Vitamin D, also known as the sunshine vitamin, unlike other vitamins, is a hormone and all the body cells have receptors for it. This vitamin D is biologically inert and undergoes two processes in the body for activation. The first step occurs in the liver, which converts vitamin D to 25-hydroxyvitamin D (precursor to the active form of vitamin D). The kidney converts 25-hydroxyvitamin D to 1,25-hydroxyvitamin D, the active form of vitamin D in the body.
Vitamin D importance
Vitamin D is vital for maintaining health. The most important role of vitamin D in our body is the absorption of calcium from the gut. It also maintains adequate serum levels of phosphate, magnesium, and calcium that aids in normal mineralization of bone. Balance in the functioning of osteoblasts (cells that are responsible for the formation of bones) and osteoclasts (responsible for the breakdown of bones) is important for bone growth. Vitamin D aids in bone remodeling by influencing the activity of osteoblasts and osteoclasts. Vitamin D deficiency can result in thin and brittle bones. Moreover, vitamin D deficiency can cause rickets in children and osteomalacia (softening of the bones) in adults. It also protects the elderly from osteoporosis (reduction in bone mass).
Other roles of vitamin D in the body include lowering of inflammation, maintaining immune function, modulation of cell growth, and regulating apoptosis (programmed cell death).
Important facts about vitamin D
Serum level of 25-hydroxyvitamin D is the best indicator of vitamin D. Below-mentioned are normal and clinically abnormal ranges of 25-hydroxyvitamin D
- ≥30 µg/mL is considered adequate for bone and overall health
- 20 to 29 µg/mL is classified as insufficiency
- 10 to 19 µg/mL is classified as a mild deficiency
- <9 µg/mL is moderate-to-severe deficiency
- <5 µg/mL is severe deficiency
Sources of vitamin D
- Sun exposure: It is the most important source of vitamin D. Ultraviolet (UV) B radiation penetrates the uncovered skin and converts cutaneous cholesterol (7-dehydrocholesterol) to pre-vitamin D3, which is later converted to the active form in the kidneys and liver. Researchers recommend 5-30 minutes of sun exposure from 10 AM to 3 PM, twice a week without sunscreen on arms, legs, face, or back.
- Dietary sources: Several foods contain vitamin D like fatty fish (such as mackerel, tuna, and salmon), fish liver oils, cheese, beef liver, and egg yolk.
Causes of vitamin D deficiency:
Vitamin D deficiency is generally a result of dietary inadequacy, increased requirement, impaired use or absorption, or increased secretion. Some of the reasons include limited exposure to sunlight, kidney disorders (as kidneys won’t be able to convert vitamin D to its active form), and gut disorders (as it would cause abnormal absorption of vitamin D from the digestive tract). Furthermore, vitamin D deficiency is associated with lactose intolerance, veganism, and milk allergy.
Disorders associated with vitamin D deficiency
As mentioned above vitamin D benefits bone growth and various other functions of the body. Some of the disorders associated with vitamin D deficiency are as follows:
- Recurrent illnesses
- Bone and back pain
- Impaired wound healing
- Easy fatigue
- Bone loss
- Frequent fractures
- Soft and brittle bones
Risks associated with higher levels of vitamin D
Higher than normal level of vitamin D can cause certain symptoms like increased frequency of urine, irregular heartbeat, weight loss, and loss of appetite. It can also increase levels of calcium that can cause vascular and tissue calcification causing damage to the heart, blood vessels, and kidneys.