Vitamin D Reduces Cancer Risk - Sun Not Enough

Most Americans and others are not taking enough vitamin D, a fact that may put them at significant risk for developing cancer, according to a landmark study conducted by Creighton University School of Medicine.

The four-year, randomized study followed 1,179 healthy, postmenopausal women from rural eastern Nebraska.* Participants taking calcium, as well as a quantity of vitamin D3 nearly three times the U.S. government’s Recommended Daily Amount (RDA) for middle-age adults, showed a dramatic 60 percent or greater reduction in cancer risk than women who did not get the vitamin.

The results of the study, conducted between 2000 and 2005, were reported in the June 8 online edition of the American Journal of Clinical Nutrition.

“The findings are very exciting. They confirm what a number of vitamin D proponents have suspected for some time but that, until now, have not been substantiated through clinical trial,” said principal investigator Joan Lappe, Ph.D., R.N., Creighton professor of medicine and holder of the Criss/Beirne Endowed Chair in the School of Nursing. “Vitamin D is a critical tool in fighting cancer as well as many other diseases.”

Research participants were all 55 years and older and free of known cancers for at least 10 years prior to entering the Creighton study. Subjects were randomly assigned to take daily dosages of 1,400-1,500 mg supplemental calcium, 1,400-1,500 mg supplemental calcium plus 1,100 IU of vitamin D3, or placebos. National Institutes of Health funded the study.

Over the course of four years, women in the calcium/vitamin D3 group experienced a 60 percent decrease in their cancer risk than the group taking placebos.

On the premise that some women entered the study with undiagnosed cancers, researchers then eliminated the first-year results and looked at the last three years of the study. When they did that, the results became even more dramatic with the calcium/vitamin D3 group showing a startling 77 percent cancer-risk reduction.

In the three-year analysis, there was no statistically significant difference in cancer incidence between participants taking placebos and those taking just calcium supplements.

Through the course of the study, 50 participants developed nonskin cancers, including breast, colon, lung and other cancers.

Lappe said further studies are needed to determine whether the Creighton research results apply to other populations, including men, women of all ages, and different ethnic groups. While the study was open to all ethnic groups, all participants were Caucasian, she noted.

There is a growing body of evidence that a higher intake of vitamin D may be helpful in the prevention and treatment of cancer, high blood pressure, fibromyalgia, diabetes mellitus, multiple sclerosis, and rheumatoid arthritis and other diseases.

Humans make their own vitamin D3 when they are exposed to sunlight. In fact, only 10-15 minutes a day in a bright summer sun creates large amounts of the vitamin, Lappe said. However, people need to exercise caution since the sun’s ultraviolet B rays also can cause skin cancer; sunscreen blocks most vitamin D production.

In addition, the latitude at which you live and your ancestry also influence your body’s ability to convert sunlight into vitamin D. People with dark skin have more difficulty making the vitamin. Persons living at latitudes north of the 37th parallel – Omaha is near the 41st parallel – cannot get their vitamin D naturally during the winter months because of the sun’s angle.

Experts generally agree that the RDA** for vitamin D needs to be increased substantially, however there is debate about the amount. Supplements are available in two forms – vitamin D2 and vitamin D3. Creighton researchers recommend vitamin D3 , because it is more active and thus more effective in humans.

It’s not yet clear why overweight elderly adults have low levels of vitamin D in their blood. However, researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (USDA HNRCA) have found that lack of sun exposure may not account for low levels of vitamin D in elders who are overweight.

“People aged 65 and over with high percent body fat have lower levels of 25-hydroxyvitamin D, the storage form of vitamin D, compared to those who have lower percent body fat,” says corresponding author Susan Harris, DSc, epidemiologist in the Bone Metabolism Laboratory at the USDA HNRCA.

Harris and co-author Bess Dawson-Hughes, MD, director of the Bone Metabolism Laboratory at the USDA HNRCA, interviewed 381 Caucasian men and women aged 65 and over about their sun exposure over a previous three-month period.
Individuals reported how much time they spent outdoors, how much skin was exposed while outdoors, and whether or not they wore sunscreen. Seasonality, or when the individual entered the study, was also taken into account, because in Boston, where the study was conducted, sun rays are weak in winter compared with summer months. The researchers measured participants’ percent body fat using dual-energy x-ray absorptiometry (DXA), a precise method for determining body composition. Individuals were grouped into quartiles of percent body fat: less than 28 percent, 28 percent to 33 percent, 34 percent to 40 percent, and greater than 40 percent. Blood levels of 25-hydroxyvitamin D were measured and participants were asked to fill out a dietary questionnaire to measure the amount of vitamin D they obtained from food.

Harris and Dawson-Hughes found that when adjusted for sex, age, seasonality and dietary vitamin D intake, 25-hydroxyvitamin D significantly decreased as body fat increased, (P<0.024). When the researchers further adjusted for sunlight exposure variables, 25-hydroxyvitamin D values still significantly decreased as body fat increased. “Sunlight exposure could not account for low vitamin D stores in older people with high percent body fat,” explains Harris.

Vitamin D is called the “sunshine vitamin” because it is produced by the body when the skin is exposed to ultraviolet (UV) rays from the sun. Vitamin D can also be obtained from foods such as fish and fortified milk and from supplements. When this fat-soluble vitamin enters the body it is converted in the liver to 25-hydroxyvitamin D. This is one of several important forms of vitamin D, and is the form that researchers and clinicians use as an indicator of vitamin D status in individuals. “Vitamin D is especially critical in maintaining bone health, and there is evidence that many older Americans have low blood levels of vitamin D, which can put them at risk for bone fractures and osteoporosis,” says Dawson-Hughes, who is also a professor at Tufts University School of Medicine.

“These results cannot be carried over to other populations, such as young people, or elderly living in different climates. However, if low vitamin D stores are not attributed to low sunlight exposure in this population, it suggests that we should explore other possibilities,” says Harris. “The most likely explanation seems to be that vitamin D is sequestered in fat tissue, reducing its entry into the blood.”

This study was supported by the Agricultural Research Service of the U.S. Department of Agriculture and by a grant from the National Institutes of Health.