July 29, 2011
Dear Mayo Clinic:
My niece, age 26, was recently found to have a very low vitamin D level on a blood test. She was advised to start taking a supplement immediately. Why would she be so low on vitamin D and what symptoms could this cause?
Vitamin D deficiency is common. Unlike most other vitamins, getting enough vitamin D doesn't depend solely on diet or supplements. Exposure to sunshine also contributes to a person's daily production of vitamin D. Not having enough vitamin D in the body can cause a variety of problems. Bone weakness is one of the most serious.
Not many foods naturally contain vitamin D, however, fatty fish (such as tuna and salmon) and eggs are a good source. Many dairy products, particularly milk and breakfast cereals, are fortified with vitamin D. Getting the proper amount of vitamin D takes more than dietary sources, though. It also requires sunlight, because ultraviolet light from the sun is necessary to start a chemical reaction in the skin that, after several complex steps, activates the body's ability to make vitamin D.
Because sunshine is necessary to ensure adequate vitamin D levels, people who have low sun exposure as a result of their lifestyle or due to the availability of sunlight where they live are at an increased risk of developing vitamin D deficiency. That risk is also increased in the elderly, as well as in anyone who has a gastrointestinal disorder that interferes with vitamin absorption into the bloodstream — such as celiac disease, Crohn's disease and cystic fibrosis — or in those who have undergone surgery that could limit the body's ability to absorb vitamin D, such as gastric bypass surgery.
Vitamin D has many roles in the human body. Among the most important is aiding in the body's absorption of calcium and phosphorus from the gastrointestinal tract, which helps to form and maintain strong bones. In addition, recent research has suggested that vitamin D may play a role in protecting the body from osteoporosis, high blood pressure, cancer and some autoimmune diseases.
As in your niece's situation, vitamin D deficiency is often diagnosed with a blood test, because a lack of vitamin D typically doesn't cause any obvious signs or symptoms until the deficiency is severe. If left untreated over time, vitamin D deficiency can lead to serious bone disorders. For example, severe and long-term vitamin D deficiency may result in rickets or osteomalacia. Both disorders are characterized by softening and weakening of the bones that can increase the likelihood of broken bones and lead to skeletal deformities.
In 2010, the Institute of Medicine increased the recommended daily requirement of vitamin D from 400 international units (IU) to 600 IU for most healthy adults and 800 IU for those age 71 and older. Based on that recommendation, some people — particularly those in groups at high risk for vitamin D deficiency — may need to take a supplement.
The good news for your niece is that increasing her vitamin D intake with the supplement her doctor recommended should bring her vitamin D level back into the appropriate range fairly rapidly. Long-term supplementation probably won't be necessary. In addition, unless her deficiency has been prolonged and severe, she is unlikely to experience any lasting health problems as a result of this vitamin D deficiency.
— Maria Collazo-Clavell, M.D., Endocrinology, Mayo Clinic, Rochester, Minn.