Vitamin D is a group of fat-soluble secosteroids. Two main forms are active in the human body: vitamin D2 and D3. D2 comes mainly from plant sources, while vitamin D3 is synthesised in our skin under the influence of the sun’s ultraviolet (UVB) rays and is obtained from animal sources.
How it is converted inside the body
The vitamin D we get from the sun or food cannot work directly. It is converted in the liver to “calcidiol” and then in the kidneys to “calcitriol,” or active vitamin D. It is this active form that communicates with the body’s cells.
The many roles of vitamin D in the body
- Protecting bones and the skeletal system. Vitamin D’s main job is to help absorb calcium and phosphorus from the gut. Without these, bone mineralisation is not possible. In children, deficiency causes rickets, which softens and bends the bones; in adults, it raises the risk of osteomalacia, or bone pain, and osteoporosis, or bone loss.
- Immune system. Vitamin D activates our white blood cells (T-cells and macrophages). It plays a major role in preventing autoimmune diseases such as type 1 diabetes, multiple sclerosis and rheumatoid arthritis. Recent research has shown it to be effective in reducing the severity of various respiratory infections, including COVID-19.
- Muscle function and balance. Vitamin D works directly through cell receptors to build muscle strength. In older people, one of the main causes of bone fractures is losing balance and falling; adequate vitamin D improves muscle coordination and reduces this risk.
- Mental health and depression. The parts of the brain that control mood have vitamin D receptors. Sunlight plays an immense role in overcoming Seasonal Affective Disorder and ordinary depression.
- Heart health and blood-pressure control. It reduces inflammation of the blood vessels and helps lower high blood pressure by regulating the renin-angiotensin system.
- Stronger teeth. Research suggests vitamin D supplements prevent tooth decay in children and adults; it improves the minerals in teeth and prevents decay.
- Excessive fatigue. With a vitamin D deficiency, the body can feel constantly tired and weak even after adequate rest.
- Excessive hair loss can also be a sign of vitamin D deficiency.
- Slow wound healing. With a vitamin D deficiency, wounds from injury or surgery take longer than normal to heal.
- Helps with weight loss. Vitamin D-rich foods help control appetite, making weight loss easier. They also boost energy and reduce fatigue, which helps a person stay physically active and manage their weight.
Causes of vitamin D deficiency
Vitamin D deficiency does not depend on personal diet alone; it is a multi-dimensional problem. Its three main causes are analysed below.
A. Geographic and environmental factors
- Latitude: The further north or south of the equator one goes, the more obliquely the sun’s rays fall on the earth. As a result, the atmosphere’s ozone layer absorbs the ultraviolet (UVB) rays and the skin cannot make enough vitamin D.
- Seasonal change: In winter the days are shorter and people wear more clothes. Overcast skies or fog also block UVB rays.
- Air pollution: In industrial areas or densely populated cities (such as Dhaka or Delhi), airborne particles and smog filter the sunlight, so the rays the skin needs cannot reach it.
B. Social and lifestyle factors
- Indoor life: In modern urban life, people spend most of the day in offices, homes or shopping malls. A lack of playgrounds for children and addiction to online games deprive them of sunlight.
- Clothing and culture: Wearing clothes that cover the body for religious or cultural reasons reduces the skin’s exposure to light.
- Use of sunscreen: Sunscreen of SPF 30 or higher reduces the skin’s ability to make vitamin D by about 95-98 percent.
- Food security and habits: A lack of nutritious food in developing countries and an excess of processed food in the developed world both keep people away from adequate sources of vitamin D.
C. Biological and genetic factors
- Skin colour: Melanin is a natural sunblock. People with darker skin need three to five times longer in the sun than fair-skinned people to make vitamin D.
- Obesity: Vitamin D is fat-soluble. Excess body fat traps vitamin D in the fat cells (sequestration) and keeps it from entering the bloodstream.
- Age: As people age, a compound in the skin called 7-dehydrocholesterol — the main raw material for making vitamin D — declines.
- Genetic mutation: Some people have a defect in the Vitamin D Receptor (VDR) gene, so the body cannot take up vitamin D even when there is enough of it.
বাংলায় মূল প্রতিবেদন পড়ুন · Read the original Bengali report