It is fat-soluble vitamin D that is primarily responsible for maintaining bone health. Research has shown that vitamin D provides protection from osteoporosis, according to the MayoClinic.com. When your vitamin D level becomes inadequate, an excessive amount of calcium is absorbed, increasing parathyroid hormone secretion. Increased parathyroid hormone secretion causes increased bone resorption, which weakens your bones and elevates your risk of fracture.
Sources
Vitamin D does not have to come from the diet, according to Janice Thompson, Ph.D., author of "Nutrition: An Applied Approach." Your body synthesizes vitamin D using energy from exposure to sunlight. In fact, as little as 10 minutes of sun exposure a day is thought to be sufficient to prevent vitamin D deficiencies, according to the MayoClinic.com. However, if people do not receive an adequate amount of sunlight each day, they must consume vitamin D in their diet or take supplements.
Most foods contain very little vitamin D, according to Dr. Thompson. However, many foods, such as cereals, dairy products and juices are fortified with vitamin D. Other sources include cod liver oil, salmon, mackerel, sardines and egg yolks.
Mechanism
Vitamin D, parathyroid hormone and calcitonin work in unison to regulate blood calcium levels to maintain bone health. Together they regulate the absorption of calcium and phosphorus from the small intestine -- they absorb more when the body requires greater amounts, they absorb less when the body's needs are lower.
Additionally, vitamin D, parathyroid hormone and calcitonin decrease or increase blood calcium levels via the kidney, causing it to excrete more or less calcium in the urine to meet the demands of the body. Lastly, vitamin D and parathyroid hormone work together to stimulate osteoclasts, which break down bone when greater amounts of calcium are needed in the body.
Dietary Recommendations
There's currently no recommended dietary allowance, or RDA, for vitamin D. However, the adequate intake, or AI, for vitamin D for men and women aged 19 to 50 years is 5 µg/day, while the AI for men and women age 50 to 70 years is 10 µg/day, and 15 µg/day for those over the age of 70 years. These AI dosages, listed by MayoClinic.com, are based on the assumption that individuals do not get adequate sun exposure.
Deficiency
Inadequate production via sun exposure or reduced dietary intake of vitamin D primarily results in a loss of bone mass, according to Dr. Thompson. Vitamin D deficiency causes adults to experience bone pain, muscle weakness and osteomalacia. Osteomalacia means "soft bones," and is an impairment of bone mineralization, whereby bones are weak and prone to fracture, according to the MayoClinic.com.
The reduction of bone mass associated with vitamin D deficiency can also lead to osteoporosis. Osteoporosis is characterized as a disease in which bone mass is low due to the deterioration of bone tissue, according to Hopkins Medicine. People with osteoporosis have fragile, weak bones. Hopkins Medicine states their risk of fracture increases substantially, especially in their wrists and hips.
References
- MayoClinic.con: Vitamin D
- Hopkins Medicine: Chapter 27 -- Osteoporosis and Osteomalacia
- "Nutrition: An Applied Approach. MyPyramid Edition;" Janice Thompson and Melinda Manore; 2006
