VITAMIN D AND HEALTH: BONES AND BEYOND
Vitamin D also called as vitamin D3 or ‘cholecalciferol’; is a fat-soluble vitamin. Human beings are dependent on the sun exposure to fulfill their needs of vitamin D. It is uv-B radiation that are being absorbed by 7-dehydrocholesterol present in the skin that aids in converting previtamin D3 to vitamin D3. Vitamin D is essential for the development of bones and also to enhance calcium and phosphorus uptake from the intestine. It assists in the oscillation of calcium ions between bone and blood. It is therefore vitamin D is essential component for all age groups; during infant to childhood stage it plays an essential role in bone development or else its deficiency results in bone deformation and rickets. In adults its deficiency results in softness of bone leading to osteomalacia. (Goldman, 2004).
Vitamin D3 once formed goes into circulation and is converted to 25 hydroxyvitamin D3 in liver, again released in circulation and subsequently converted to the active form of vitamin D, 1, 25- dihydroxyvitamin D3 in kidney. It is observed that Vitamin D deficiency remains unrecognized and therefore its insufficiency is taking a shape of epidemic among children and adults in United States.
Various research studies have been carried out throughout the world to conclude that vitamin D plays an imperative role not only for the bone health but also for various kinds of cancers, diseases related to heart, multiple sclerosis, in type I diabetes, also in various autoimmune diseases encompassing rheumatoid arthritis. Therefore, maintenance of suitable blood concentration of 25-hydroxyvitamin D (30 ng/ml) is very essential. As vitamin D is essential for enhancing intestinal calcium absorption, it’s appropriate level in the blood is also necessary for the formation of extrarenal 1?- hydroxylase which plays an imperative role in the formation of 1, 25- dihydroxyvitamin D3 (Holick, 2004).
Production and fate of Vitamin D
When an individual is exposed to sunlight previtamin D3 and also vitamin D3 forms photoproducts which are biologically inert. Vitamin D intake through diet or that formed in the skin with the help of sunlight come into the blood circulation, it reaches liver where it is metabolised to 25(OH)D3 by vitamin D 25-hydroxylase (25-OHase). 25(OH)D3 is again released in the circulation, it reaches kidney and get converted to 1,25(OH)2D3 in presence of enzyme 25(OH)D3 1 -hydroxylase (1-OHase). The renal production of active form of vitamin D is regulated by a variety of features encompassing serum phosphorus (Pi) and PTH. The active form of vitamin D (1,25(OH)2D) is now capable of managing the calcium metabolism. It is observed that the enzyme 25(OH)D 24-hydroxylase (24-OHase) enzyme which plays a crucial role in generating the active form of vitamin D, works on threshold mechanism to keep the check on the production of 1,25(OH)2D3 and if it is produced in higher quantity, the enzyme aids in the degradation of active vitamin D (Holick, 2004).
Further, it is also documented that 1,25(OH)2D can depress the activity of 1 -OHase, and the parathyroid hormone (PTH) can stimulate this activity. Many extrarenal tissues also express the 1 -OHase, these encompass tissues of bone osteoclasts, tissues of skin, macrophages, placenta, tissues of colon, tissues of brain, tissues of prostate, endothelial tissue, and glandular tissues of parathyroid. Extrarenal formation of 1,25(OH)2D3 might participate in the differentiation and proliferation of cell and also in immune response. Consequently, 1,25(OH)2D3 is essential for various physiological processes apart from its well-known function in calcium metabolism. In contrast to renal 1 -OHase, extrarenal 1 -OHase does not respond to stimulation by PTH. Furthermore, 1 -OHase may vary in expression with the physiologic state of a tissue as well as with disease progression (DeLuca, 2004).
Food incorporating Vitamin D
There are various resources of vitamin D, this encompass pure form of Cod liver oil, cooked form of Salmon, Mackerel, Tuna fish and Sardines canned in oil, sardines, margarine fortified, bran flakes, eggs, lamb liver. Fortified foods include milk and milk products especially cheese, orange juice and some breads and cereals (Vitamin D sources- Foods with Vitamin D).
