Dear lit_hua_nia,
Yes, personally I think so!!!
Those who always sleep at midnight, like 2:00 or 3:00 in the early morning would have the Yin deficiency. As the consequence, they would have a bad health condition in their senior years, or even their life span would be decreased.
Of course there could be more or less variation from person to person, but as a general rule, it cannot be denied to have this consequence, earlier or later in future.
This is our idea in traditional Chinese medicine, also in Daoist (Taoist) concept.
Tutor |