Vitamin D (VITD) is important in bone health, skeletal muscle growth, inflammatory modulation, immune and cardiopulmonary function. VITD can also interact with extraskeletal tissues to modulate injury recovery and influence of the risk of infections. It is estimated that 1 billion people in the world currently have VITD deficiency and that number is on the rise. The major cause for the VITD deficiency is the lack of awareness in the population that sun exposure is the main source of vitamin D. In relation to food sources of VITD, it is difficult to obtain vitamin D through the diet because very few foods naturally contain the vitamin, exceptions being eggs, cheese and fatty fish such as salmon, sardines, herring.
How is Vitamin D Metabolized?
Vitamin D is an organic compound in food needed in small amounts for growth and good health but the human requirement can actually be met entirely through synthesis in the skin upon exposure to sunlight. The ultraviolet-B (UVB) radiation in sunlight converts to D3 and the newly synthesized vitamin D (as well as vitamin D obtained from the diet) is escorted to the liver. In the liver, vitamin D is rapidly converted to 25(OH)D, the main storage form. Further activation in the kidney is driven by parathyroid hormone (PTH) when blood calcium and/or phosphate concentrations fall below the normal range.
Benefits of Vitamin D
Sufficient levels of Vitamin D provide multiple musculoskeletal benefits such as: increased muscle protein synthesis, ATP concentration, strength, jump height and velocity, exercise capacity, physical performance, decrease muscle protein degeneration and reverse myalgias. It is also well known that vitamin D plays an important role in bone health, fracture prevention and reducing the risk and impact of diabetes, multiple sclerosis, certain cancers, cardiovascular diseases and hypertension, cerebrovascular diseases, infectious diseases, asthma, depression, and other autoimmune and chronic inflammatory disorders.
How much Vitamin D do you need?
In order to properly assess levels of Vitamin D, blood levels of total 25-hydroxy vitamin D (25(OH)D) must be taken. There are studies which suggest that a value of 25(OH)D >30 ng/mL should be considered as acceptable for maintaining bone health and reducing the risk of fracture in healthy young people and adults, while others suggest that necessary levels should be set at >40 ng/mL. 25(OH)D levels above 40 ng/mL are required for fracture prevention, including stress fractures. Optimal musculoskeletal benefits occur at 25(OH)D levels above the current definition of sufficiency (> 30 ng/mL) with no reported sports health benefits above 50 ng/mL. The Institute of Medicine recommended dietary allowance (RDA) of vitamin D for the US and Canada is 600 IU for children and adults under 70 years of age and 800 IU for those over 70 years old. It is important that you discuss this with your primary care provider prior to taking any Vitamin D supplements.
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