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Vitamin D: More than just a vitamin

Rohini Diniz

Vitamin D is a fat-soluble vitamin that is also called ‘Sunshine Vitamin’ because it is synthesised in the body in the presence of sunlight. Vitamin D is not just a vitamin that we eat, but also a hormone that our bodies produce. Adequate vitamin D is crucial at every stage of our lives, from childhood to old age.

Vitamin D has very critical metabolic functions in the body as it is needed for the absorption of calcium and phosphorus and aids the process of bone mineralisation. Evidence from newer research studies has shown that vitamin D has a far wider role to play, not only in musculoskeletal health, but also for in preventing chronic diseases. Although more research is needed to determine the beneficial effects of vitamin D in these areas studies have shown that vitamin D helps reduce the risk of developing diabetes, cardiovascular disease, certain types of cancers, depression, autoimmune disorders, allergy and infectious diseases such as tuberculosis, asthma and even frailty.

How does the body use vitamin D? Vitamin D is a metabolically inactive compound that requires to be transformed into several active metabolites in the liver and kidney. The skin contains 7-dehydrocholesterol, a cholesterol derivative, which in the presence of sunlight gets converted into vitamin D-3 or cholecalciferol. Cholecalciferol obtained from food and from the conversion of 7-dehydrocholesterol is then converted into 25 hydroxy vitamin D-3 in the liver. This 25 hydroxy vitamin D-3 is then converted in the kidney into the metabolically active form 1, 25 dihydroxy vitamin D-3 or calcitriol.

Calcitriol functions as a hormone as it increases the intestinal absorption of calcium and phosphate, promotes the deposition of calcium in the bones, decreases levels of parathyroid hormone (PTH) as well as decreases the loss of calcium from the bones.

During the last few years, vitamin D as caught the attention of the medical fraternity on account of the rise in vitamin D deficiency disorders in all age groups all over the world, even in the tropics where sunshine is abundant. It has been estimated that around one billion people all over the world have inadequate levels of vitamin D in their blood. Vitamin D deficiency is now being recognised as a pandemic with a myriad of health consequences.

Lifestyle changes such as inadequate exposure to the sun on account of long working hours indoors during the day, travel by vehicles instead of walking, the use of sunscreens and not consuming enough of vitamin D rich foods are some of the factors that are contributing to the rise in vitamin D deficiency.

As compared to people with fair skins, those who have darker skin (people of African, African-Caribbean and South Asian origin) are at an increased risk of being deficient in vitamin D because melanin acts as a filter to ultraviolet B (UVB) radiation and reduces the amount of vitamin D that the body makes in the skin.

Vitamin D deficiency affects the absorption of calcium in the body which in turn affects the bones, teeth and muscles. In milder forms, vitamin D deficiency leads to body aches, back ache and joint pain that do not respond to treatment. Severe deficiency leads to rickets (softening and weakening of bones) in children and osteomalacia in adults. The symptoms of osteomalacia include muscle weakness and widespread bone pain, especially in the pelvic region and fractures that occur without a real injury Studies have shown that vitamin D deficiency may have a role in causing osteoporosis in older people.

The best way to know a person’s vitamin D status is to have a yearly 25 hydroxy Vitamin D-3 test done. Since this is the storage form of vitamin D it correlates best with deficiency symptoms.

For most individuals, vitamin D requirements are primarily met from the synthesis of vitamin D in the skin in the presence of sunlight.  Very few foods naturally contain vitamin D. Milk and milk products, egg yolk, fatty fish and fish liver oils and vitamin D fortified foods are good dietary sources of vitamin D. Ideally a balanced diet coupled with adequate exposure to sunshine should prevent vitamin D deficiency. A daily exposure to the sun around mid-day (11 a.m. to 3 p.m.) for half an hour is recommended. Those who do not get adequate exposure to the sun should consider taking supplements of vitamin D in consultation with a doctor.


The writer is a consultant nutritionist with 18 years of experience, practising at Panaji and can be contacted on rohinidiniz@gmail.com

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