Prematurely aging kids (Hutchinson-Gilford Progeria Syndrome) might be helped by Vitamin D– March 2018

Extremely rare: Fewer than 1,000 cases per year in the US
"HGPS is caused by the random mutation of a single gene that causes children to age rapidly. Children with the condition develop many of the typical changes and illness associated with aging, including hair loss, aging skin, joint abnormalities, and bone loss. The disease causes atherosclerosis—fatty deposits that clog arteries—and patients with the illness die from cardiovascular complications such as stroke or myocardial infarction in their teens."