Higher levels of vitamin D are associated with decreasing risk of breast cancer, says a study led by researchers at University of California San Diego School of Medicine, U.S. The scientists pooled data from two randomised clinical trials with 3,325 combined participants and a prospective study involving 1,713 participants to examine the association between risk of female breast cancer and a broad range of serum 25-hydroxyvitamin D —25(OH)D — concentrations, which was chosen as the marker because it is the main form of vitamin D in the blood.
Researchers identified the minimum healthy level of 25(OH)D in blood plasma to be 60 nanograms per millilitre, substantially higher than the previous medically recommended standard of 20 ng/ml.
“We found that participants with blood levels of 25(OH)D that were above 60 ng/ml had one-fifth the risk of breast cancer compared to those with less than 20 ng/ml,” said principal investigator and co-author Cedric F. Garland, DrPH, adjunct professor in the UC San Diego Department of Family Medicine and Public Health, in a press statement. The risk of cancer appeared to decline with greater levels of serum vitamin D.
Dr. Garland, who has previously studied connections between serum vitamin D levels and several types of cancer, said the study builds upon previous epidemiological research linking vitamin D deficiency to a higher risk of breast cancer. Epidemiological studies analyse the distribution and determinants of health and disease, but it has been argued that they do not necessarily prove cause-and-effect.
“This study was limited to postmenopausal breast cancer. Further research is needed on whether high 25(OH)D levels might prevent premenopausal breast cancer,” he said. As the population was also mainly white women, further research is needed on other ethnic groups.
Long-time advocate
Dr. Garland and others have advocated the health benefits of vitamin D for many years. In 1980, he and his late brother, Frank C. Garland, also an epidemiologist, published an influential paper that posited vitamin D (produced by the body through exposure to sunshine) and calcium (which vitamin D helps the body absorb) together reduced the risk of colon cancer. The Garlands and colleagues subsequently found favourable associations of markers of vitamin D with breast, lung and bladder cancers, multiple myeloma and adult leukaemia.
To reach 25(OH)D levels of 60 ng/ml would generally require dietary supplements of 4,000 to 6,000 international units (IU) per day, less with the addition of moderate daily sun exposure wearing very minimal clothing (approximately 10-15 minutes per day outdoors at noon), Dr. Garland said. The success of oral supplementation should be determined using a blood test, preferably during winter months, he added.
According to the National Academy of Medicine, U.S., the current recommended average daily amount of vitamin D3 is 400 IU for children up to one year; 600 IU for ages one to 70 years (including pregnant or breastfeeding women); and 800 IU for persons over the age of 70.
Blood serum levels exceeding 125 ng/ml have been linked to adverse side-effects, such as nausea, constipation, weight loss, heart rhythm problems and kidney damage.
jacob.koshy@thehindu.co.in
