“Over time, the prevalence of vitamin D deficiency appears to be increasing,” Dr. Saintonge said. “Over the past few decades, there has been a decrease in [vitamin D] fortified milk intake among children and adolescents. Generally, most adults don't drink milk regularly,” she said in an interview. In addition, many factors interfere with cutaneous vitamin D production. The U.S. public needs a broad vitamin D fortification strategy, along with possibly routine serum monitoring of vitamin D levels, Dr. Saintonge said.