Vitamin-D is a fat soluble vitamin. It is produced by the skin of the body from cholesterol on exposure to UV B rays of the sun. Because of which, it is also referred to as Sunshine Vitamin. Studies show that 5 to 30 minutes of exposure to sun, two times a week, based on the intensity of sun and age of the individual is sufficient to produce required Vitamin D by the human body.
The two important forms of this vitamin are Ergocalciferol (Vit.D2), synthesised by plants and Cholecalciferol (Vit.D3), synthesised by animals. Calcitriol, an active form of D3 is well known as steroid hormone, plays a vital role in regulating functions of many organ systems. Vitamin D helps in absorption of Calcium, Phosphate and Magnesium. Insufficient exposure to sun leads to deficiency. It causes Rickets (deformity of bones) in children and Osteomalacia (softening of bones) in adults. Elderly people, infants, house bound individuals, strict vegetarians and vegans, dark skinned people and those who live in continuous cloudy weather are more prone to Vitamin D deficiency. Research shows that its deficiency also affects diseases like cancer, asthma, cardiovascular diseases and disorders of immune system.
Vitamin D can be supplemented to overcome the deficiency. Food and Drug Administration of US recommends 400 units per day to an adult individual. Food sources of this vitamin are limited unlike other vitamins. Some of the rich sources are:
Plant sources: Alfalfa, raw white mushrooms, some fungi, fortified grain cereals, plant based milks like soy milk and rice milk and fortified orange juice.
Animal sources: Milk and other dairy products, whole egg, fish liver oil or cod liver oil, salt water fishes like Herring, Salmon, Sardines, Tunas Mackerel, Eel and beef liver.
A heavy dose of this vitamin leads to toxicity. So care should be taken as both deficiency and over dosage causes severe problems.