a. is usually not necessary as it is found in most foods
b. causes rickets, a bone disease
c. may protect against cancer
d. all of the above
e. none of the above.
The correct answer is C. Vitamin D has has received much attention recently. Several studies have reported an array of health benefits associated with vitamin D in children and in adults, possibly protecting against cardiovascular disease, certain cancers, and immune system disorders such as rheumatoid arthritis. These data have generated debate over the daily amount of vitamin D that should be recommended.
The current recommendation is 200 to 600 international units (IU) daily, depending on age. New data has emerged to question this guideline. There are very few food sources of vitamin D, namely fatty fish and eggs. Most of our vitamin D is synthesized in our skin through a process that requires sunlight. However, due to more sedentary lifestyles such as long working hours, web surfing, and playing video games, and heeding advice to avoid the sun to prevent skin cancer the level of vitamin D may be lower than our body requires. Some even suggest a worldwide pandemic of vitamin D deficiency.
It is well established that vitamin D deficiency causes rickets, a bone disease which usually affects children, in which the bones become very soft. See Dr. Janesta Noland's post on this blog regarding new vitamin D recommendations for children.
Additional benefits have been suggested for adults. In one study, vitamin D supplementation of 800 IU daily was associated with a decreased risk of colon cancer. This was shown to occur as a result of the expression of Bax - a protein that promotes the killing of damaged cells. In three meta-analysis observational studies, a serum 25-hydroxyvitamin D level of 30 ng/ml (75 nmol/L) or higher was associated with at least a 50% lower risk of breast cancer. As a result it has been suggested that women should be checked annually for vitamin D level to better identify their risk of breast cancer. A study funded by the National Institute of Health showed that women who took 1100 IU per day of vitamin D for 4 years reduced their risk of breast cancer by 60 percent.
Bottom line is that although it is not yet an official recommendation, based on recent studies, there may be a benefit to taking between 1000-2000 IU per day of vitamin D.
References: see above links. Am. J. Clinical Nutrition, 2007; 85:1586-91