Suggestion that Vitamin D May Protect against Breast Cancer
2006; Wolters Kluwer; Volume: 28; Issue: 12 Linguagem: Inglês
10.1097/01.cot.0000295115.70437.fc
ISSN1548-4688
Autores Tópico(s)Vitamin D Research Studies
ResumoWASHINGTON, DC—Vitamin D may help protect against breast cancer, researchers reported here at the American Association for Cancer Research Annual Meeting. One new study suggests that taking at least 1,000 IU of vitamin D daily on top of what one gets in the diet can slash the risk of breast cancer by 10% to 50%, said Cedric Garland, DrPH, Professor of Family and Preventive Medicine at the University of Caliornia, San Diego. Another study suggests that consuming adequate amounts of vitamin D during adolescence and young adulthood may be particularly important for lowering breast cancer risk. Dr. Garland estimated that at least half of American women suffer from vitamin D deficiencies that place them at increased risk of breast cancer. A Scientific Rationale Dr. Garland noted that he and E.D. Gorham, PhD, first proposed in 1990 that vitamin D may protect against breast cancer based on the geographical distribution of breast cancer mortality rates in the United States (Prev Med 1990;19:614–622). “The study revealed higher rates in the Northeast, where long dark winters deprive people of vitamin D, and lower rates in the Southwest,” Dr. Garland said. “The findings were then replicated in other studies—the closer you get to the equator, the lower your risk of breast-cancer death.” Risk Cut in Half In the new research, Dr. Garland and colleagues performed a meta-analysis of the two studies they found in the literature that compared breast cancer rates and serum vitamin D levels. The 1,760 women in the pooled analysis were divided into quintiles depending on their serum levels of 25-hydroxyvitamin D: 0 to ng/ml; 12 to 25 ng/ml; 26 to 31 ng/ml; 32 to 42 ng/ml; and over 42 ng/ml. Dr. Garland noted that 25-hydroxyvitamin D, more commonly referred to as vitamin D-3 or cholecalciferol, is the active form synthesized by the body when in the sun. Results showed that women in the highest quintile of vitamin D-3 intake were 50% less likely to develop breast cancer than those with the lowest levels. But very few women achieved that, Dr. Garland said. But even women in the second lowest quintile—that is, with serum levels of 12 to 25 ng/ml—were 10% less likely to develop breast cancer than those with the lowest levels, he said. A multiple regression analysis showed that a vitamin D-3 level of over 52 ng/ml was associated with a 50% lower risk of breast cancer, compared with levels of less than 12 ng/ml. Sun Exposure a Factor In a separate population-based case-control study, Julia A. Knight, PhD, a scientist in the Division of Epidemiology and Biostatistics at Mount Sinai Hospital in Toronto, and colleagues conducted telephone interviews with 576 women who had been diagnosed with breast cancer and 1,135 women without cancer. The women, aged 20 to 59 years, were asked about sun exposure and diet throughout their lives. Women who worked in more than six outdoor jobs between the ages of 10 and 19 years were 45% less likely to develop breast cancer than those who worked in fewer than four outdoor jobs. Women who worked in more than six outdoor jobs between the ages of 10 and 19 years were 45% less likely to develop breast cancer than those who worked in fewer than four outdoor jobs. And when the women were divided into quartiles depending on how many different outdoor activities they engaged in between the ages of 10 and 19 years, those in the highest quartile were 32% less likely to develop breast cancer than those in the lowest quartile.Figure: William G. Nelson, MD, PhD: “There are hints that higher amounts of vitamin D may be even more protective, but for now, 1,000 IU is likely to be safe and have a breast-cancer protective effecthellip;.Most patients do not even know their vitamin D serum levels. I would think it would be rational for clinicians to begin measuring such levels as part of a routine checkup.”“Outdoor activities” included those that do not involve physical activity, thus making it an accurate reflection of sun exposure, Dr. Knight said. The study also showed that women who consumed vitamin D-rich cod liver oil for 10 years or more were 36% less likely to develop breast cancer, compared with those who did not consume cod liver. Additionally, women aged 20 to 29 years who drank more than nine glasses of milk a week were one fourth less likely to develop breast cancer compared with those who consumed fewer than five glasses. Young Exposure Crucial In the study, each vitamin-D related variable was adjusted for age, ethnicity, education, having a first-degree relative with breast cancer, ever breastfeeding for at least one month, age at menarche, and age at first birth. “A major finding was that much of the protective factors were most important when women were aged 10 to 29 years,” Dr. Knight said. “This preliminary analysis provides support for the hypothesis that vitamin D may reduce the risk of breast cancer and earlier exposures may be more important than recent exposure,” she said. “Current thinking is that exposures during adolescence or before a full-term pregnancy may have a greater effect, as that is when breast tissue is going through the most rapid development,” Dr. Knight said. Diet Alone Doesn't Do the Job Current recommendations call for people between the ages of 1 and 50 to consume 200 IU of vitamin D daily, with 400 IU recommended for those between the ages of 51 and 70. After age 70, the recommendation is for 600 IU of vitamin D each day. But given widespread vitamin D deficiency, those recommendations are too low, Dr. Garland said. “To maintain a cancer-protective level [of over 52 ng/ml], an average 70 kg woman would have to take in at least 2,700 IU of vitamin D daily, which is higher than the ‘No Adverse Effect Level’ of 2,400 IU/day established by the National Academy of Sciences.” That said, there have been concerns that too much vitamin D can be toxic, particularly to the kidney, he acknowledged. “While it's becoming clear that you can monitor for problems, a recommendation of 1,000 IU per day is probably safest for now,” he said. William G. Nelson, MD, PhD, Professor of Oncology, Urology, Pharmacology, Medicine, Pathology, and Radiation Oncology at Johns Hopkins University, agreed. “There are hints that higher amounts may be even more protective, but for now 1,000 IU is likely to be safe and have a cancer-protective effect,” said Dr. Nelson, who monitored a press conference to discuss the findings. Dr. Garland stressed that it is nearly impossible to get enough vitamin D in the diet alone. An eight-ounce glass of milk, for example, contains only 100 IU of vitamin D, and a serving of cereal has 20 IU. “You need a supplement,” he said. Not All Supplements Equal Not all vitamin D supplements are created equal, Dr. Garland stressed. Most use the older form—D-2, or ergocalciferol—which is far less potent than D-3, he said. “There are 900 or so studies in animals or cells indicating that vitamin D-3 is a far more powerful anti-carcinogenic.” Multivitamins typically contain only small amounts of D-2 and include vitamin A, which offsets many of vitamin D's benefits, he added. “It may be hard to find and expensive to find it, but you want to tell your patients to take vitamin D-3,” Dr. Garland said. Dr. Nelson noted that most patients do not even know their vitamin D serum levels. “I would think it would be rational for clinicians to begin measuring such levels as part of a routine checkup,” he said.
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