By Dena McDowell, MS, RD

Vitamin D has received a lot of press lately for its potential effects on weight management and decreasing cancer risk. Research is in its early stages and the anticancer mechanism has yet to be determined. However, making sure you have enough Vitamin D in your diet is an easy way to potentially reduce your risk of developing certain forms of cancer.

What is vitamin D?
Vitamin D is a fat soluble vitamin. It is found in certain foods and also can be produced in our bodies with direct exposure to sunlight. Food and sun sources of Vitamin D are unusable until the liver and kidneys help convert it into its active form. The active form of Vitamin D is known as the hormone 1,25 dihydroxycaliciferol and this active form is responsible for promoting calcium and phosphorus uptake from the intestines. Thus Vitamin D is responsible for helping create strong bones. Studies have also shown that Vitamin D may play a role in maintaining a healthy immune system.

Where is vitamin D found and how much is needed?
Other than sunlight (which is the greatest source of Vitamin D) this vitamin is found in fatty fish such as salmon, mackerel, tuna, sardines and code liver oil. Other sources include fortified milk, margarine, fortified breakfast cereals, egg yolks, and beef liver.

According to the International of Medicine there is not enough research to determine a recommended daily allowance for Vitamin D. Instead, Adequate Intake’s (AI’s) have been determined throughout the lifespan. The AI’s are expressed as International Units (IU’s) and are the following for each age group: birth to 50 years should have 200 IU a day, 51 to 70 should take in 400 IU’s each day and those 71 and older should take in 600 IU each day. The Upper Limit (UL) for adults for vitamin D through diet is 2000 IU a day. Doses exceeding the upper limit may cause nausea, vomiting, poor appetite, constipation and muscle weakness. Exceeding the UL in the long term may also cause an increase of calcium in the blood which can lead to heart arrhythmias.

Vitamin D and the cancer connection
Studies suggest that there is an inverse relationship with Vitamin D intake and cancer incidence. According to research adequate Vitamin D intake has proven protective against colon and rectal cancers in men. Those taking the highest amount of vitamin D had the lowest incidence of cancerous lesions in the colon as seen on colonoscopy. Retrospective research published in the Journal of Steroid Biochemistry and Molecular Biology looked at 18 different studies of Vitamin D and cancer risk and found the lowest colon cancer incidence in those taking high doses of Vitamin D. Those taking in 1000 IU of dietary Vitamin D had a 50 percent lower incidence of developing colon cancer. These studies were not controlled for sunlight exposure or family history. Another review study published in the American Journal of Public Health found that the higher the intake of Vitamin D was associated with lower incidences of breast, ovarian and colon cancer. Again the sunlight exposure and family histories were not analyzed. Researchers have not determined the mechanism of how Vitamin D lowers cancer risk therefore more research needs to be done. At this time spokespeople for the American Cancer Society believe that it is safe to take up to 1000 IU of vitamin D a day to decrease the risk of developing certain forms of cancer.

Conclusion
Vitamin D is a fat soluble vitamin that is found in limited food sources in the typical American diet. Sunlight is the best way to promote Vitamin D metabolism in the body. If you are limited to sun exposure and do not eat foods rich in Vitamin D a supplemental form of vitamin D is recommended. Calcium supplements often contain Vitamin D and together help promote good bone health. Until more conclusive evidence is created the IOM still recommends between 200-600 IU of vitamin D a day. If you have a family risk of colon, breast or ovarian cancer you may want to discuss taking higher amounts of Vitamin D with your physician.