Closing a credit card bad credit?

I maxed out a problem with the credit card, and recently off a card with a line of credit is very important to help pay for my parents. I want to close the account, so I do not use it again, but I heard that it has a negative effect on my credit rating. Is this true and if so, how much of a negative effect? I try, the risk of me caving and accumulating more debt against the final effect on my credit score for mortgages, loans and support, student loans, etc. to consider in the future.