Editorial See corresponding articles on pages 1350 and 1357.

Vitamin D status continues to decline in the United States be-cause of lifestyle factors such as decreased outdoor activity (1). Exposure to sunlight is one of the major determinants of an in-dividual’s vitamin D status. Because the amount of sunlight nec-essary for optimal vitamin D status varies by individual factors (skin tone, adiposity, age), latitude, season, and time of day, and because of concerns over skin cancer risk, it is difficult to recom-mend increased exposure to sunlight as a public health strategy to improve vitamin D status in the US population. Therefore, there has been increased interest in improving vitamin D status by either recommending vitamin D supplement use or fortifying foods with vitamin D. Some foods such as meat, fish, and eggs contain vitamin D naturally as the hydroxylated vitamin D me-tabolite 25-hydroxyvitamin D [25(OH)D3]. However, it is un-known whether 25(OH)D3 found in foods or supplements ha