As mentioned, the higher concentration of vitamin D influences the metabolic functions of the body, WHO has recommended intake dose of vitamin D by individuals belonging to different group. Up to the age of 50 years, during pregnancy and lactation the requirement is 200 IU/d, for the age group from 51-65 years it is 400 IU/D for the age of 65+ the requirement exceeds to 600 IU/d (Vitamin D sources- Foods with Vitamin D).
Considering the above data it is manifested that vitamin D is the most essential component for endorsing and preserving the health and vigor of bones as it directly affects the strength of bone in various skeletal and nonskeletal activities of the body encompassing cancers and depression (Lapp, 2009).
Symptoms of Vitamin D deficiency
Fall in plasma calcium and phosphate level, due to insufficient intestinal absorption, renders stimulation of parathyroid hormone (PTH) secretion to restore serum calcium and bone resorption.
In children, the deficient calcification of osteoid tissues result in bony deformities like bow leg, enlarged skull, spinal curvature, chest deformities and hepatosplenomegaly- characteristic features of Rickets. The reason is lack of appropriate bone tissue mineralization, causing soft bones and skeletal deformities. At-risk children are on prolonged exclusive breast feeding without supplementation of vitamin D. Additional risk factors includes vigorous use of sunscreens, and infants placed in daycares, with chances of sun exposure is reduced. Rickets is more prevalent in the children from Asia, Africa and Middle East (Davidson, 2002).
In adults decalcification and demineralization of bone leads to osteomalacia which is characterized by bone tenderness with pain and loss of bone density.
This disease is characterized by the aches and pains specifically in the lower back and thighs. Later on, it spreads to the arms and the rib cage. This pain does not radiate to other areas. It is accompanied by the local tenderness in bones. Another cardinal feature is the weakness of the proximal muscles. This represents as a difficulty in climbing up stairs and getting up from a squatting position.
Due to the deformation of bones, lordosis is a common representation. While walking, the patient shows a waddling gate. Pathological fractures due to weight gain may occur. Despite all these typical signs and symptoms, sometimes chronic fatigue may be the only representing sign (Eisman, 1988).
According to an estimate, about more than 25 million adults in United States alone are having or are at risk of developing this disease. This disease is most often associated with an inadequate calcium intake, therefore vitamin D is essential for reducing calcium absorption
Osteoporosis epitomizes reduction in mass of bone, also reduces microarchitectural framework of bone and thereby weakens the tissues of bone and amplifying the risk of fracture. The incidence of osteoporosis and fractures related with osteoporosis raise with age in both males and females, displaying a decline in bone mass with age.
Osteoporosis has emerged as a major health issue in developed nations. It is a condition that depicts frequent fractures, and is expected to influence more of females than males at some stage in their lives. As the age progresses bones become tender leading to osteoporosis in older adults, post menopausal women, non ambulatory individuals and individuals on chronic steroid therapy. The natural rhythm of the body allows a constant remodeling of the bones. In post menopausal women, this ratio is disturbed resulting in a greater amount of bone absorption rather than bone remodeling (Goldman, 2004).
Calcium and Vitamin D
Calcium 500- 1000 mg daily and vitamin D supplements 20µg daily have an established role in deterrence of elderly fractures, irrespective of whether or not BMD (Bone Mineral Density) values are reduced. This treatment is effective in reducing the danger of fractures related to hip fractures or other kind of fractures in community-living patients. (Davidson, 2002).
Reasons displaying insufficiency of vitamin D
Elevated pervasiveness of lactose intolerance causing undesirable effects with consumption of mild and dairy foods especially in African Americans. Reduced ingestion of vitamin D- equipped food products, predominantly liquefied milk, milk products cereals, because of changing attitude towards health concern and fat intake. Poor intake of calcium rich food encompassing poor intake of milk especially by the young women of reproductive age group thereby reduced concentration of vitamin D and calcium. Augmentation in the use of sun block lotions along with the diminished exposure to sun to avert the chances of skin cancer is also one of the reasons of vitamin D insufficiency. Human milk is meager in vitamin D, in the present era there is enhanced predominance in the duration of breast- feeding ensuing insufficient intake of vitamin D. thus causing low circulation of 25-hydroxyvitamin D concentrations among women. Due to air pollution in industrial areas, the exposure to uv- radiation is reduced and also the poor dietary habits and availability of vitamin D equipped food makes the individual a victim of vitamin D deficiency. In rare cases impaired absorption, enhances body requirement of vitamin D۔