As people's life and work gradually enter high-rise buildings, people have less exposure to daylight. It is found that sunlight is a necessary condition for the synthesis of vitamin D, and vitamin D is a key factor to promote calcium absorption. 
Osteoporosis patients can be relieved or cured by getting more sun
 some people have come to the conclusion that modern people are more likely to suffer from diseases such as osteoporosis caused by calcium deficiency.