends on several factors including skin colour and UV exposure (different environments). For example, people with fairer skin need less sunlight exposure than those with darker skin. Typical RDA for those aged 1-70 years is 600 IU (international units/day)
What are some of the common causes?
Causes of low Vitamin D levels can include inadequate sunlight exposure, low dietary intake of Vitamin D, conditions that affect the absorption of vitamin D, obesity, darker skin tone.
What are some of the symptoms of Vitamin D deficiency?
Deficiencies can lead to fragile weak bones, possible fractures, back pain, pain in bones, Rickets or Osteomalacia, symptoms of fatigue and tiredness, or a depressed mood.
The Science bit
There are two forms of Vitamin D; Vitamin D2 (Ergosterol) found in plants, and Provitamin D3 (7-dehydrocholesterol) formed in the skin. Tring to obtain the right amount of UV exposure can be a balancing act. Too little can lead to Vitamin D deficiency while too much UV exposure can increase the risk for skin cancer and can speed up the aging process.
Vitamin D plays an important role in the absorption of calcium and phosphorus. Vitamin D in the presence of UVB light interacts with 7-dehydrocholesterol in the skin to make vitamin D3. Vitamin D derived from either our skin or from food starts as an inactive form. It first travels to the liver to and becomes the circulating form of Vitamin D (calcifediol (25-OH D)). It then travels to the kidney where it is transformed in the active form called calcitriol which is more effective than circulating Vitamin D.
Calcium absorption requires calcitriol. The role of calcitriol is that it is involved in increasing the expression of calcium transporters on the surface of enterocytes to allow the uptake of more calcium. It also increases the amount the protein calbindin in the cytosol which bind the calcium and allows calcium to be moved through the enterocyte and into the blood though the ATP dependant calcium pump. The activity of the ATP dependant calcium pump is also increased by the action of calcitriol.