Vitamin D and Cancer | Anchorage Radiation Therapy

As word about vitamin D and cancer prevention makes the news, here’s what you need to know about the latest vitamin to hit the big time.

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

Vitamin D is a fat-soluble vitamin found in certain foods; it can also be produced in our bodies with direct exposure to sunlight. Food and sun sources of vitamin D are unusable until the liver and the kidneys help convert it into its active form. The active form of vitamin D is known as the hormone 1,25-dihydroxycalciferol, 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, and studies have shown that it may also 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 cod-liver oil. Other sources include fortified milk, margarine, fortified breakfast cereals, egg yolks, and beef liver.

According to the Institute of Medicine, there is not enough research to determine a recommended daily allowance for vitamin D. Instead, adequate intake (AI) has been
determined throughout the lifespan. The AI, expressed in international units (IU), for each age group is as follows:

Birth to 50 years: 200 IU per day
Age 51 to 70: 400 IU per day
Age 71 and older: 600 IU per day

The upper limit for adults for vitamin D through diet is 2,000 IU per day. Exceeding the upper limit may cause nausea, vomiting, poor appetite, constipation, and muscle weakness. Over a long term, exceeding the upper limit 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 between 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 individuals taking high doses of vitamin D. Those taking 1,000 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 a high 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, so more research is needed. At this time spokespeople for the American Cancer Society believe that it is safe to take up to 1,000 IU of vitamin D per day to decrease the risk of developing certain forms of cancer.

Conclusion

Vitamin D is a fat-soluble vitamin 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 supplement is recommended. Calcium supplements often contain vitamin D and together help promote good bone health. Until more-conclusive evidence is found, the Institute of Medicine recommends between 200 and 600 IU of vitamin D per day. Individuals with a family history of colon, breast, or ovarian cancer may want to discuss taking higher amounts of vitamin D with their physician.