As people's life and work gradually in high-rise buildings, people have fewer opportunities to be exposed to sunlight. Studies have found that sunlight is a necessary condition for the synthesis of vitamin D, and vitamin D is a key factor in promoting calcium absorption. 
Oral vitamin D tablets are synthetic formulas added with absorption enhancers.
 some people have concluded that modern people are more likely to suffer from osteoporosis and other diseases caused by calcium deficiency.