Direct Exposure to Sunlight Accelerates Vitamin D Biodegradation in Milk
Ronald C Hamdy , Reza M Mohseni , Edith Seier , W Andrew Clark and Jennifer Culp
Journal Title:Journal of Clinical Nutrition and Food Science
Background: Vitamin D is essential for the gastrointestinal absorption of calcium and mechanical integrity of the musculoskeletal system. It can be ingested and is also produced in the skin by the action of ultraviolet (UV) sunlight on 7-dehydro-cholesterol, converting it to cholecalciferol. Given the risks of exposure to sunlight and convenient availability of sunblock lotions, many people tend to rely on the oral intake of vitamin D. In the United States milk is routinely fortified with vitamin D and is one of the primary dietary sources of the vitamin. Hypovitaminosis D is nevertheless quite prevalent and has been associated with a number of pathologies. Objective: The purpose of our study is to determine whether the rate of cholecalciferol biodegradation in fortified milk is accelerated by exposure to direct sunlight. Methods: This study was conducted on a sunny day when the temperature was 72°F. Commercially available skim milk was used. Three clear glass containers of milk were placed under direct sunlight, 3 in an adjacent shaded area, and 3 in a refrigerator. Samples from each container were obtained at 0, 5, 10, 30, 60, and 90 minutes. The modified AOAC Official Method 992.26 and high performance liquid chromatography (HPLC) were utilized to extract and analyze cholecalciferol, and the Vitamin D content (mg/L) was calculated using the BeerLambert law. Results: Our data show that the vitamin D content of fortified milk decreases significantly (to about 80% of its original value) over a period of 60 minutes when exposed to direct sunlight. The vitamin D content of fortified milk kept unrefrigerated in shade also decreases over a period of 60 minutes (by about 10%), but the vitamin D content of samples kept refrigerated remains largely unchanged. Conclusions: Vitamin D degradation in milk exposed to sunshine occurs steadily over a period of 10 minutes to 60 minutes, leveling off between 60 and 90 minutes. Vitamin D content of fortified milk stored in a refrigerator remains consistent throughout the time period tested.