Women were aged 55+ with an average age of 63, data collected was from 2002 to 2017, participants were free of cancer at the start of study, and were followed for 4 years, with participant vitamin D levels in blood being measured during study visits. 77 cases of breast cancer were diagnosed over the course of the studies with an age adjusted incidence rate of 512 case per 100,000 person years.
Minimum healthy level of 25 (OH)D in blood plasma was identified by the researchers to be 60 nanograms per milliliter, which is higher than the recommended 20 mg/ml. Participants with blood levels of 25(OH)D that were above 60 ng/ml were found to be at one fifth the risk of breast cancer than those at 20 ng/ml. Multivariate regression was used to quantify the association, results were adjusted for BMI, age, intake of calcium supplements, and cigarette smoking.
Researchers conducted this study building on previous epidemiological research linking vitamin D deficiency to increased risk of breast cancer. Though it has been argued that they do not necessarily prove cause and effect, epidemiological studies analyze distribution and determinants of health and disease.
This study was limited to postmenopausal breast cancer, additional research is required to determine whether high 25(OH)D levels may prevent premenopausal breast cancer; participants were mainly white making further research required for other ethnic groups. Even with limitations findings suggest strong association between serum vitamin D and decreased risk of breast cancer.
Dietary supplements of 4,000 to 6,000 international units per day are required to reach 25(OH)D levels of 60 ng/ml, which could be less with addition of moderate daily sun exposure. Blood test should be conducted to determine success of oral supplementation.
The National Academy of Medicine recommends an average daily amount of vitamin D3 of 400 IU for infants 1 year old and under, 600 IU for ages 1 to 70, and 800 IU for ages 70+. In a statement published in Annals of Epidemiology researchers recommend a healthy target level of serum 25(OH)D of 40 to 60 ng/ml based on expert consensus panel. Oral doses are not always specified as individuals require different intake to achieve targets. Intake of vitamin D3 should not exceed 10,000 units per day unless under medical supervision and monitoring as levels above 125 ng/ml are linked to adverse side effects including constipation, weight loss, nausea, kidney damage, and heart rhythm problems.
