Pay attention on what I'm saying: "Vitamin" is an extremely good manga. Yes, it's definetively a story about bullying, but it touches many other significative issues to the youth.
Which makes the manga so outstanding, despite it's good portion of melodrama, is the realism of the situations. In many other shoujo series Kouta's abusive attitude towards his girlfriend Sawako would be fetichized, but what the author shows us is what the character actually is: an unrespectful jerk. And "thanks" his reckless behavior Sawako becomes a bullying victim and slut-shamed as hell( and slut-shaming is a problem in Japan, just see what happened to the AKB0048 member who admitted to have had encounters with a man). It's also worth noting the bold criticism the author makes to the Japanese school system. Sawako's teachers and principals are clearly only worried about how well the students will perform on tests and don't seem to realise(or simply ignore) the pain the girl is going through. Her salvation will be reconnecting with her childhood dreams that all the pressure and padronization of school killed.
The story may be heavy and feature some sexual and violent scenes, but I think teenagers really should read this manga. It's not an easy reading, but is relatable to young people and it's going to make you think after finishing it.