I know of no problems from excess ingestion of Vitamin C. But B6 is
another matter:
from "Safe Upper Levels for Vitamins and Minerals"
May 2003
Expert Group on Vitamins and Minerals
UK
Long-term use of pyridoxine (generally in excess of 200 mg/day) has
been reported to result in paraesthesiae, somnolence and low serum
folic acid levels. Large doses of pyridoxine (usually quoted as over
2000 mg/day) can cause nerve damage. Symptoms include tingling in the
hands and feet (paraesthesiae), a stumbling gait, perioral numbness,
a characteristic stocking-glove sensory loss and lack of muscle
coordination. Duration of pyridoxine use is important as well as
dosage, with lower doses of pyridoxine (500 mg/day or less) consumed
for many months or years also being associated with neuropathy. In
most, but not all reported cases the damage has been generally
reversible. Night restlessness, vivid dreams, sun sensitivity and an
acne-like rash may also occur with high doses (150 mg/day or more) of
pyridoxine.