Have been taking vitamin c supplements (500mg) for a week now and started getting knee pain. can vit c cause knee pain?

No: It is a coincidence. "(500mg) for a week " is insignificant. However, researchers say dietary Intake should not be above the RDA recommendation. The recent study showed long-term use of vitamin C supplements worsened the severity of osteoarthritis. Hope it helps.

No; however...: I've had thousands of patients take Vit C & none have reported knee pain; it's not a known side effect. While vitamin C itself can not do it, the form you are taking might have fillers & binders you are allergic to; also most C comes from corn & if you're allergic to corn it might cause a reaction. Try stopping 2 weeks, see if pain goes away, then restart. If pain recurs try C from non-corn source.