What is vitamin D and what it does to human body?

Dr Shahid has summarized his six principles of health in a very simple form. Simplicity sometimes may not be politically correct. Well... What is wrong if people get the message and decide to live until 100 - 125 years and longer; without ever having to see any health care provider during all their long and healthy life? Moreover, you will live a life that is full of vigor, enthusiasm, happiness and contentment for 100-125 years and even longer.

What else can anyone ask for? Does it sound too good to be true?

Well... IT IS "too good" and IT IS "true".

Remember! Health is what "YOU" make of it. It is "YOUR" responsibility. Not your health care provider's.

Follow these six principles of Dr Shahid's Preventive Health. Or Healthy Life Style (HLS) and see the result for yourself. You be the judge. The best part of it is, "it won't cost you a penny". It is all free.

As they say,

"One ounce of prevention is better than two pounds of cure."

So here are the six principles of preventive healthy life style.

The basis (i.e. holistic prevention) of these six princioles is already discussed in previous blogs. Let us discuss these principles in detail.

The first principle of preventive health is a balanced diet. It consists of three parts:

1. Proteins, Fat & Carbohydrates in right proportion.
2. Vitamins, Minerals, fibers (VMF)
3. Water and Oxygen


We have completed an elaborate detail of the essential nutrients of balanced diet (Proteins, Fats and Carbohydrates) in previous blogs.

We have also given a brief description of #2 Vitamins, Minerals, fibers (VMF)

Let us describe vitamins in little more detail.

Very few people know what vitamins are and what is their real function in human body.

A brief history of vitamins was given in last blog. let us start with vitamins one by one in detail.

Vitamins are classified as either water-soluble or fat soluble. In humans there are 13 vitamins: 4 fat-soluble (A, D, E and K) and 9 water-soluble (8 B vitamins and vitamin C).

Fat-soluble vitamins

Fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids (fats). Because they are more likely to accumulate in the body, they are more likely to lead to hypervitaminosis than are water-soluble vitamins. Fat-soluble vitamin regulation is of of particular significance in cystic fibrosis.

1. vitamin A (Retinoid, retenol, carotinoid). Already discussed

2. Let us continue with next fat soluble vitamin, Vitamin D.

Vitamin D


Vitamin D is a group of fat-soluble prohormones (precursor of hormone), the two major forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol). Vitamin D3 is structurally similar to steroids such as testosterone, cholesterol, and cortisol (though vitamin D3 itself is a secosteroid).

The term vitamin D also refers to metabolites (products of metabolism) and other analogues of these substances. Vitamin D3 is produced in skin exposed to sunlight, specifically ultraviolet B radiation.

Vitamin D plays an important role in the maintenance of organ systems (body tissues).

1. Vitamin D regulates the calcium and phosphorus levels in the blood by promoting their absorption from food in the intestines, and by promoting re-absorption of calcium in the kidneys, which enables normal mineralization of bone and prevents hypocalcemic tetany. It is also needed for bone growth and bone remodeling by osteoblasts (bone forming tissue) and osteoclasts (bone removing tissue).

2. In the absence of vitamin K or with drugs (particularly blood thinners) that interfere with Vitamin K metabolism, Vitamin D can promote soft tissue calcification (depositing calcium in the tissue and making the soft tissue hard like bone).

3. It inhibits parathyroid hormone secretion from the parathyroid gland (four small glands in the neck located behind the thyroid gland.

4. Vitamin D affects the immune system by promoting phagocytosis (ability of the human cells, phaocytes to engulf and kill germs), anti-tumor activity, and immunomodulatory functions.


Vitamin D deficiency can result from:

1. From inadequate intake if balanced diet is not the main course of the meal.
2. Inadequate sunlight exposure.
3. Disorders that limit its absorption (such as Malabsorption Syndreom).
4. Conditions that impair conversion of vitamin D into active metabolites, such as liver or kidney disorders.
5. Rarely, by a number of hereditary disorders.

Deficiency results in impaired bone mineralization, and leads to bone softening diseases, rickets in children and osteomalacia in adults, and possibly contributes to osteoporosis.
However, sunlight exposure, to avoid deficiency, carries other risks, including ski cancer; this risk is avoided with dietary absorption, either through diet or as a dietary supplements

Vitamin D is a prohormone, meaning that it has no hormone activity itself, but is converted to the active hormone 1,25-D through a tightly regulated synthesis mechanism. Production of vitamin D in nature always appears to require the presence of some UV light; even vitamin D in foodstuffs is ultimately derived from organisms, from mushrooms to animals, which are not able to synthesize it except through the action of sunlight at some point in the synthetic chain. For example, fish contain vitamin D only because they ultimately exist on calories from ocean algae which synthesize vitamin D in shallow waters from the action of solar UV.

Production in the skin

The skin consists of two primary layers: the inner layer called the dermis, composed largely of connective tissue, and the outer, thinner epidermis. Vitamin D3 is produced photochemically in the skin from 7-dehydrocholesterol. The highest concentrations of 7-dehydrocholesterol are found in the epidermal layer of skin. Synthesis in the skin involves UVB radiation which effectively penetrates only the epidermal layers of skin.

A critical determinant of vitamin D3 production in the skin is the presence and concentration of melanin. Melanin functions as a light filter in the skin. Thus, individuals with higher skin melanin content will simply require more time in sunlight to produce the same amount of vitamin D as individuals with lower melanin content

Mechanism of action

Once vitamin D is produced in the skin or consumed in food, it is converted in the liver and kidney to its metabolically active form known as calcitriol. Following this conversion, calcitriol is released into the circulation and is then transported to various target organs.

The Vitamin D receptor (VDR) activation in the intestine, bone, kidney, and parathyroid gland cells leads to the maintenance of calcium and phosphorus levels in the blood (with the assistance of parathyroid hormone and calcitonin) and to the maintenance of bone content.

The VDR is known to be involved in cell proliferation and differentiation. Vitamin D also affects the immune system, and VDR are expressed in several white blood cells including monocytes and activated T and B cells.

Next we shall discuss the Nutritional aspect of Vitamin D, hypo and hyper vitaminosis D

For comment and questions please write to :

syedshahidmd@yahoo.com.au

Thanks