Am i harming my body by taking food based multivitamin and fish oil? i heard on the news that overdose of certain vitamins can cause cancer.

Vitamin E: Ingestion of excessive amounts of vitamin e has been associated with increased incidence of prostate cancer.

Probably not, but...: Probably not helping much either, if diverse diet, no significant liver, kidney, bowel disease. If compelled yo take a supplement, stay away from megadoses to minimize risk of imbalance or overdosing. High doses can cause gut complaints, like nausea, gas, bloat. Supplements isn't same as diet intake, and in studies results aren't as good (generally); could be if eat better, take bettercare ofself.