The Effect of a Meal on Vitamin D Absorption

Vitamin D supplements are increasingly recommended to curb widespread deficiency. Decreasing the variability in 25OHD responses to supplemental vitamin D would make the supplementation process more predictable, and thereby reduce the number of 25OHD measurements and dose adjustments that are needed to achieve the targeted 25OHD level. This study seeks to identify potential sources of variability in the 25OHD3 response to supplemental vitamin D3 that are plausible based on rat studies, but have not been explored in humans. The investigators hypothesize that the serum 25OHD3 response to supplemental vitamin D3 in healthy adults will be enhanced in the presence of a meal and the enhancement will be greater when the meal is low as opposed to high in fat content. The enhancement will result from increased vitamin D absorption. The investigators will test this hypothesis by pursuing the following aims in a 3-mo trial in which up to 70 healthy men and women will be randomized to one of the following meal conditions under which they will take a monthly oral dose of 50,000 IU of vitamin D3: no meal (fasting), a low fat meal, or an iso-caloric high fat meal. Serum 25OHD3 will be measured at baseline and after 1 and 3 mo. A serum vitamin D3 absorption test will be performed in each subject after the first dose of vitamin D. The Primary Aim is to identify the meal condition (fasting, low-fat, or high-fat meal) under which the 25OHD3 response to supplemental vitamin D3 is greatest and most consistent. The Secondary Aim is to determine whether vitamin D3 absorption is affected by the meal condition and to determine whether the absorption of vitamin D3 predicts the longer-term 25OHD3 response to supplementation.