Hello,
Well, smartphone use may not directly cause depression; but yes, excessive use or problematic use of smartphone can be an important risk factor for any stress related disorders like depression and anxiety. It is observed that there is been a very strong association of smartphone use with feeling of loneliness, poor physical health, reduced social interaction, disturbed sleep patterns, etc. These factors are very strong indicators of depression. So in a way ,yes, problematic or excessive use does contribute to the risk for depression.
Remember, any habit be it watching TV, drinking or in your case phone use, if it becomes priority over other important responsibilities, if you are getting distressed by its use or when you are not using it, then it means that the habit has become problematic. In worse case there can even develop addiction to it.
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