What is Vitamin D?
Vitamin D is a fat soluble vitamin essential for calcium and phosphate metabolism. Vitamin D plays an integral in development of bone and muscles. The skeletal health consequences of vitamin D deficiency (calcium malabsorption and skeletal fragility) have long been recognized. More recently it has become appreciated that low vitamin D status leads to muscle weakness, falls, and potentially a multitude of nonskeletal morbidities.
Prevalence of Vitamin D deficiency
Vitamin D deficiency is a world-wide epidemic, with recent estimates indicating greater than 50% of the global population is at risk.
A high prevalence of vitamin D deficiency has been found across all age groups in all populations studied in countries around the globe.
Even those who are otherwise healthy are not immune to deficiency.
Manifestations of Vitamin D deficiency
Vitamin D deficiency can remain asymptomatic and may be picked up only on routine testing.
Severe vitamin D deficiency is however known to cause several bone diseases including:
- Rickets, a childhood disease characterized by impeded growth, and deformity, of the long bones. The earliest sign of subclinical vitamin D deficiency is Craniotabes, abnormal softening or thinning of the skull.
- Osteomalacia, a bone-thinning disorder that occurs exclusively in adults and is characterized by proximal muscle weakness and bone fragility.
- Osteoporosis, a condition characterized by reduced bone mineral density and increased bone fragility.
- Muscle aches and weakness (in particular proximal limb girdle).
Sunlight and Vitamin D
Humans make 90 percent of vitamin D naturally from sunlight exposure to skin – specifically, from ultraviolet B exposure to the skin, which naturally initiates the conversion of cholesterol in the skin to vitamin D3.
Sunlight is the best and only natural source of vitamin D. Unlike dietary or supplementary vitamin D, when you get your ‘D’ from sunshine your body takes what it needs, and de-metabolizes any extra. That’s critical – as vitamin D experts and many health groups now advocate 1,000 to 2,000 IU of vitamin D daily – five to ten times the old recommendations. Because too much ‘D’ from dietary supplements may cause the body to over-process calcium, nobody really knows for sure how much supplementary vitamin D is safe. On the other hand, sunlight-induced vitamin D doesn’t have that problem.
The amount of vitamin D produced in the skin depends on the intensity of the UVB in the sun and many other factors. Darker-skinned individuals may need 5-10 times more exposure than a fair-skinned person to make the same amount of vitamin D.
Treatment of Vitamin D Deficiency
The need for treating vitamin D deficiency arises either when patients present with musculoskeletal symptoms attributable to hypovitaminosis D or when screening of individuals at high risk reveals the presence of vitamin D deficiency, as defined by serum 25(OH)D levels <20 ng/ml. The recommended dietary intakes of vitamin D vary with age and physiological state. The recommended daily intake ranges from 400 IU in infants, 600 IU in children and adults and 800 IU in those over 70 years of age, though higher doses varying from 1000 IU per day in infants and children to 1500–200 IU per day in adults and the elderly being required to raise 25(OH)D levels to 30 ng/ml (the level of sufficiency). The recommended dose increases 2- to 3-fold when the individual is on anti-convulsant drugs, glucocortiocids, anti fungal agents and anti-retroviral therapy.
Correction of vitamin D deficiency requires higher daily doses of vitamin D, ranging from 2000 IU for those <1 year of age, 4000 IU for children between 1–18 years of age, and 10,000 units for adults. These doses can either be delivered on a daily basis or an equivalent dose calculated and provided on weekly basis. For infants and children, both the daily dose (2000 IU /day) or a weekly calculated dose (50,000 IU per week for 6 weeks followed by 1500–200 units per day) are acceptable. In adults, the commonest strategy is to give 50,000 units per week for 8 weeks followed by 2000 IU per day or an equivalent weekly or monthly dose.
In the elderly additional anticipated benefits include fall prevention and fracture risk reduction. vitamin D therapy targeting serum 25(OH)D levels ≧ 60 nmol/l is associated with fall prevention, while levels between 66–74 nmol/l appear to be required to reduce the risk of non-vertebral and hip fractures.