  As social interactions are increasingly taking place in the digital
environment, online friendship and its effects on various life outcomes from
health to happiness attract growing research attention. In most studies, online
ties are treated as representing a single type of relationship. However, our
online friendship networks are not homogeneous and could include close
connections, e.g. a partner, as well as people we have never met in person. In
this paper, we investigate the potentially differential effects of online
friendship ties on mental health. Using data from a Russian panel study (N =
4,400), we find that - consistently with previous research - the number of
online friends correlates with depression symptoms. However, this is true only
for networks that do not exceed Dunbar's number in size (N <= 150) and only for
core but not peripheral nodes of a friendship network. The findings suggest
that online friendship could encode different types of social relationships
that should be treated separately while investigating the association between
online social integration and life outcomes, in particular well-being or mental
health.
