Welcome to HCM.Masturbation
has no ill effect on health. Being thin does not cause any problem. It does affect your personality and your social interaction, if you are completely obsessed with masturbation. Sex should not dominate you, it has to be well under your control, otherwise you will find it difficult to cope with your daily life activities.
As the saying goes : "Too much of every thing is harmful". So observing moderation and caution is always beneficial.
Take Care and best of luck.