Poor mental health can be a risk factor for many conditions including chronic physical conditions which are leading a person to fail in social aspects of life. People who have chronic physical conditions are at risk of developing bad or poor mental health that will affect their social aspects because they can have lower self-esteem and feel bad about themselves so they will think that others will think that too.
The thing wrong with this study is that it could very possibly be wrong, seeing as how it was funded by a candy company. They could have very well influenced the outcome of the study.