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. 
People with osteoporosis spend the same amount of time exposed to sunlight as others.
 some people have concluded that modern people are more likely to suffer from osteoporosis and other diseases caused by calcium deficiency.