While calcium gets most of the press when it comes to bone health, vitamin D is also essential for proper bone growth and repair. In the body, vitamin D and calcium work in concert to maintain skeletal integrity. Deficiencies in vitamin D can upset this balance and lead to bone problems over time.
Types
Vitamin D comes in a few different forms. Vitamin D2, or ergocalciferol, comes from plants and yeast. Vitamin D3, or cholecalciferol, is the form synthesized by the body in response to sunlight and is also found in animal products and fortified foods. Both vitamin D2 and D3 must be converted into another form of vitamin D, calcitriol, before they can be used.
Activity
Calcitriol, the active form of vitamin D, operates in the intestines to assist in the absorption of calcium and phosphorus from food. Calcitrol also operates in the kidneys to pull calcium back into the bloodstream that was filtered out via the kidneys. Vitamin D shuttles this serum calcium into growing bones. When blood levels of calcium get too low, calcitriol also can pull calcium from the bones.
Deficiency
Severe vitamin D deficiency is rare, but the main symptoms involve the bones. When the body is deficient in vitamin D, the calcium balance in the body becomes unstable and the parathyroid gland produces hormones that pull calcium out of the bones. In the childhood form -- rickets -- calcium loss causes developmental problems and deformities of the skeleton. In adults, osteomalacia causes the bones to soften as they lose calcium and phosphorus. Milder forms of vitamin D deficiency can accelerate or allow the development of osteoporosis.
Levels
When blood serum levels of vitamin D fall below 30 ng/mL, this mild deficiency can contribute to bone-density loss and possible osteoporosis. Supplementation of 600 to 800 IU of vitamin D3 each day may have a protective effect on the bones, explains the Linus Pauling Institute at Oregon State University. Vitamin D3 supplementation is linked to a lower incidence of fractures and a slowing of bone density loss. Vitamin D3 appears to be more effective than D2 at protecting bone health.
Considerations
Older individuals, the age group most prone to bone problems such as osteoporosis, may have a higher need for vitamin D than younger people. Merck Manuals suggests that older people may need as much as 2,000 IU of this vitamin each day and that current guidelines of 400 IU daily may be insufficient for this age group. Vitamin D supplementation alone is insufficient to protect and promote bone health; calcium intake must also be adequate.
Member Comments