Vitamin D And Bone Health

Vitamin D is a fat-soluble vitamin that is very important for your bones and health in general. Your body needs vitamin D to process calcium, and without it, your body can't absorb any calcium which your bones need. Vitamin D isn't only important for your bones but can also lower your risk of cancer and infections and boost your mood. Your body produces its own vitamin D, but you can also get it from food and sunlight.

Vitamin D was always considered as a major contributor to the health of our bones. Recent research data suggest that even though this is correct, the benefits of additional supplementation with Vitamin D are only negligible.

Benefits of Vitamin D supplements for health are well advertised. The value of this small essential magic molecule was recognized well before it was actually identified. The compound was first noted as an important component of cod liver oil that could prevent the rickets disease in dogs. Initially, the molecule was mistakenly documented as Vitamin A, but later Professor Daniel Whistler and Francis Glisson acknowledged it as a distinct entity from vitamin A and renamed it as Vitamin D.

The key advances in our understanding of the structure, function, synthesis, mode of action, metabolism and health benefits of Vitamin D came into the light during the 19th century. Basically, vitamin D is a group of fat-soluble steroids, namely secosteroids, that help in improving the absorption of calcium and phosphate in the intestine. Till date, five different forms of vitamin D (D1-D5) have been identified and out of them most important one for humans are vitamins D2 (ergocalciferol) and D3 (cholecalciferol).

Vitamin D is plentiful in the food and also get produced in our body

The major sources of vitamin D are cod liver oil, fish, caviar (black and red), soy products (tofu and soy milk), fortified cereals, oysters, eggs, mushrooms, milk and milk products. However, unlike the other vitamins, Vitamin D can be autonomously produced in our own bodies (in the skin, specifically cholecalciferol) through direct exposure to the sun light. Frequent exposure of the skin to sunlight or ultraviolet irradiation (UV) results in the production of vitamin D from its dietary precursor 7-dehydrocholesterol. It is the skin that fulfills about 90 percent of total body needs of vitamin D in the form of Vitamin D3. In the commercial production, Vitamin D3 can also be synthesized through UV exposure, for instance by exposing the milk directly to the UV light.

Contrary to vitamin D3, Vitamin D2 is derived from a membrane sterol “ergosterol”. Ergosterol is mainly produced by yeasts, mushrooms, phytoplanktons and invertebrates and consequently get transformed into ergocalciferol (D2) in response to UV irradiation. However, it is not present in the vertebrates and green land plants. In the human body, cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2) are converted into calcidiol (25-hydroxycholecalciferol, or 25-hydroxyvitamin D3) and 25-hydroxyergocalciferol (25-hydroxyvitamin D2) and this entire event takes place inside the liver.

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Ergocalciferol and calcidiol are two specific stable vitamin D metabolites that are often used as serum markers to determine vitamin D status. The calcidiol is subsequently converted into calcitriol in the kidney. Calcitriol circulate in blood stream as a hormone and regulate the concentration of calcium and phosphate. This compound is known as the most biologically active form of vitamin D.

Vitamin D Supplements And Health Benefits

Studies during the past several decades authenticate an indispensible role of Vitamin D for human health. Vitamin D is required for adequate absorption of calcium and phosphate in our bones. It aids in proper development and remodeling of bone, cell to cell communication, control of cell growth, proper immune and neuromuscular functioning.

Some infrequent reports also suggest its association with pathophysiology of cancer, multiple sclerosis, rheumatoid arthritis, type 1 diabetes and cardiovascular disease. However, a lot of uncertainties are associated with health effects from vitamin D supplementation for these diseases.

The deficiency of vitamin D leads to a childhood disease of bones softening commonly known as “Rickets”. In this disease, bones fail to properly develop resulting in impaired bone mineralization and bone damage. In adults, vitamin D deficiency leads to “Osteomalacia” resulting in fragile bones, muscles weakness and bending of spines and legs. It has been observed that vitamin D deficiency decreases efficient calcium absorption and enhances the calcium loss from bones thereby increasing the risk for bone damages.

A large number of clinical data suggests that adequate vitamin D status enhance the bone mineral density and therefore protects against osteoporosis as well. Furthermore, inadequate levels of vitamin D can lead to an increased cancer risk, poor hair growth and weakened immune system.

Conversely, excess vitamin D can cause toxicity and allow the body to absorb too much calcium, leading to hypercalcemia. This result in an increase in urination and thirst, kidney stones, increased risk of heart attack and may lead to a syndrome of mental retardation and facial deformities in fetus during pregnancy. The toxicity of vitamin D is often caused by high doses of vitamin D supplementation (but not by sunlight exposure).

Current status of Vitamin D and Metabolic bone diseases

For decades, vitamin D has been associated with bone health and considered as an important source for preventing metabolic bone diseases and other complications caused by decreased bone density. It is well understood fact that vitamin D deficiency is associated with rickets in children and osteomalacia/osteoporosis in adults, as mentioned above. The deficiency is highly prevalent among general population in low-income countries and covers approximately 30-50% of total populations. In general, the Vitamin D insufficiency is present in every sector of the population but more prevalent among elderly people and young infants in most of the countries.

Initially, the importance of vitamin D for musculoskeletal health remained unrecognized and untreated. However, as the role of diet in the development of rickets was determined, increased emphasis was given for dietary intake of vitamin D to eradicate the disease. Low blood levels of vitamin D are also associated with increased mortality, particularly among elderly women. Apart from the low mineral bone density and osteoporosis, accumulating evidences have demonstrated that vitamin D deficiency may play an important role in infectious and chronic inflammatory diseases.

The benefits of Vitamin D supplementation for bone health appear to be marginal

A number of reports on vitamin D supplementation have reported variable results. These studies show inconsistent associations between bone mineral density and vitamin D status. The debate regarding an association between the vitamin D supplementation and the skeletal health benefits (such as prevention of bone fracture) still continues.

Recent analysis performed by researchers from the University of Auckland, New Zealand, puts a question mark to the current trend to provide certain groups of people with vitamin D supplements. The study focused mainly on published research data on the effects of vitamin D supplementation without co-administration of calcium on fracture prevention. This analysis compared the data from 23 clinical trials involving more than 4000 patients from numerous geographical locations.

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The result obtained in this study was rather surprising and suggests only negligible benefit of vitamin D supplementation on bone health. Although, at some skeletal sites small improvements in bone density were detected. It has been observed that statistically significant increase in bone density was localized only at the neck of the femur but not at the total hip region. Such a localized improvement is supposed to be artifactual, or a likelihood finding. In short, it has been suggested that single site localized effect on bone material density could not be considered as a reduction in fractures and makes very little clinical difference. In this respect, it has been suggested that we receive enough of this compound from the natural sources and thus make unnecessary the additional supplementation of vitamin D.

In short, research studies performed during last few years suggested that vitamin D supplementation provides only marginal benefits in the prevention of osteoporosis and recommend healthcare professionals to prescribe vitamin D supplements only to those people who have biochemical deficiency of this compound. Future studies are needed to analyze the effect of vitamin D supplements on bone density in terms of the dose given and the baseline vitamin D status to draw any effective conclusion.