Is it true that reading too many comics does harm to the reading and writing skill?

I remember reading about a survey about the effect of comics on people conducted in Japan a long time ago in a teen’s magazine (sorry for not being able to find the source anymore). The result of the survey showed that the more comics someone read, the less able they were to read and write a moderately complex sentence properly. The conclusion was that comics could hamper greatly to the reading and writing skill since they contained too short, too simple and too grammatically incorrect sentences.

And recently my friend told me about her family: she had a sister who, according to her, “proceeds a natural talent for literature”. As a result her mother designed a special “training program” for her. The sister was forbidden to read any comics and only classic books were allowed instead. My friend totally agreed with her mother, saying that comics would do harm to her writing skill as well as her imagination. I argued that when I was at the sister’s age, half of what I read were comics, still my writing skill was unaffected and my imagination improved with time. She just said plainly: “It’s because you are a born writer, that’s all”.

I never consider myself having any talent, and I feel odd. My life experience doesn’t match with the result of the above-mentioned study and anyone’s opinion about comics. Is it true that comics does harm to the reading and writing skill? What do you think?