There are more than 10,000 known rare diseases.
Approximately 80% of rare diseases are estimated to have a genetic origin.
Of those, 70% start in childhood. (56% of rare diseases start in childhood)
- "In the United States, about half of the people with a rare disease are children. Many of these diseases are chronic and worsen over time."
The US defines incidence of a "rare disease" as being 1 in every 1,500 people
The founder of VitaminDWiki has seen many "rare" diseases fought by Vitamin D, but had not posted them since so few people would be interested in each disease
Google Scholar Sept 2023 11,000 hits for "rare disease" "vitamin d"