Bone, like all living tissue, needs an adequate supply of nutrients in order to grow and thrive. Calcium is one of these nutrients, but without vitamin D, the body cannot use calcium. When children are deficient in vitamin D, bones are soft and do not develop properly. In adults, vitamin D deficiency causes loss of bone density, leading eventually to osteoporosis, a condition in which bones fracture easily.
Bone Density Test
The best test to measure bone density is a DEXA scan. While you lie on a table, a machine scans your lower spine and hip, the sites where most osteoporotic fractures occur. No special preparation is involved. The test compares your bone density to that of a healthy 30-year old of the same gender and gives you a number, called a T-score. Between +1 and -1 indicates normal bone density; between -1 and -2.5 indicates osteopenia, a condition of low-bone density. Less than -2.5 indicates osteoporosis.
Forms of Vitamin D
Three forms of vitamin D exist, starting with cholecalciferol, also known as vitamin D-3. Your skin makes vitamin D-3, and it is found in supplements. From vitamin D-3, the body makes a pre-hormone called calcidiol. Calcidiol, also known as 25-hydroxyvitamin D, is the form that should be tested to determine D levels, which should be 50-80 ng/ml year-round. Next, the kidneys use calcidiol to make calcitriol, also known as 1,25-dihydroxyvitamin D. Calcitriol is the most potent steroid hormone in your body and the active form of vitamin D.
Vitamin D Recommendations
The National Institutes of Health advises from ages 1 through 70, people should get 600 IU of vitamin D daily through sunshine, food or supplements. People over 70 need 800. The upper limit for adults is considered to be 4,000 IU per day. Children under 12 months need 400 IU per day. Formula is supplemented with vitamin D. If you breast-feed, discuss with your doctor whether your baby may need vitamin D supplementation.
Sunshine and Vitamin D-3
The UVB radiation in sunlight interacts with a form of cholesterol in your skin to make vitamin D-3. Approximately five to 30 minutes of midday sun exposure twice a week is considered enough. In northern areas, you cannot get enough sun in winter to make vitamin D-3. Clouds and sunscreen reduce exposure; UVB radiation does not penetrate glass. Concerns about skin cancer can be another reason sun exposure is limited.
Food Sources and Supplements
The best food source of vitamin D is fatty fish. A 3-oz. serving of salmon contains 794 IU, while the same amount of mackerel contains 388 IU, and tuna contains 154 IU. One egg yolk contains 25 IU. Milk, soy milk, yogurt, orange juice and cereals are often fortified with vitamin D. Most multivitamins and many calcium supplements contain vitamin D-3, and if you are found to have low levels, your doctor can prescribe high doses of prescription vitamin D for a short period of time to bring your level up.
