Vitamin D is a fat-soluble vitamin needed for calcium absorption, bone growth and a healthy immune system. It is found in few foods, including fatty fish, fish liver oils, beef liver, egg yolk, cheese and fortified foods. Humans can also synthesise vitamin D when their skin is exposed to the ultraviolet rays in sunlight. A vitamin D deficiency increases the risk of rickets in children and osteomalacia (soft bones) in adults.
Vitamin D Supplements, D2 and D3
The recommended dietary allowance (RDA) of vitamin D with minimal sun exposure is 600 IU (15 mcg) for males and females aged 1 to 70 years, according to the Office of Dietary Supplements. This is the average amount needed daily to meet vitamin D requirements and maintain calcium metabolism for most people.
If getting enough vitamin D from natural sources is a problem, dietary supplements are an option. Vitamin D is added to supplements and fortified foods in the form of vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). Although slightly different in their chemical composition, vitamins D2 and D3 have a similar level of effectiveness and both can be used to treat rickets.
Vitamin D in breast milk is not usually concentrated enough to meet vitamin D requirements. The American Academy of Pediatrics suggests breast fed infants are supplemented with 400 IU (10 mcg) of vitamin D daily until they are weaned and consuming at least 1,000 mL daily of vitamin D-fortified milk. The same is advised for non-breast fed infants consuming less than 1,000 mL per day of vitamin D-fortified milk. People with limited sun exposure, dark skin, fat malabsorption and obesity may also need vitamin D supplements to meet their daily vitamin D requirements.
Vitamin D Toxicity and Hypercalcaemia
A prolonged vitamin D intake of 10,000 to 40,000 IU per day or a blood concentration of more than 500 nmol/L is potentially toxic. Vitamin D toxicity is likely to occur from taking high levels of vitamin D in the form of supplements, rather than consuming foods high in vitamin D. Excessive sunlight exposure does not cause vitamin D toxicity.
The tolerable upper intake level, or maximum daily intake of vitamin D for adults and children aged over 9 years is 4,000 IU (100 mcg). An intake of vitamin D above the tolerable upper intake level or a vitamin D blood concentration above 125 nmol/L may increase the risk of adverse health effects.
Vitamin D toxicity may cause hypercalcaemia (high blood calcium levels) and bone loss, which can be serious and requires medical intervention. Damage to kidneys and other organs is possible. Symptoms of hypercalcaemia may include weight loss, loss of appetite, nausea, vomiting and polyuria (excessive urination). Excessive vitamin D intake may also be linked with some types of cancer, cardiovascular problems and bone fractures in the elderly.
Adequate vitamin D intake is vital for good health and the prevention of some diseases, although it can be toxic at high levels. A vitamin D deficiency can also have adverse health effects. For more information, read How to Avoid Symptoms of Vitamin D Deficiency.
Resources:
American Academy of Pediatrics. "Vitamin D and Your Baby" (Accessed 4th February 2011).
Mayo Clinic. "Vitamin D" (Accessed 4th February 2011).
MedlinePlus. "Vitamin D" (Accessed 4th February 2011).
Office of Dietary Supplements. "Vitamin D" (Accessed 4th February 2011).
Sharon Kirby - Sharon is a freelance health writer and contributes to various print and online publications. Writing credits include Nursing Times, Good ...
